Hi Jan,

Just out of curiosity, have you tried to use "76" on both values to
check if the problem still happens?

-- 
Regards,
Marcelo

On Fri, Sep 23, 2016 at 08:22:27PM -0400, Jan Stancek wrote:
> Hi,
> 
> I'm chasing a memory corruption with 4.8-rc7 as I'm observing random Oopses
> on ppc BE/LE systems (lpars, KVM guests). About 30% of issues is that
> module list gets corrupted, and "cat /proc/modules" or "lsmod" triggers
> an Oops, for example:
> 
> [   88.486041] Unable to handle kernel paging request for data at address 0x00000020
> ...
> [   88.487658] NIP [c00000000020f820] m_show+0xa0/0x240
> [   88.487689] LR [c00000000020f834] m_show+0xb4/0x240
> [   88.487719] Call Trace:
> [   88.487736] [c0000004b605bbb0] [c00000000020f834] m_show+0xb4/0x240 (unreliable)
> [   88.487796] [c0000004b605bc50] [c00000000045e73c] seq_read+0x36c/0x520
> [   88.487843] [c0000004b605bcf0] [c0000000004e1014] proc_reg_read+0x84/0x120
> [   88.487889] [c0000004b605bd30] [c00000000040df88] vfs_read+0xf8/0x380
> [   88.487934] [c0000004b605bde0] [c00000000040fd40] SyS_read+0x60/0x110
> [   88.487981] [c0000004b605be30] [c000000000009590] system_call+0x38/0xec
> 
> 0x20 offset is module_use->source, module_use is NULL because module.source_list
> gets corrupted.
> 
> The source of corruption appears to originate from a 'ahash' test for p8_ghash:
> 
> cryptomgr_test
>  alg_test
>   alg_test_hash
>    test_hash
>     __test_hash
>      ahash_partial_update
>       shash_async_export
>        memcpy
> 
> With some extra traces [1], I'm seeing that ahash_partial_update() allocates 56 bytes
> for 'state', and then crypto_ahash_export() writes 76 bytes into it:
> 
> [    5.970887] __test_hash alg name p8_ghash, result: c000000004333ac0, key: c0000004b860a500, req: c0000004b860a380
> [    5.970963] state: c000000004333f00, statesize: 56
> [    5.970995] shash_default_export memcpy c000000004333f00 c0000004b860a3e0, len: 76
> 
> This seems to directly correspond with:
>   p8_ghash_alg.descsize = sizeof(struct p8_ghash_desc_ctx) == 56
>   shash_tfm->descsize = sizeof(struct p8_ghash_desc_ctx) + crypto_shash_descsize(fallback) == 56 + 20
> where 20 is presumably coming from "ghash_alg.descsize".
> 
> My gut feeling was that these 2 should match, but I'd love to hear
> what crypto people think.
> 
> Thank you,
> Jan
> 
> [1]
> diff --git a/crypto/shash.c b/crypto/shash.c
> index a051541..49fe182 100644
> --- a/crypto/shash.c
> +++ b/crypto/shash.c
> @@ -188,6 +188,8 @@ EXPORT_SYMBOL_GPL(crypto_shash_digest);
> 
>  static int shash_default_export(struct shash_desc *desc, void *out)
>  {
> +       int len = crypto_shash_descsize(desc->tfm);
> +       printk("shash_default_export memcpy %p %p, len: %d\n", out, shash_desc_ctx(desc), len);
>         memcpy(out, shash_desc_ctx(desc), crypto_shash_descsize(desc->tfm));
>         return 0;
>  }
> diff --git a/crypto/testmgr.c b/crypto/testmgr.c
> index 5c9d5a5..2e54579 100644
> --- a/crypto/testmgr.c
> +++ b/crypto/testmgr.c
> @@ -218,6 +218,8 @@ static int ahash_partial_update(struct ahash_request **preq,
>                 pr_err("alt: hash: Failed to alloc state for %s\n", algo);
>                 goto out_nostate;
>         }
> +       printk("state: %p, statesize: %d\n", state, statesize);
> +
>         ret = crypto_ahash_export(req, state);
>         if (ret) {
>                 pr_err("alt: hash: Failed to export() for %s\n", algo);
> @@ -288,6 +290,7 @@ static int __test_hash(struct crypto_ahash *tfm, struct hash_testvec *template,
>                        "%s\n", algo);
>                 goto out_noreq;
>         }
> +       printk("__test_hash alg name %s, result: %p, key: %p, req: %p\n", algo, result, key, req);
>         ahash_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
>                                    tcrypt_complete, &tresult);
> --
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