Re: [PATCH] crypto: ahash - Stop legacy tfms from using the set_virt fallback path

[Eric Biggers <ebiggers@kernel.org>]

On Fri, Jun 13, 2025 at 04:51:38PM +0800, Herbert Xu wrote:
> On Thu, Jun 12, 2025 at 10:54:39PM -0700, Eric Biggers wrote:
> >
> > Actually, crypto_ahash::base::fb is initialized if CRYPTO_ALG_NEED_FALLBACK,
> > which many of the drivers already set.  Then crypto_ahash_update() calls
> > ahash_do_req_chain() if the algorithm does *not* have
> > CRYPTO_AHASH_ALG_BLOCK_ONLY set.  Which then exports the driver's custom state
> > and tries to import it into the fallback.
> > 
> > As far as I can tell, it's just broken for most of the existing drivers.
> 
> This fallback path is only meant to be used for drivers that have
> been converted.  But you're right there is a check missing in there.
> 
> Thanks,
> 
> ---8<---
> Ensure that drivers that have not been converted to the ahash API
> do not use the ahash_request_set_virt fallback path as they cannot
> use the software fallback.
> 
> Reported-by: Eric Biggers <ebiggers@kernel.org>
> Fixes: 9d7a0ab1c753 ("crypto: ahash - Handle partial blocks in API")
> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

Okay.  Out of curiosity I decided to actually test the Qualcomm Crypto Engine
driver on a development board that has a Qualcomm SoC, using latest mainline.

Even with your patch applied, it overflows the stack when running the crypto
self-tests, apparently due to crypto/ahash.c calling into itself recursively:

    [    9.230887] Insufficient stack space to handle exception!
    [    9.230889] ESR: 0x0000000096000047 -- DABT (current EL)
    [    9.230891] FAR: 0xffff800084927fe0
    [    9.230891] Task stack:     [0xffff800084928000..0xffff80008492c000]
    [    9.230893] IRQ stack:      [0xffff800080030000..0xffff800080034000]
    [    9.230894] Overflow stack: [0xffff000a72dd2100..0xffff000a72dd3100]
    [    9.230896] CPU: 6 UID: 0 PID: 747 Comm: cryptomgr_test Tainted: G S                  6.16.0-rc1-00237-g84ffcd88616f #7 PREEMPT 
    [    9.230900] Tainted: [S]=CPU_OUT_OF_SPEC
    [    9.230901] Hardware name: Qualcomm Technologies, Inc. SM8650 HDK (DT)
    [    9.230901] pstate: 01400005 (nzcv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
    [    9.230903] pc : qce_ahash_update+0x4/0x1f4
    [    9.230910] lr : ahash_do_req_chain+0xb4/0x19c
    [    9.230915] sp : ffff800084928030
    [    9.230915] x29: ffff8000849281a0 x28: 0000000000000003 x27: 0000000000000001
    [    9.230918] x26: ffff0008022d8060 x25: ffff000800a33500 x24: ffff80008492b8d8
    [    9.230920] x23: ffff80008492b918 x22: 0000000000000400 x21: ffff000800a33510
    [    9.230922] x20: ffff000800b62030 x19: ffff00080122d400 x18: 00000000ffffffff
    [    9.230923] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000
    [    9.230925] x14: 0000000000000001 x13: 0000000000000000 x12: 0000000000000000
    [    9.230927] x11: eee1c132902c61e2 x10: 0000000000000063 x9 : 0000000000000000
    [    9.230928] x8 : 0000000000000062 x7 : a54ff53a3c6ef372 x6 : 0000000000000400
    [    9.230930] x5 : fefefefefefefefe x4 : ffff000800a33510 x3 : 0000000000000000
    [    9.230931] x2 : ffff000805d76900 x1 : ffffcea2349738cc x0 : ffff00080122d400
    [    9.230933] Kernel panic - not syncing: kernel stack overflow
    [    9.230934] CPU: 6 UID: 0 PID: 747 Comm: cryptomgr_test Tainted: G S                  6.16.0-rc1-00237-g84ffcd88616f #7 PREEMPT 
    [    9.230936] Tainted: [S]=CPU_OUT_OF_SPEC
    [    9.230937] Hardware name: Qualcomm Technologies, Inc. SM8650 HDK (DT)
    [    9.230938] Call trace:
    [    9.230939]  show_stack+0x18/0x24 (C)
    [    9.230943]  dump_stack_lvl+0x60/0x80
    [    9.230947]  dump_stack+0x18/0x24
    [    9.230949]  panic+0x168/0x360
    [    9.230952]  add_taint+0x0/0xbc
    [    9.230955]  panic_bad_stack+0x108/0x120
    [    9.230958]  handle_bad_stack+0x34/0x40
    [    9.230962]  __bad_stack+0x80/0x84
    [    9.230963]  qce_ahash_update+0x4/0x1f4 (P)
    [    9.230965]  crypto_ahash_update+0x17c/0x18c
    [    9.230967]  crypto_ahash_finup+0x184/0x1e4
    [    9.230969]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230970]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230972]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230973]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230974]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230976]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230977]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230979]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230980]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230981]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230983]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230984]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230986]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230988]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230989]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230991]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230993]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230995]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230996]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230998]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.230999]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.231001]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.231002]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.231004]  crypto_ahash_finup+0x1ac/0x1e4
    [    9.231005]  crypto_ahash_finup+0x1ac/0x1e4

    [the above line repeated a few hundred times more...]

    [    9.231571]  test_ahash_vec_cfg+0x508/0x8f8
    [    9.231573]  test_hash_vec+0xb8/0x21c
    [    9.231575]  __alg_test_hash+0x144/0x2e0
    [    9.231577]  alg_test_hash+0xc0/0x178
    [    9.231578]  alg_test+0x148/0x5ec
    [    9.231579]  cryptomgr_test+0x24/0x40
    [    9.231581]  kthread+0x12c/0x204
    [    9.231583]  ret_from_fork+0x10/0x20
    [    9.231587] SMP: stopping secondary CPUs
    [    9.240072] Kernel Offset: 0x4ea1b2a80000 from 0xffff800080000000
    [    9.240073] PHYS_OFFSET: 0xfff1000080000000
    [    9.240074] CPU features: 0x6000,000001c0,62130cb1,357e7667
    [    9.240075] Memory Limit: none
    [   11.373410] ---[ end Kernel panic - not syncing: kernel stack overflow ]---

After disabling the crypto self-tests, I was then able to run a benchmark of
SHA-256 hashing 4096-byte messages, which fortunately didn't encounter the
recursion bug.  I got the following results:

    ARMv8 crypto extensions: 1864 MB/s
    Generic C code: 358 MB/s
    Qualcomm Crypto Engine: 55 MB/s

So just to clarify, you believe that asynchronous hash drivers like the Qualcomm
Crypto Engine one are useful, and the changes that you're requiring to the
CPU-based code are to support these drivers?

- Eric