x86: kmsan: don't instrument stack walking functions

Upon function exit, KMSAN marks local variables as uninitialized. Further
function calls may result in the compiler creating the stack frame where
these local variables resided. This results in frame pointers being
marked as uninitialized data, which is normally correct, because they are
not stack-allocated.

However stack unwinding functions are supposed to read and dereference the
frame pointers, in which case KMSAN might be reporting uses of
uninitialized values.

To work around that, we mark update_stack_state(), unwind_next_frame() and
show_trace_log_lvl() with __no_kmsan_checks, preventing all KMSAN reports
inside those functions and making them return initialized values.

Link: https://lkml.kernel.org/r/20220915150417.722975-40-glider@google.com
Signed-off-by: Alexander Potapenko <glider@google.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Alexei Starovoitov <ast@kernel.org>
Cc: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Andrey Konovalov <andreyknvl@google.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Eric Biggers <ebiggers@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Ilya Leoshkevich <iii@linux.ibm.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Pekka Enberg <penberg@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

x86/unwind: Recover kretprobe trampoline entry

Since the kretprobe replaces the function return address with
the kretprobe_trampoline on the stack, x86 unwinders can not
continue the stack unwinding at that point, or record
kretprobe_trampoline instead of correct return address.

To fix this issue, find the correct return address from task's
kretprobe_instances as like as function-graph tracer does.

With this fix, the unwinder can correctly unwind the stack
from kretprobe event on x86, as below.

<...>-135 [003] ...1 6.722338: r_full_proxy_read_0: (vfs_read+0xab/0x1a0 <- full_proxy_read)
<...>-135 [003] ...1 6.722377: <stack trace>
=> kretprobe_trace_func+0x209/0x2f0
=> kretprobe_dispatcher+0x4a/0x70
=> __kretprobe_trampoline_handler+0xca/0x150
=> trampoline_handler+0x44/0x70
=> kretprobe_trampoline+0x2a/0x50
=> vfs_read+0xab/0x1a0
=> ksys_read+0x5f/0xe0
=> do_syscall_64+0x33/0x40
=> entry_SYSCALL_64_after_hwframe+0x44/0xae

Link: https://lkml.kernel.org/r/163163055130.489837.5161749078833497255.stgit@devnote2

Reported-by: Daniel Xu <dxu@dxuuu.xyz>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Suggested-by: Josh Poimboeuf <jpoimboe@redhat.com>
Tested-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

exec: Implement kernel_execve

To allow the kernel not to play games with set_fs to call exec
implement kernel_execve. The function kernel_execve takes pointers
into kernel memory and copies the values pointed to onto the new
userspace stack.

The calls with arguments from kernel space of do_execve are replaced
with calls to kernel_execve.

The calls do_execve and do_execveat are made static as there are now
no callers outside of exec.

The comments that mention do_execve are updated to refer to
kernel_execve or execve depending on the circumstances. In addition
to correcting the comments, this makes it easy to grep for do_execve
and verify it is not used.

Inspired-by: https://lkml.kernel.org/r/20200627072704.2447163-1-hch@lst.de
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/87wo365ikj.fsf@x220.int.ebiederm.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

arch: rename copy_thread_tls() back to copy_thread()

Now that HAVE_COPY_THREAD_TLS has been removed, rename copy_thread_tls()
back simply copy_thread(). It's a simpler name, and doesn't imply that only
tls is copied here. This finishes an outstanding chunk of internal process
creation work since we've added clone3().

Cc: linux-arch@vger.kernel.org
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>A
Acked-by: Stafford Horne <shorne@gmail.com>
Acked-by: Greentime Hu <green.hu@gmail.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>A
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>

x86/entry: Unbreak __irqentry_text_start/end magic

The entry rework moved interrupt entry code from the irqentry to the
noinstr section which made the irqentry section empty.

This breaks boundary checks which rely on the __irqentry_text_start/end
markers to find out whether a function in a stack trace is
interrupt/exception entry code. This affects the function graph tracer and
filter_irq_stacks().

As the IDT entry points are all sequentialy emitted this is rather simple
to unbreak by injecting __irqentry_text_start/end as global labels.

