Re: [PATCH v4 3/7] s390/crypto: Fix use of mutex in atomic context in PAES

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] The standard AES CTR implementation uses `mutex_trylock()` and `mutex_unlock()` in a context that may be atomic, which violates core kernel locking rules.
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--- Patch [3]: [PATCH v4 3/7] s390/crypto: Fix use of mutex in atomic context in PAES ---
commit d6ba4976a19245fd83ba5c797399a6bd57d986bb
Author: Harald Freudenberger <[email protected]>

s390/crypto: Fix use of mutex in atomic context in PAES

The PAES CTR implementation used a mutex to lock one page of exclusive
memory for fast CTR processing. This commit replaces the mutex with a
binary semaphore, since a mutex is not safe to use in atomic or interrupt
context.

> diff --git a/arch/s390/crypto/paes_s390.c b/arch/s390/crypto/paes_s390.c
> index d075b0241f1f5..e8bbfc376ebb1 100644
> --- a/arch/s390/crypto/paes_s390.c
> +++ b/arch/s390/crypto/paes_s390.c
[ ... ]
> @@ -45,7 +45,7 @@ module_param_named(clrkey, pkey_clrkey_allowed, bool, 0444);
>  MODULE_PARM_DESC(clrkey, "Allow clear key material (default N)");
>  
>  static u8 *ctrblk;
> -static DEFINE_MUTEX(ctrblk_lock);
> +static DEFINE_SEMAPHORE(ctrblk_sem, 1);

[Severity: High]
This is a pre-existing issue, but does the standard AES implementation in
arch/s390/crypto/aes_s390.c suffer from this exact same problem?

Looking at ctr_aes_crypt() in arch/s390/crypto/aes_s390.c:

	locked = mutex_trylock(&ctrblk_lock);

	ret = skcipher_walk_virt(&walk, req, false);
	while ((nbytes = walk.nbytes) >= AES_BLOCK_SIZE) {
	...
	}
	if (locked)
		mutex_unlock(&ctrblk_lock);

Network traffic processing (e.g., IPsec) executes SKCIPHER operations from
a softirq context. Unlocking a mutex in an interrupt context triggers a
kernel panic or BUG on PREEMPT_RT kernels, and lockdep warnings on
standard kernels.

Since this patch successfully fixes the issue for PAES, should a similar
fix be applied to arch/s390/crypto/aes_s390.c?

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Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=3