cfi: Add CFI_NOSEAL()

Add a CFI_NOSEAL() helper to mark functions that need to retain their
CFI information, despite not otherwise leaking their address.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231215092707.669401084@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

x86/cfi,bpf: Fix bpf_struct_ops CFI

BPF struct_ops uses __arch_prepare_bpf_trampoline() to write
trampolines for indirect function calls. These tramplines much have
matching CFI.

In order to obtain the correct CFI hash for the various methods, add a
matching structure that contains stub functions, the compiler will
generate correct CFI which we can pilfer for the trampolines.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231215092707.566977112@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

x86/cfi,bpf: Fix bpf_callback_t CFI

Where the main BPF program is expected to match bpf_func_t,
sub-programs are expected to match bpf_callback_t.

This fixes things like:

tools/testing/selftests/bpf/progs/bloom_filter_bench.c:

bpf_for_each_map_elem(&array_map, bloom_callback, &data, 0);

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231215092707.451956710@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

x86/cfi,bpf: Fix BPF JIT call

The current BPF call convention is __nocfi, except when it calls !JIT things,
then it calls regular C functions.

It so happens that with FineIBT the __nocfi and C calling conventions are
incompatible. Specifically __nocfi will call at func+0, while FineIBT will have
endbr-poison there, which is not a valid indirect target. Causing #CP.

Notably this only triggers on IBT enabled hardware, which is probably why this
hasn't been reported (also, most people will have JIT on anyway).

Implement proper CFI prologues for the BPF JIT codegen and drop __nocfi for
x86.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20231215092707.345270396@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

cfi: Flip headers

Normal include order is that linux/foo.h should include asm/foo.h, CFI has it
the wrong way around.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Sami Tolvanen <samitolvanen@google.com>
Link: https://lore.kernel.org/r/20231215092707.231038174@infradead.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

x86: Add support for CONFIG_CFI_CLANG

With CONFIG_CFI_CLANG, the compiler injects a type preamble immediately
before each function and a check to validate the target function type
before indirect calls:

; type preamble
__cfi_function:
mov <id>, %eax
function:
...
; indirect call check
mov -<id>,%r10d
add -0x4(%r11),%r10d
je .Ltmp1
ud2
.Ltmp1:
call __x86_indirect_thunk_r11

Add error handling code for the ud2 traps emitted for the checks, and
allow CONFIG_CFI_CLANG to be selected on x86_64.

This produces the following oops on CFI failure (generated using lkdtm):

[ 21.441706] CFI failure at lkdtm_indirect_call+0x16/0x20 [lkdtm]
(target: lkdtm_increment_int+0x0/0x10 [lkdtm]; expected type: 0x7e0c52a)
[ 21.444579] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
[ 21.445296] CPU: 0 PID: 132 Comm: sh Not tainted
5.19.0-rc8-00020-g9f27360e674c #1
[ 21.445296] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.14.0-0-g155821a1990b-prebuilt.qemu.org 04/01/2014
[ 21.445296] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm]
[ 21.445296] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f
44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8
[ 21.445296] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292
[ 21.445296] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700
[ 21.445296] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450
[ 21.445296] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610
[ 21.445296] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000
[ 21.445296] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002
[ 21.445296] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000)
knlGS:0000000000000000
[ 21.445296] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 21.445296] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0
[ 21.445296] Call Trace:
[ 21.445296] <TASK>
[ 21.445296] lkdtm_CFI_FORWARD_PROTO+0x30/0x50 [lkdtm]
[ 21.445296] direct_entry+0x12d/0x140 [lkdtm]
[ 21.445296] full_proxy_write+0x5d/0xb0
[ 21.445296] vfs_write+0x144/0x460
[ 21.445296] ? __x64_sys_wait4+0x5a/0xc0
[ 21.445296] ksys_write+0x69/0xd0
[ 21.445296] do_syscall_64+0x51/0xa0
[ 21.445296] entry_SYSCALL_64_after_hwframe+0x63/0xcd
[ 21.445296] RIP: 0033:0x7f08b41a6fe1
[ 21.445296] Code: be 07 00 00 00 41 89 c0 e8 7e ff ff ff 44 89 c7 89
04 24 e8 91 c6 02 00 8b 04 24 48 83 c4 68 c3 48 63 ff b8 01 00 00 03
[ 21.445296] RSP: 002b:00007ffcdf65c2e8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 21.445296] RAX: ffffffffffffffda RBX: 00007f08b4221690 RCX: 00007f08b41a6fe1
[ 21.445296] RDX: 0000000000000012 RSI: 0000000000c738f0 RDI: 0000000000000001
[ 21.445296] RBP: 0000000000000001 R08: fefefefefefefeff R09: fefefefeffc5ff4e
[ 21.445296] R10: 00007f08b42222b0 R11: 0000000000000246 R12: 0000000000c738f0
[ 21.445296] R13: 0000000000000012 R14: 00007ffcdf65c401 R15: 0000000000c70450
[ 21.445296] </TASK>
[ 21.445296] Modules linked in: lkdtm
[ 21.445296] Dumping ftrace buffer:
[ 21.445296] (ftrace buffer empty)
[ 21.471442] ---[ end trace 0000000000000000 ]---
[ 21.471811] RIP: 0010:lkdtm_indirect_call+0x16/0x20 [lkdtm]
[ 21.472467] Code: 52 1c c0 48 c7 c1 c5 50 1c c0 e9 25 48 2a cc 0f 1f
44 00 00 49 89 fb 48 c7 c7 50 b4 1c c0 41 ba 5b ad f3 81 45 03 53 f8
[ 21.474400] RSP: 0018:ffffa9f9c02ffdc0 EFLAGS: 00000292
[ 21.474735] RAX: 0000000000000027 RBX: ffffffffc01cb300 RCX: 385cbbd2e070a700
[ 21.475664] RDX: 0000000000000000 RSI: c0000000ffffdfff RDI: ffffffffc01cb450
[ 21.476471] RBP: 0000000000000006 R08: 0000000000000000 R09: ffffffff8d081610
[ 21.477127] R10: 00000000bcc90825 R11: ffffffffc01c2fc0 R12: 0000000000000000
[ 21.477959] R13: ffffa31b827a6000 R14: 0000000000000000 R15: 0000000000000002
[ 21.478657] FS: 00007f08b42216a0(0000) GS:ffffa31b9f400000(0000)
knlGS:0000000000000000
[ 21.479577] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 21.480307] CR2: 0000000000c76678 CR3: 0000000001940000 CR4: 00000000000006f0
[ 21.481460] Kernel panic - not syncing: Fatal exception

Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Kees Cook <keescook@chromium.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220908215504.3686827-23-samitolvanen@google.com