To make this work correctly:

- Remove the IRQENTRY_TEXT section from the x86 linker script
- Define __irqentry so it breaks the build if it's used
- Adjust the entry mirroring in PTI
- Remove the redundant kprobes and unwinder bound checks

Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

x86/unwind: Prevent false warnings for non-current tasks

There's some daring kernel code out there which dumps the stack of
another task without first making sure the task is inactive. If the
task happens to be running while the unwinder is reading the stack,
unusual unwinder warnings can result.

There's no race-free way for the unwinder to know whether such a warning
is legitimate, so just disable unwinder warnings for all non-current
tasks.

Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Dave Jones <dsj@fb.com>
Cc: Jann Horn <jannh@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: https://lore.kernel.org/r/ec424a2aea1d461eb30cab48a28c6433de2ab784.1587808742.git.jpoimboe@redhat.com

x86/stackframe/32: Provide consistent pt_regs

Currently pt_regs on x86_32 has an oddity in that kernel regs
(!user_mode(regs)) are short two entries (esp/ss). This means that any
code trying to use them (typically: regs->sp) needs to jump through
some unfortunate hoops.

Change the entry code to fix this up and create a full pt_regs frame.

This then simplifies various trampolines in ftrace and kprobes, the
stack unwinder, ptrace, kdump and kgdb.

Much thanks to Josh for help with the cleanups!

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

treewide: Add SPDX license identifier for missed files

Add SPDX license identifiers to all files which:

- Have no license information of any form

- Have EXPORT_.*_SYMBOL_GPL inside which was used in the
initial scan/conversion to ignore the file

These files fall under the project license, GPL v2 only. The resulting SPDX
license identifier is:

GPL-2.0-only

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

x86/unwind: Handle NULL pointer calls better in frame unwinder

When the frame unwinder is invoked for an oops caused by a call to NULL, it
currently skips the parent function because BP still points to the parent's
stack frame; the (nonexistent) current function only has the first half of
a stack frame, and BP doesn't point to it yet.

Add a special case for IP==0 that calculates a fake BP from SP, then uses
the real BP for the next frame.

Note that this handles first_frame specially: Return information about the
parent function as long as the saved IP is >=first_frame, even if the fake
BP points below it.

With an artificially-added NULL call in prctl_set_seccomp(), before this
patch, the trace is:

Call Trace:
? prctl_set_seccomp+0x3a/0x50
__x64_sys_prctl+0x457/0x6f0
? __ia32_sys_prctl+0x750/0x750
do_syscall_64+0x72/0x160
entry_SYSCALL_64_after_hwframe+0x44/0xa9

After this patch, the trace is:

Call Trace:
prctl_set_seccomp+0x3a/0x50
__x64_sys_prctl+0x457/0x6f0
? __ia32_sys_prctl+0x750/0x750
do_syscall_64+0x72/0x160
entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Jann Horn <jannh@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: syzbot <syzbot+ca95b2b7aef9e7cbd6ab@syzkaller.appspotmail.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Michal Marek <michal.lkml@markovi.net>
Cc: linux-kbuild@vger.kernel.org
Link: https://lkml.kernel.org/r/20190301031201.7416-1-jannh@google.com

x86/unwind: Disable unwinder warnings on 32-bit

x86-32 doesn't have stack validation, so in most cases it doesn't make
sense to warn about bad frame pointers.

Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a69658760800bf281e6353248c23e0fa0acf5230.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Align stack pointer in unwinder dump

When printing the unwinder dump, the stack pointer could be unaligned,
for one of two reasons:

- stack corruption; or

- GCC created an unaligned stack.

There's no way for the unwinder to tell the difference between the two,
so we have to assume one or the other. GCC unaligned stacks are very
rare, and have only been spotted before GCC 5. Presumably, if we're
doing an unwinder stack dump, stack corruption is more likely than a
GCC unaligned stack. So always align the stack before starting the
dump.

Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2f540c515946ab09ed267e1a1d6421202a0cce08.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Use MSB for frame pointer encoding on 32-bit

On x86-32, Tetsuo Handa and Fengguang Wu reported unwinder warnings
like:

WARNING: kernel stack regs at f60bb9c8 in swapper:1 has bad 'bp' value 0ba00000

And also there were some stack dumps with a bunch of unreliable '?'
symbols after an apic_timer_interrupt symbol, meaning the unwinder got
confused when it tried to read the regs.

