Re: [PATCH bpf-next v3 1/4] bpf: crypto: Use the correct destructor kfunc type

[Viktor Malik <vmalik@redhat.com>]

On 7/28/25 22:26, Sami Tolvanen wrote:
> With CONFIG_CFI_CLANG enabled, the kernel strictly enforces that
> indirect function calls use a function pointer type that matches the
> target function. I ran into the following type mismatch when running
> BPF self-tests:
> 
>   CFI failure at bpf_obj_free_fields+0x190/0x238 (target:
>     bpf_crypto_ctx_release+0x0/0x94; expected type: 0xa488ebfc)
>   Internal error: Oops - CFI: 00000000f2008228 [#1]  SMP
>   ...
> 
> As bpf_crypto_ctx_release() is also used in BPF programs and using
> a void pointer as the argument would make the verifier unhappy, add
> a simple stub function with the correct type and register it as the
> destructor kfunc instead.

Hi,

this patchset got somehow forgotten and I'd like to revive it.

We're hitting kernel oops when running the crypto cases from test_progs
(`./test_progs -t crypto`) on CPUs with IBT (Indirect Branch Tracking)
support. I managed to reproduce this on the latest bpf-next, see the
relevant part of dmesg at the end of this email.

After applying this patch, the oops no longer happens.

It looks like the series is stuck on a sparse warning reported by kernel
test robot, which seems like a false positive. Could we somehow resolve
it and proceed with reviewing and merging this?

Since this resolves our issue, adding my tested-by:

Tested-by: Viktor Malik <vmalik@redhat.com>

Thanks!
Viktor

The relevant part of dmesg:

    [ 1505.054762] Missing ENDBR: bpf_crypto_ctx_release+0x0/0x50 
    [ 1505.060306] ------------[ cut here ]------------ 
    [ 1505.064971] kernel BUG at arch/x86/kernel/cet.c:133! 
    [ 1505.069984] Oops: invalid opcode: 0000 [#1] SMP NOPTI 
    [ 1505.075085] CPU: 129 UID: 0 PID: 42861 Comm: kworker/u688:24 Tainted: G           OE       6.18.0-rc5+ #3 PREEMPT(voluntary)  
    [ 1505.086437] Tainted: [O]=OOT_MODULE, [E]=UNSIGNED_MODULE 
    [ 1505.091794] Hardware name: Intel Corporation GNR-WS/GNR-WS, BIOS GWS_REL1.IPC.3663.P19.2506271437 06/27/2025 
    [ 1505.101674] Workqueue: events_unbound bpf_map_free_deferred 
    [ 1505.107291] RIP: 0010:exc_control_protection+0x19a/0x1a0 
    [ 1505.112648] Code: d8 b9 09 00 00 00 48 8b 93 80 00 00 00 be 81 00 00 00 48 c7 c7 53 09 b2 a0 e8 c2 74 1c ff 80 a3 8a 00 00 00 fb e9 fb fe ff ff <0f> 0b 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 
    [ 1505.131474] RSP: 0018:ff714c596fe17ce8 EFLAGS: 00010002 
    [ 1505.136742] RAX: 000000000000002e RBX: ff714c596fe17d08 RCX: 0000000000000000 
    [ 1505.143924] RDX: 0000000000000000 RSI: 0000000000000001 RDI: ff2a470fbe458240 
    [ 1505.151111] RBP: 0000000000000003 R08: 0000000000000000 R09: ff714c596fe17b70 
    [ 1505.158293] R10: ff2a470fbc07ffa8 R11: 0000000000000003 R12: 0000000000000000 
    [ 1505.165478] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000 
    [ 1505.172661] FS:  0000000000000000(0000) GS:ff2a47101c091000(0000) knlGS:0000000000000000 
    [ 1505.180805] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033 
    [ 1505.186600] CR2: 00005564968dd250 CR3: 0000001e45a22005 CR4: 0000000000f73ef0 
    [ 1505.193782] PKRU: 55555554 
    [ 1505.196533] Call Trace: 
    [ 1505.199026]  <TASK> 
    [ 1505.201171]  asm_exc_control_protection+0x26/0x60 
    [ 1505.205923] RIP: 0010:bpf_crypto_ctx_release+0x0/0x50 
    [ 1505.211023] Code: 00 eb ee 89 c2 eb d7 31 c0 5b c3 cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 <0f> 1f 40 d6 0f 1f 44 00 00 48 8d 57 28 b8 ff ff ff ff f0 0f c1 47 
    [ 1505.229849] RSP: 0018:ff714c596fe17db8 EFLAGS: 00010202 
    [ 1505.235118] RAX: ffffffff9f7917d0 RBX: ff2a46f0ce98cc20 RCX: 000000008200019e 
    [ 1505.242301] RDX: 0000000000000001 RSI: ff2a46f0dd55ff30 RDI: ff2a46f0e8662280 
    [ 1505.249483] RBP: ff2a46f0ce98cc20 R08: 0000000000000000 R09: 0000000000000001 
    [ 1505.256666] R10: 000000008200019e R11: ff2a46f0c5573bc8 R12: 0000000000000000 
    [ 1505.263849] R13: ff2a46f0ce98cc00 R14: ff2a46f0dd55ff30 R15: ff2a46f0e8662280 
    [ 1505.271035]  ? __pfx_bpf_crypto_ctx_release+0x10/0x10 
    [ 1505.276135]  bpf_obj_free_fields+0x10c/0x230 
    [ 1505.280451]  array_map_free+0x56/0x140 
    [ 1505.284243]  bpf_map_free_deferred+0x95/0x180 
    [ 1505.288646]  process_one_work+0x18b/0x340 
    [ 1505.292705]  worker_thread+0x256/0x3a0 
    [ 1505.296497]  ? __pfx_worker_thread+0x10/0x10 
    [ 1505.300813]  kthread+0xfc/0x240 
    [ 1505.304000]  ? __pfx_kthread+0x10/0x10 
    [ 1505.307792]  ? __pfx_kthread+0x10/0x10 
    [ 1505.311584]  ret_from_fork+0xf0/0x110 
    [ 1505.315297]  ? __pfx_kthread+0x10/0x10 
    [ 1505.319089]  ret_from_fork_asm+0x1a/0x30 
    [ 1505.323059]  </TASK> 

> 
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> ---
>  kernel/bpf/crypto.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
> index 94854cd9c4cc..a267d9087d40 100644
> --- a/kernel/bpf/crypto.c
> +++ b/kernel/bpf/crypto.c
> @@ -261,6 +261,12 @@ __bpf_kfunc void bpf_crypto_ctx_release(struct bpf_crypto_ctx *ctx)
>  		call_rcu(&ctx->rcu, crypto_free_cb);
>  }
>  
> +__bpf_kfunc void bpf_crypto_ctx_release_dtor(void *ctx)
> +{
> +	bpf_crypto_ctx_release(ctx);
> +}
> +CFI_NOSEAL(bpf_crypto_ctx_release_dtor);
> +
>  static int bpf_crypto_crypt(const struct bpf_crypto_ctx *ctx,
>  			    const struct bpf_dynptr_kern *src,
>  			    const struct bpf_dynptr_kern *dst,
> @@ -368,7 +374,7 @@ static const struct btf_kfunc_id_set crypt_kfunc_set = {
>  
>  BTF_ID_LIST(bpf_crypto_dtor_ids)
>  BTF_ID(struct, bpf_crypto_ctx)
> -BTF_ID(func, bpf_crypto_ctx_release)
> +BTF_ID(func, bpf_crypto_ctx_release_dtor)
>  
>  static int __init crypto_kfunc_init(void)
>  {