selftests/bpf: Move kfunc exports to bpf_testmod/bpf_testmod_kfunc.h

Move all kfunc exports into separate bpf_testmod_kfunc.h header file
and include it in tests that need it.

We will move all test kfuncs into bpf_testmod in following change,
so it's convenient to have declarations in single place.

The bpf_testmod_kfunc.h is included by both bpf_testmod and bpf
programs that use test kfuncs.

As suggested by David, the bpf_testmod_kfunc.h includes vmlinux.h
and bpf/bpf_helpers.h for bpf programs build, so the declarations
have proper __ksym attribute and we can resolve all the structs.

Note in kfunc_call_test_subprog.c we can no longer use the sk_state
define from bpf_tcp_helpers.h (because it clashed with vmlinux.h)
and we need to address __sk_common.skc_state field directly.

Acked-by: David Vernet <void@manifault.com>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Link: https://lore.kernel.org/r/20230515133756.1658301-3-jolsa@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

selftests/bpf: Add test for race in btf_try_get_module

This adds a complete test case to ensure we never take references to
modules not in MODULE_STATE_LIVE, which can lead to UAF, and it also
ensures we never access btf->kfunc_set_tab in an inconsistent state.

The test uses userfaultfd to artificially widen the race.

When run on an unpatched kernel, it leads to the following splat:

[root@(none) bpf]# ./test_progs -t bpf_mod_race/ksym
[ 55.498171] BUG: unable to handle page fault for address: fffffbfff802548b
[ 55.499206] #PF: supervisor read access in kernel mode
[ 55.499855] #PF: error_code(0x0000) - not-present page
[ 55.500555] PGD a4fa9067 P4D a4fa9067 PUD a4fa5067 PMD 1b44067 PTE 0
[ 55.501499] Oops: 0000 [#1] PREEMPT SMP KASAN NOPTI
[ 55.502195] CPU: 0 PID: 83 Comm: kworker/0:2 Tainted: G OE 5.16.0-rc4+ #151
[ 55.503388] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ArchLinux 1.15.0-1 04/01/2014
[ 55.504777] Workqueue: events bpf_prog_free_deferred
[ 55.505563] RIP: 0010:kasan_check_range+0x184/0x1d0
[ 55.509140] RSP: 0018:ffff88800560fcf0 EFLAGS: 00010282
[ 55.509977] RAX: fffffbfff802548b RBX: fffffbfff802548c RCX: ffffffff9337b6ba
[ 55.511096] RDX: fffffbfff802548c RSI: 0000000000000004 RDI: ffffffffc012a458
[ 55.512143] RBP: fffffbfff802548b R08: 0000000000000001 R09: ffffffffc012a45b
[ 55.513228] R10: fffffbfff802548b R11: 0000000000000001 R12: ffff888001b5f598
[ 55.514332] R13: ffff888004f49ac8 R14: 0000000000000000 R15: ffff888092449400
[ 55.515418] FS: 0000000000000000(0000) GS:ffff888092400000(0000) knlGS:0000000000000000
[ 55.516705] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 55.517560] CR2: fffffbfff802548b CR3: 0000000007c10006 CR4: 0000000000770ef0
[ 55.518672] PKRU: 55555554
[ 55.519022] Call Trace:
[ 55.519483] <TASK>
[ 55.519884] module_put.part.0+0x2a/0x180
[ 55.520642] bpf_prog_free_deferred+0x129/0x2e0
[ 55.521478] process_one_work+0x4fa/0x9e0
[ 55.522122] ? pwq_dec_nr_in_flight+0x100/0x100
[ 55.522878] ? rwlock_bug.part.0+0x60/0x60
[ 55.523551] worker_thread+0x2eb/0x700
[ 55.524176] ? __kthread_parkme+0xd8/0xf0
[ 55.524853] ? process_one_work+0x9e0/0x9e0
[ 55.525544] kthread+0x23a/0x270
[ 55.526088] ? set_kthread_struct+0x80/0x80
[ 55.526798] ret_from_fork+0x1f/0x30
[ 55.527413] </TASK>
[ 55.527813] Modules linked in: bpf_testmod(OE) [last unloaded: bpf_testmod]
[ 55.530846] CR2: fffffbfff802548b
[ 55.531341] ---[ end trace 1af41803c054ad6d ]---
[ 55.532136] RIP: 0010:kasan_check_range+0x184/0x1d0
[ 55.535887] RSP: 0018:ffff88800560fcf0 EFLAGS: 00010282
[ 55.536711] RAX: fffffbfff802548b RBX: fffffbfff802548c RCX: ffffffff9337b6ba
[ 55.537821] RDX: fffffbfff802548c RSI: 0000000000000004 RDI: ffffffffc012a458
[ 55.538899] RBP: fffffbfff802548b R08: 0000000000000001 R09: ffffffffc012a45b
[ 55.539928] R10: fffffbfff802548b R11: 0000000000000001 R12: ffff888001b5f598
[ 55.541021] R13: ffff888004f49ac8 R14: 0000000000000000 R15: ffff888092449400
[ 55.542108] FS: 0000000000000000(0000) GS:ffff888092400000(0000) knlGS:0000000000000000
[ 55.543260]CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 55.544136] CR2: fffffbfff802548b CR3: 0000000007c10006 CR4: 0000000000770ef0
[ 55.545317] PKRU: 55555554
[ 55.545671] note: kworker/0:2[83] exited with preempt_count 1

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220114163953.1455836-11-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>