The cause of those issues is that, with GCC 4.8 (and possibly older),
there are cases where GCC misaligns the stack pointer in a leaf function
for no apparent reason:

c124a388 <acpi_rs_move_data>:
c124a388: 55 push %ebp
c124a389: 89 e5 mov %esp,%ebp
c124a38b: 57 push %edi
c124a38c: 56 push %esi
c124a38d: 89 d6 mov %edx,%esi
c124a38f: 53 push %ebx
c124a390: 31 db xor %ebx,%ebx
c124a392: 83 ec 03 sub $0x3,%esp
...
c124a3e3: 83 c4 03 add $0x3,%esp
c124a3e6: 5b pop %ebx
c124a3e7: 5e pop %esi
c124a3e8: 5f pop %edi
c124a3e9: 5d pop %ebp
c124a3ea: c3 ret

If an interrupt occurs in such a function, the regs on the stack will be
unaligned, which breaks the frame pointer encoding assumption. So on
32-bit, use the MSB instead of the LSB to encode the regs.

This isn't an issue on 64-bit, because interrupts align the stack before
writing to it.

Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/279a26996a482ca716605c7dbc7f2db9d8d91e81.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Fix dereference of untrusted pointer

Tetsuo Handa and Fengguang Wu reported a panic in the unwinder:

BUG: unable to handle kernel NULL pointer dereference at 000001f2
IP: update_stack_state+0xd4/0x340
*pde = 00000000

Oops: 0000 [#1] PREEMPT SMP
CPU: 0 PID: 18728 Comm: 01-cpu-hotplug Not tainted 4.13.0-rc4-00170-gb09be67 #592
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.9.3-20161025_171302-gandalf 04/01/2014
task: bb0b53c0 task.stack: bb3ac000
EIP: update_stack_state+0xd4/0x340
EFLAGS: 00010002 CPU: 0
EAX: 0000a570 EBX: bb3adccb ECX: 0000f401 EDX: 0000a570
ESI: 00000001 EDI: 000001ba EBP: bb3adc6b ESP: bb3adc3f
DS: 007b ES: 007b FS: 00d8 GS: 0000 SS: 0068
CR0: 80050033 CR2: 000001f2 CR3: 0b3a7000 CR4: 00140690
DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
DR6: fffe0ff0 DR7: 00000400
Call Trace:
? unwind_next_frame+0xea/0x400
? __unwind_start+0xf5/0x180
? __save_stack_trace+0x81/0x160
? save_stack_trace+0x20/0x30
? __lock_acquire+0xfa5/0x12f0
? lock_acquire+0x1c2/0x230
? tick_periodic+0x3a/0xf0
? _raw_spin_lock+0x42/0x50
? tick_periodic+0x3a/0xf0
? tick_periodic+0x3a/0xf0
? debug_smp_processor_id+0x12/0x20
? tick_handle_periodic+0x23/0xc0
? local_apic_timer_interrupt+0x63/0x70
? smp_trace_apic_timer_interrupt+0x235/0x6a0
? trace_apic_timer_interrupt+0x37/0x3c
? strrchr+0x23/0x50
Code: 0f 95 c1 89 c7 89 45 e4 0f b6 c1 89 c6 89 45 dc 8b 04 85 98 cb 74 bc 88 4d e3 89 45 f0 83 c0 01 84 c9 89 04 b5 98 cb 74 bc 74 3b <8b> 47 38 8b 57 34 c6 43 1d 01 25 00 00 02 00 83 e2 03 09 d0 83
EIP: update_stack_state+0xd4/0x340 SS:ESP: 0068:bb3adc3f
CR2: 00000000000001f2
---[ end trace 0d147fd4aba8ff50 ]---
Kernel panic - not syncing: Fatal exception in interrupt

On x86-32, after decoding a frame pointer to get a regs address,
regs_size() dereferences the regs pointer when it checks regs->cs to see
if the regs are user mode. This is dangerous because it's possible that
what looks like a decoded frame pointer is actually a corrupt value, and
we don't want the unwinder to make things worse.

Instead of calling regs_size() on an unsafe pointer, just assume they're
kernel regs to start with. Later, once it's safe to access the regs, we
can do the user mode check and corresponding safety check for the
remaining two regs.

