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[220.235.49.94]) by smtp.gmail.com with ESMTPSA id i135sm2496266pgd.41.2019.03.21.19.13.59 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 21 Mar 2019 19:13:59 -0700 (PDT) From: Daniel Axtens To: George Spelvin , linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH] arch/powerpc/crypto/crc-vpmsum_test: Use cheaper random numbers for self-test In-Reply-To: <201903211042.x2LAgMp3003053@sdf.org> References: <201903211042.x2LAgMp3003053@sdf.org> Date: Fri, 22 Mar 2019 13:13:56 +1100 Message-ID: <87tvfvsljv.fsf@dja-thinkpad.axtens.net> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: George Spelvin , Paul Mackerras , Herbert Xu Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi George, > This code was filling a 64K buffer from /dev/urandom in order to > compute a CRC over (on average half of) it by two different methods, > comparing the CRCs, and repeating. > > This is not a remotely security-critical application, so use the far > faster and cheaper prandom_u32() generator. > I've had a quick look at the prandom_u32 generator and I agree that it's suitable for this. > And, while we're at it, only fill as much of the buffer as we plan to use. This also looks good to me. Acked-by: Daniel Axtens Regards, Daniel > > Signed-off-by: George Spelvin > Cc: Daniel Axtens > Cc: Herbert Xu > Cc: linuxppc-dev@lists.ozlabs.org > Cc: Benjamin Herrenschmidt > Cc: Paul Mackerras > Cc: Michael Ellerman > --- > arch/powerpc/crypto/crc-vpmsum_test.c | 10 +++------- > 1 file changed, 3 insertions(+), 7 deletions(-) > > diff --git a/arch/powerpc/crypto/crc-vpmsum_test.c b/arch/powerpc/crypto/crc-vpmsum_test.c > index 0153a9c6f4af..98ea4f4d3dde 100644 > --- a/arch/powerpc/crypto/crc-vpmsum_test.c > +++ b/arch/powerpc/crypto/crc-vpmsum_test.c > @@ -78,16 +78,12 @@ static int __init crc_test_init(void) > > pr_info("crc-vpmsum_test begins, %lu iterations\n", iterations); > for (i=0; i - size_t len, offset; > + size_t offset = prandom_u32_max(16); > + size_t len = prandom_u32_max(MAX_CRC_LENGTH); > > - get_random_bytes(data, MAX_CRC_LENGTH); > - get_random_bytes(&len, sizeof(len)); > - get_random_bytes(&offset, sizeof(offset)); > - > - len %= MAX_CRC_LENGTH; > - offset &= 15; > if (len <= offset) > continue; > + prandom_bytes(data, len); > len -= offset; > > crypto_shash_update(crct10dif_shash, data+offset, len); > -- > 2.20.1