linux-kernel - RE: [PATCH v4 10/24] crypto: x86/poly

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Date:   Mon, 28 Nov 2022 18:48:50 +0000
From:   "Elliott, Robert (Servers)" <elliott@....com>
To:     Herbert Xu <herbert@...dor.apana.org.au>,
        Ard Biesheuvel <ardb@...nel.org>
CC:     "Jason A. Donenfeld" <Jason@...c4.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "tim.c.chen@...ux.intel.com" <tim.c.chen@...ux.intel.com>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "David.Laight@...lab.com" <David.Laight@...lab.com>,
        "ebiggers@...nel.org" <ebiggers@...nel.org>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v4 10/24] crypto: x86/poly - limit FPU preemption



> On Fri, Nov 25, 2022 at 09:59:17AM +0100, Ard Biesheuvel wrote:
> > Note that it is only used in shash implementations, given that they
> > are the only ones that may receive unbounded inputs.
> 
> Although typical usage probably doesn't stress this, the length of the
> additional associated data presented to aead implementations is
> unconstrained as well. At least in x86, they can end up processing
> multiple megabytes in one chunk like the hash functions (if the
> associated data is a big buffer described by a sg list created
> with sg_init_one()).
> 

Reviewing the two arm64 aead drivers, aes-ce-ccm-glue.c solves that by
including this in the do/while loop in ccm_calculate_auth_mac():
                n = min_t(u32, n, SZ_4K); /* yield NEON at least every 4k */

That was added by 36a916af641 ("crypto: arm64/aes-ccm - yield NEON
when processing auth-only data") in 2021, also relying on
41691c44606b ("crypto: arm64/aes-ccm - reduce NEON begin/end calls
for common case").

ghash-ce-glue.c seems to be missing that in its similar function named
gcm_calculate_auth_mac().