Reported-and-tested-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Reported-and-tested-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: LKP <lkp@01.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 5ed8d8bb38c5 ("x86/unwind: Move common code into update_stack_state()")
Link: http://lkml.kernel.org/r/7f95b9a6993dec7674b3f3ab3dcd3294f7b9644d.1507597785.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

irq: Make the irqentry text section unconditional

Generate irqentry and softirqentry text sections without
any Kconfig dependencies. This will add extra sections, but
there should be no performace impact.

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David S . Miller <davem@davemloft.net>
Cc: Francis Deslauriers <francis.deslauriers@efficios.com>
Cc: Jesper Nilsson <jesper.nilsson@axis.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: linux-arch@vger.kernel.org
Cc: linux-cris-kernel@axis.com
Cc: mathieu.desnoyers@efficios.com
Link: http://lkml.kernel.org/r/150172789110.27216.3955739126693102122.stgit@devbox
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Add the ORC unwinder

Add the new ORC unwinder which is enabled by CONFIG_ORC_UNWINDER=y.
It plugs into the existing x86 unwinder framework.

It relies on objtool to generate the needed .orc_unwind and
.orc_unwind_ip sections.

For more details on why ORC is used instead of DWARF, see
Documentation/x86/orc-unwinder.txt - but the short version is
that it's a simplified, fundamentally more robust debugninfo
data structure, which also allows up to two orders of magnitude
faster lookups than the DWARF unwinder - which matters to
profiling workloads like perf.

Thanks to Andy Lutomirski for the performance improvement ideas:
splitting the ORC unwind table into two parallel arrays and creating a
fast lookup table to search a subset of the unwind table.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: live-patching@vger.kernel.org
Link: http://lkml.kernel.org/r/0a6cbfb40f8da99b7a45a1a8302dc6aef16ec812.1500938583.git.jpoimboe@redhat.com
[ Extended the changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Add end-of-stack check for ftrace handlers

Dave Jones and Steven Rostedt reported unwinder warnings like the
following:

WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8

In both cases, the unwinder was attempting to unwind from an ftrace
handler into entry code. The callchain was something like:

syscall entry code
C function
ftrace handler
save_stack_trace()

The problem is that the unwinder's end-of-stack logic gets confused by
the way ftrace lays out the stack frame (with fentry enabled).

I was able to recreate this warning with:

echo call_usermodehelper_exec_async:stacktrace > /sys/kernel/debug/tracing/set_ftrace_filter
(exit login session)

I considered fixing this by changing the ftrace code to rewrite the
stack to make the unwinder happy. But that seemed too intrusive after I
implemented it. Instead, just add another check to the unwinder's
end-of-stack logic to detect this special case.

Side note: We could probably get rid of these end-of-stack checks by
encoding the frame pointer for syscall entry just like we do for
interrupt entry. That would be simpler, but it would also be a lot more
intrusive since it would slightly affect the performance of every
syscall.

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: live-patching@vger.kernel.org
Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer")
Link: http://lkml.kernel.org/r/671ba22fbc0156b8f7e0cfa5ab2a795e08bc37e1.1495553739.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Dump all stacks in unwind_dump()

Currently unwind_dump() dumps only the most recently accessed stack.
But it has a few issues.

In some cases, 'first_sp' can get out of sync with 'stack_info', causing
unwind_dump() to start from the wrong address, flood the printk buffer,
and eventually read a bad address.

In other cases, dumping only the most recently accessed stack doesn't
give enough data to diagnose the error.

Fix both issues by dumping *all* stacks involved in the trace, not just
the last one.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 8b5e99f02264 ("x86/unwind: Dump stack data on warnings")
Link: http://lkml.kernel.org/r/016d6a9810d7d1bfc87ef8c0e6ee041c6744c909.1493171120.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Silence more entry-code related warnings

Borislav Petkov reported the following unwinder warning:

