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From:   "Elliott, Robert (Servers)" <elliott@hpe.com>
To:     Herbert Xu <herbert@gondor.apana.org.au>,
        Eric Biggers <ebiggers@kernel.org>
CC:     "davem@davemloft.net" <davem@davemloft.net>,
        "Jason@zx2c4.com" <Jason@zx2c4.com>,
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        "David.Laight@aculab.com" <David.Laight@aculab.com>,
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Subject: RE: [PATCH 03/13] crypto: x86/sha - yield FPU context during long
 loops
Thread-Topic: [PATCH 03/13] crypto: x86/sha - yield FPU context during long
 loops
Thread-Index: AQHZE/XDWaAb3QEorke1SC9apjqFca6akXiAgACzCACAAIMpAIAAAGsAgAEWHVA=
Date:   Fri, 13 Jan 2023 19:35:07 +0000
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> -----Original Message-----
> From: Herbert Xu <herbert@gondor.apana.org.au>
> Sent: Thursday, January 12, 2023 8:38 PM
> To: Eric Biggers <ebiggers@kernel.org>
> Cc: Elliott, Robert (Servers) <elliott@hpe.com>; davem@davemloft.net;
> Jason@zx2c4.com; ardb@kernel.org; ap420073@gmail.com;
> David.Laight@aculab.com; tim.c.chen@linux.intel.com; peter@n8pjl.ca;
> tglx@linutronix.de; mingo@redhat.com; bp@alien8.de;
> dave.hansen@linux.intel.com; linux-crypto@vger.kernel.org; x86@kernel.org=
;
> linux-kernel@vger.kernel.org
> Subject: Re: [PATCH 03/13] crypto: x86/sha - yield FPU context during lon=
g
> loops
>=20
> On Fri, Jan 13, 2023 at 10:36:08AM +0800, Herbert Xu wrote:
> >
> > Perhaps we should just convert any users that trigger these warnings
> > over to ahash? The shash interface was never meant to process large
> > amounts of data anyway.
>=20
> We could even add some length checks in shash to ensure that
> all large updates fail with a big bright warning once the existing
> users have been converted.

The call trace that triggered this whole topic was checking module
signatures during boot (thousands of files totaling 2.4 GB):
[   29.729849]  ? sha512_finup.part.0+0x1de/0x230 [sha512_ssse3]
[   29.729851]  ? pkcs7_digest+0xaf/0x1f0
[   29.729854]  ? pkcs7_verify+0x61/0x540
[   29.729856]  ? verify_pkcs7_message_sig+0x4a/0xe0
[   29.729859]  ? pkcs7_parse_message+0x174/0x1b0
[   29.729861]  ? verify_pkcs7_signature+0x4c/0x80
[   29.729862]  ? mod_verify_sig+0x74/0x90
[   29.729867]  ? module_sig_check+0x87/0xd0
[   29.729868]  ? load_module+0x4e/0x1fc0
[   29.729871]  ? xfs_file_read_iter+0x70/0xe0 [xfs]
[   29.729955]  ? __kernel_read+0x118/0x290
[   29.729959]  ? ima_post_read_file+0xac/0xc0
[   29.729962]  ? kernel_read_file+0x211/0x2a0
[   29.729965]  ? __do_sys_finit_module+0x93/0xf0

pkcs_digest() uses shash like this:
        /* Allocate the hashing algorithm we're going to need and find out =
how
         * big the hash operational data will be.
         */
        tfm =3D crypto_alloc_shash(sinfo->sig->hash_algo, 0, 0);
        if (IS_ERR(tfm))
                return (PTR_ERR(tfm) =3D=3D -ENOENT) ? -ENOPKG : PTR_ERR(tf=
m);

        desc_size =3D crypto_shash_descsize(tfm) + sizeof(*desc);
        sig->digest_size =3D crypto_shash_digestsize(tfm);

        ret =3D -ENOMEM;
        sig->digest =3D kmalloc(sig->digest_size, GFP_KERNEL);
        if (!sig->digest)
                goto error_no_desc;

        desc =3D kzalloc(desc_size, GFP_KERNEL);
        if (!desc)
                goto error_no_desc;

        desc->tfm   =3D tfm;

        /* Digest the message [RFC2315 9.3] */
        ret =3D crypto_shash_digest(desc, pkcs7->data, pkcs7->data_len,
                                  sig->digest);
        if (ret < 0)
                goto error;
        pr_devel("MsgDigest =3D [%*ph]\n", 8, sig->digest);

There is a crypto_ahash_digest() available. Interestingly, the number of
users of each one happens to be identical:
    $ grep -Er --include '*.[chS]' "crypto_shash_digest\(" | wc -l
    37
    $ grep -Er --include '*.[chS]' "crypto_ahash_digest\(" | wc -l
    37