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Message-ID: <69080fb8cace486db4e28e2e90f1d550@AcuMS.aculab.com> Date: Sat, 8 Oct 2022 21:53:33 +0000 From: David Laight <David.Laight@...LAB.COM> To: "'Jason A. Donenfeld'" <Jason@...c4.com>, Kees Cook <keescook@...omium.org> CC: Christophe Leroy <christophe.leroy@...roup.eu>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "patches@...ts.linux.dev" <patches@...ts.linux.dev>, Andreas Noever <andreas.noever@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, "Andy Shevchenko" <andriy.shevchenko@...ux.intel.com>, Borislav Petkov <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>, Christoph Böhmwalder <christoph.boehmwalder@...bit.com>, Christoph Hellwig <hch@....de>, Daniel Borkmann <daniel@...earbox.net>, "Dave Airlie" <airlied@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>, "David S . Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>, Florian Westphal <fw@...len.de>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, "H . Peter Anvin" <hpa@...or.com>, "Heiko Carstens" <hca@...ux.ibm.com>, Helge Deller <deller@....de>, Herbert Xu <herbert@...dor.apana.org.au>, Huacai Chen <chenhuacai@...nel.org>, "Hugh Dickins" <hughd@...gle.com>, Jakub Kicinski <kuba@...nel.org>, "James E . J . Bottomley" <jejb@...ux.ibm.com>, Jan Kara <jack@...e.com>, Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>, Johannes Berg <johannes@...solutions.net>, Jonathan Corbet <corbet@....net>, "Jozsef Kadlecsik" <kadlec@...filter.org>, KP Singh <kpsingh@...nel.org>, Marco Elver <elver@...gle.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, "Michael Ellerman" <mpe@...erman.id.au>, Pablo Neira Ayuso <pablo@...filter.org>, "Paolo Abeni" <pabeni@...hat.com>, Peter Zijlstra <peterz@...radead.org>, "Richard Weinberger" <richard@....at>, Russell King <linux@...linux.org.uk>, "Theodore Ts'o" <tytso@....edu>, Thomas Bogendoerfer <tsbogend@...ha.franken.de>, "Thomas Gleixner" <tglx@...utronix.de>, Thomas Graf <tgraf@...g.ch>, Ulf Hansson <ulf.hansson@...aro.org>, Vignesh Raghavendra <vigneshr@...com>, WANG Xuerui <kernel@...0n.name>, Will Deacon <will@...nel.org>, Yury Norov <yury.norov@...il.com>, "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>, "kasan-dev@...glegroups.com" <kasan-dev@...glegroups.com>, "kernel-janitors@...r.kernel.org" <kernel-janitors@...r.kernel.org>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>, "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>, "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>, "linux-mm@...ck.org" <linux-mm@...ck.org>, "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>, "linux-mtd@...ts.infradead.org" <linux-mtd@...ts.infradead.org>, "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>, "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>, "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>, "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>, "linux-um@...ts.infradead.org" <linux-um@...ts.infradead.org>, "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>, "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "loongarch@...ts.linux.dev" <loongarch@...ts.linux.dev>, "netdev@...r.kernel.org" <netdev@...r.kernel.org>, "sparclinux@...r.kernel.org" <sparclinux@...r.kernel.org>, "x86@...nel.org" <x86@...nel.org>, Toke Høiland-Jørgensen <toke@...e.dk>, Chuck Lever <chuck.lever@...cle.com>, Jan Kara <jack@...e.cz> Subject: RE: [PATCH v3 3/5] treewide: use get_random_u32() when possible From: Jason A. Donenfeld > Sent: 07 October 2022 18:56 ... > > Given these kinds of less mechanical changes, it may make sense to split > > these from the "trivial" conversions in a treewide patch. The chance of > > needing a revert from the simple 1:1 conversions is much lower than the > > need to revert by-hand changes. > > > > The Cocci script I suggested in my v1 review gets 80% of the first > > patch, for example. > > I'll split things up into a mechanical step and a non-mechanical step. > Good idea. I'd also do something about the 'get_random_int() & 3' cases. (ie remainder by 2^n-1) These can be converted to 'get_random_u8() & 3' (etc). So they only need one random byte (not 4) and no multiply. Possibly something based on (the quickly typed, and not C): #define get_random_below(val) [ if (builtin_constant(val)) BUILD_BUG_ON(!val || val > 0x100000000ull) if (!(val & (val - 1)) { if (val <= 0x100) return get_random_u8() & (val - 1); if (val <= 0x10000) return get_random_u16() & (val - 1); return get_random_u32() & (val - 1); } } BUILD_BUG_ON(sizeof (val) > 4); return ((u64)get_random_u32() * val) >> 32; } get_random_below() is a much better name than prandom_u32_max(). David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
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