WARNING: kernel stack regs at ffffc9000024fea8 in udevadm:92 has bad 'bp' value 00007fffc4614d30
unwind stack type:0 next_sp: (null) mask:0x6 graph_idx:0
ffffc9000024fea8: 000055a6100e9b38 (0x55a6100e9b38)
ffffc9000024feb0: 000055a6100e9b35 (0x55a6100e9b35)
ffffc9000024feb8: 000055a6100e9f68 (0x55a6100e9f68)
ffffc9000024fec0: 000055a6100e9f50 (0x55a6100e9f50)
ffffc9000024fec8: 00007fffc4614d30 (0x7fffc4614d30)
ffffc9000024fed0: 000055a6100eaf50 (0x55a6100eaf50)
ffffc9000024fed8: 0000000000000000 ...
ffffc9000024fee0: 0000000000000100 (0x100)
ffffc9000024fee8: ffff8801187df488 (0xffff8801187df488)
ffffc9000024fef0: 00007ffffffff000 (0x7ffffffff000)
ffffc9000024fef8: 0000000000000000 ...
ffffc9000024ff10: ffffc9000024fe98 (0xffffc9000024fe98)
ffffc9000024ff18: 00007fffc4614d00 (0x7fffc4614d00)
ffffc9000024ff20: ffffffffffffff10 (0xffffffffffffff10)
ffffc9000024ff28: ffffffff811c6c1f (SyS_newlstat+0xf/0x10)
ffffc9000024ff30: 0000000000000010 (0x10)
ffffc9000024ff38: 0000000000000296 (0x296)
ffffc9000024ff40: ffffc9000024ff50 (0xffffc9000024ff50)
ffffc9000024ff48: 0000000000000018 (0x18)
ffffc9000024ff50: ffffffff816b2e6a (entry_SYSCALL_64_fastpath+0x18/0xa8)
...

It unwinded from an interrupt which came in right after entry code
called into a C syscall handler, before it had a chance to set up the
frame pointer, so regs->bp still had its user space value.

Add a check to silence warnings in such a case, where an interrupt
has occurred and regs->sp is almost at the end of the stack.

Reported-by: Borislav Petkov <bp@suse.de>
Tested-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer")
Link: http://lkml.kernel.org/r/c695f0d0d4c2cfe6542b90e2d0520e11eb901eb5.1493171120.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Remove unused 'sp' parameter in unwind_dump()

The 'sp' parameter to unwind_dump() is unused. Remove it.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/08cb36b004629f6bbcf44c267ae4a609242ebd0b.1492520933.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Prepend hex mask value with '0x' in unwind_dump()

In unwind_dump(), the stack mask value is printed in hex, but is
confusingly not prepended with '0x'.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/e7fe41be19d73c9f99f53082486473febfe08ffa.1492520933.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Properly zero-pad 32-bit values in unwind_dump()

On x86-32, 32-bit stack values printed by unwind_dump() are confusingly
zero-padded to 16 characters (64 bits):

unwind stack type:0 next_sp: (null) mask:a graph_idx:0
f50cdebc: 00000000f50cdec4 (0xf50cdec4)
f50cdec0: 00000000c40489b7 (irq_exit+0x87/0xa0)
...

Instead, base the field width on the size of a long integer so that it
looks right on both x86-32 and x86-64.

x86-32:

unwind stack type:1 next_sp: (null) mask:0x2 graph_idx:0
c0ee9d98: c0ee9de0 (init_thread_union+0x1de0/0x2000)
c0ee9d9c: c043fd90 (__save_stack_trace+0x50/0xe0)
...

x86-64:

unwind stack type:1 next_sp: (null) mask:0x2 graph_idx:0
ffffffff81e03b88: ffffffff81e03c10 (init_thread_union+0x3c10/0x4000)
ffffffff81e03b90: ffffffff81048f8e (__save_stack_trace+0x5e/0x100)
...

Reported-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/36b743812e7eb291d74af4e5067736736622daad.1492520933.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Silence entry-related warnings

A few people have reported unwinder warnings like the following:

WARNING: kernel stack frame pointer at ffffc90000fe7ff0 in rsync:1157 has bad value (null)
unwind stack type:0 next_sp: (null) mask:2 graph_idx:0
ffffc90000fe7f98: ffffc90000fe7ff0 (0xffffc90000fe7ff0)
ffffc90000fe7fa0: ffffffffb7000f56 (trace_hardirqs_off_thunk+0x1a/0x1c)
ffffc90000fe7fa8: 0000000000000246 (0x246)
ffffc90000fe7fb0: 0000000000000000 ...
ffffc90000fe7fc0: 00007ffe3af639bc (0x7ffe3af639bc)
ffffc90000fe7fc8: 0000000000000006 (0x6)
ffffc90000fe7fd0: 00007f80af433fc5 (0x7f80af433fc5)
ffffc90000fe7fd8: 00007ffe3af638e0 (0x7ffe3af638e0)
ffffc90000fe7fe0: 00007ffe3af638e0 (0x7ffe3af638e0)
ffffc90000fe7fe8: 00007ffe3af63970 (0x7ffe3af63970)
ffffc90000fe7ff0: 0000000000000000 ...
ffffc90000fe7ff8: ffffffffb7b74b9a (entry_SYSCALL_64_after_swapgs+0x17/0x4f)

This warning can happen when unwinding a code path where an interrupt
occurred in x86 entry code before it set up the first stack frame.
Silently ignore any warnings for this case.

Reported-by: Daniel Borkmann <daniel@iogearbox.net>
Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer")
Link: http://lkml.kernel.org/r/dbd6838826466a60dc23a52098185bc973ce2f1e.1492020577.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Read stack return address in update_stack_state()

Instead of reading the return address when unwind_get_return_address()
is called, read it from update_stack_state() and store it in the unwind
state. This enables the next patch to check the return address from
unwind_next_frame() so it can detect an entry code frame.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/af0c5e4560c49c0343dca486ea26c4fa92bc4e35.1492020577.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Move common code into update_stack_state()

The __unwind_start() and unwind_next_frame() functions have some
duplicated functionality. They both call decode_frame_pointer() and set
state->regs and state->bp accordingly. Move that functionality to a
common place in update_stack_state().

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/a2ee4801113f6d2300d58f08f6b69f85edf4eb43.1492020577.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Fix last frame check for aligned function stacks

Pavel Machek reported the following warning on x86-32:

WARNING: kernel stack frame pointer at f50cdf98 in swapper/2:0 has bad value (null)

The warning is caused by the unwinder not realizing that it reached the
end of the stack, due to an unusual prologue which gcc sometimes
generates for aligned stacks. The prologue is based on a gcc feature
called the Dynamic Realign Argument Pointer (DRAP). It's almost always
enabled for aligned stacks when -maccumulate-outgoing-args isn't set.

This issue is similar to the one fixed by the following commit:

8023e0e2a48d ("x86/unwind: Adjust last frame check for aligned function stacks")

... but that fix was specific to x86-64.

Make the fix more generic to cover x86-32 as well, and also ensure that
the return address referred to by the frame pointer is a copy of the
original return address.

Fixes: acb4608ad186 ("x86/unwind: Create stack frames for saved syscall registers")
Reported-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/50d4924db716c264b14f1633037385ec80bf89d2.1489465609.git.jpoimboe@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

stacktrace/x86: add function for detecting reliable stack traces

For live patching and possibly other use cases, a stack trace is only
useful if it can be assured that it's completely reliable. Add a new
save_stack_trace_tsk_reliable() function to achieve that.

Note that if the target task isn't the current task, and the target task
is allowed to run, then it could be writing the stack while the unwinder
is reading it, resulting in possible corruption. So the caller of
save_stack_trace_tsk_reliable() must ensure that the task is either
'current' or inactive.

save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection
of pt_regs on the stack. If the pt_regs are not user-mode registers
from a syscall, then they indicate an in-kernel interrupt or exception
(e.g. preemption or a page fault), in which case the stack is considered
unreliable due to the nature of frame pointers.

It also relies on the x86 unwinder's detection of other issues, such as:

- corrupted stack data
- stack grows the wrong way
- stack walk doesn't reach the bottom
- user didn't provide a large enough entries array

Such issues are reported by checking unwind_error() and !unwind_done().

Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can
determine at build time whether the function is implemented.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Reviewed-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Ingo Molnar <mingo@kernel.org> # for the x86 changes
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task_stack.h>

We are going to split <linux/sched/task_stack.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task_stack.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

sched/headers: Prepare for new header dependencies before moving code to <linux/sched/task.h>

We are going to split <linux/sched/task.h> out of <linux/sched.h>, which
will have to be picked up from other headers and a couple of .c files.

Create a trivial placeholder <linux/sched/task.h> file that just
maps to <linux/sched.h> to make this patch obviously correct and
bisectable.

Include the new header in the files that are going to need it.

Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Disable KASAN checks for non-current tasks

There are a handful of callers to save_stack_trace_tsk() and
show_stack() which try to unwind the stack of a task other than current.
In such cases, it's remotely possible that the task is running on one
CPU while the unwinder is reading its stack from another CPU, causing
the unwinder to see stack corruption.

These cases seem to be mostly harmless. The unwinder has checks which
prevent it from following bad pointers beyond the bounds of the stack.
So it's not really a bug as long as the caller understands that
unwinding another task will not always succeed.

In such cases, it's possible that the unwinder may read a KASAN-poisoned
region of the stack. Account for that by using READ_ONCE_NOCHECK() when
reading the stack of another task.

Use READ_ONCE() when reading the stack of the current task, since KASAN
warnings can still be useful for finding bugs in that case.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Jones <davej@codemonkey.org.uk>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/4c575eb288ba9f73d498dfe0acde2f58674598f1.1483978430.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Silence warnings for non-current tasks

There are a handful of callers to save_stack_trace_tsk() and
show_stack() which try to unwind the stack of a task other than current.
In such cases, it's remotely possible that the task is running on one
CPU while the unwinder is reading its stack from another CPU, causing
the unwinder to see stack corruption.

These cases seem to be mostly harmless. The unwinder has checks which
prevent it from following bad pointers beyond the bounds of the stack.
So it's not really a bug as long as the caller understands that
unwinding another task will not always succeed.

Since stack "corruption" on another task's stack isn't necessarily a
bug, silence the warnings when unwinding tasks other than current.

Reported-by: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Miroslav Benes <mbenes@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/00d8c50eea3446c1524a2a755397a3966629354c.1483978430.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

Revert "x86/unwind: Detect bad stack return address"

Revert the following commit:

b6959a362177 ("x86/unwind: Detect bad stack return address")

... because Andrey Konovalov reported an unwinder warning:

WARNING: unrecognized kernel stack return address ffffffffa0000001 at ffff88006377fa18 in a.out:4467

The unwind was initiated from an interrupt which occurred while running in the
generated code for a kprobe. The unwinder printed the warning because it
expected regs->ip to point to a valid text address, but instead it pointed to
the generated code.

Eventually we may want come up with a way to identify generated kprobe
code so the unwinder can know that it's a valid return address. Until
then, just remove the warning.

Reported-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/02f296848fbf49fb72dfeea706413ecbd9d4caf6.1482418739.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Dump stack data on warnings

The unwinder warnings are good at finding unexpected unwinder issues,
but they often don't give enough data to be able to fully diagnose them.
Print a one-time stack dump when a warning is detected.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/15607370e3ddb1732b6a73d5c65937864df16ac8.1481904011.git.jpoimboe@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

x86/unwind: Adjust last frame check for aligned function stacks

Somehow, CONFIG_PARAVIRT=n convinces gcc to change the
x86_64_start_kernel() prologue from:

0000000000000129 <x86_64_start_kernel>:
129: 55 push %rbp
12a: 48 89 e5 mov %rsp,%rbp

to:

0000000000000124 <x86_64_start_kernel>:
124: 4c 8d 54 24 08 lea 0x8(%rsp),%r10
129: 48 83 e4 f0 and $0xfffffffffffffff0,%rsp
12d: 41 ff 72 f8 pushq -0x8(%r10)
131: 55 push %rbp
132: 48 89 e5 mov %rsp,%rbp

This is an unusual pattern which aligns rsp (though in this case it's
already aligned) and saves the start_cpu() return address again on the
stack before storing the frame pointer.

The unwinder assumes the last stack frame header is at a certain offset,
but the above code breaks that assumption, resulting in the following
warning:

WARNING: kernel stack frame pointer at ffffffff82e03f40 in swapper:0 has bad value (null)

Fix it by checking for the last task stack frame at the aligned offset
in addition to the normal unaligned offset.

Fixes: acb4608ad186 ("x86/unwind: Create stack frames for saved syscall registers")
Reported-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/9d7b4eb8cf55a7d6002cb738f25c23e7429c99a0.1481904011.git.jpoimboe@redhat.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

x86/unwind: Ensure stack grows down

Add a sanity check to ensure the stack only grows down, and print a
warning if the check fails.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20161027131058.tpdffwlqipv7pcd6@treble
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Detect bad stack return address

If __kernel_text_address() doesn't recognize a return address on the
stack, it probably means that it's some generated code which
__kernel_text_address() doesn't know about yet.

Otherwise there's probably some stack corruption.

Either way, warn about it.

Use printk_deferred_once() because the unwinder can be called with the
console lock by lockdep via save_stack_trace().

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/2d897898f324e275943b590d160b55e482bba65f.1477496147.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Warn on bad frame pointer

Detect situations in the unwinder where the frame pointer refers to a
bad address, and print an appropriate warning.

Use printk_deferred_once() because the unwinder can be called with the
console lock by lockdep via save_stack_trace().

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/03c888f6f7414d54fa56b393ea25482be6899b5f.1477496147.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Create stack frames for saved syscall registers

The entry code doesn't encode the pt_regs pointer for syscalls. But the
pt_regs are always at the same location, so we can add a manual check
for them.

A later patch prints them as part of the oops stack dump. They could be
useful, for example, to determine the arguments to a system call.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/e176aa9272930cd3f51fda0b94e2eae356677da4.1476973742.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/entry/unwind: Create stack frames for saved interrupt registers

With frame pointers, when a task is interrupted, its stack is no longer
completely reliable because the function could have been interrupted
before it had a chance to save the previous frame pointer on the stack.
So the caller of the interrupted function could get skipped by a stack
trace.

This is problematic for live patching, which needs to know whether a
stack trace of a sleeping task can be relied upon. There's currently no
way to detect if a sleeping task was interrupted by a page fault
exception or preemption before it went to sleep.

Another issue is that when dumping the stack of an interrupted task, the
unwinder has no way of knowing where the saved pt_regs registers are, so
it can't print them.

This solves those issues by encoding the pt_regs pointer in the frame
pointer on entry from an interrupt or an exception.

This patch also updates the unwinder to be able to decode it, because
otherwise the unwinder would be broken by this change.

Note that this causes a change in the behavior of the unwinder: each
instance of a pt_regs on the stack is now considered a "frame". So
callers of unwind_get_return_address() will now get an occasional
'regs->ip' address that would have previously been skipped over.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/8b9f84a21e39d249049e0547b559ff8da0df0988.1476973742.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

x86/unwind: Add new unwind interface and implementations

The x86 stack dump code is a bit of a mess. dump_trace() uses
callbacks, and each user of it seems to have slightly different
requirements, so there are several slightly different callbacks floating
around.

Also there are some upcoming features which will need more changes to
the stack dump code, including the printing of stack pt_regs, reliable
stack detection for live patching, and a DWARF unwinder. Each of those
features would at least need more callbacks and/or callback interfaces,
resulting in a much bigger mess than what we have today.

Before doing all that, we should try to clean things up and replace
dump_trace() with something cleaner and more flexible.

The new unwinder is a simple state machine which was heavily inspired by
a suggestion from Andy Lutomirski:

https://lkml.kernel.org/r/CALCETrUbNTqaM2LRyXGRx=kVLRPeY5A3Pc6k4TtQxF320rUT=w@mail.gmail.com

It's also similar to the libunwind API:

http://www.nongnu.org/libunwind/man/libunwind(3).html

Some if its advantages:

- Simplicity: no more callback sprawl and less code duplication.

- Flexibility: it allows the caller to stop and inspect the stack state
at each step in the unwinding process.

- Modularity: the unwinder code, console stack dump code, and stack
metadata analysis code are all better separated so that changing one
of them shouldn't have much of an impact on any of the others.

Two implementations are added which conform to the new unwind interface:

- The frame pointer unwinder which is used for CONFIG_FRAME_POINTER=y.

- The "guess" unwinder which is used for CONFIG_FRAME_POINTER=n. This
isn't an "unwinder" per se. All it does is scan the stack for kernel
text addresses. But with no frame pointers, guesses are better than
nothing in most cases.

Suggested-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Byungchul Park <byungchul.park@lge.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nilay Vaish <nilayvaish@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/6dc2f909c47533d213d0505f0a113e64585bec82.1474045023.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>