lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Fri, 7 Oct 2022 20:21:28 -0600 From: "Jason A. Donenfeld" <Jason@...c4.com> To: Kees Cook <keescook@...omium.org> Cc: linux-kernel@...r.kernel.org, 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>, Christophe Leroy <christophe.leroy@...roup.eu>, 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, kasan-dev@...glegroups.com, kernel-janitors@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-block@...r.kernel.org, linux-crypto@...r.kernel.org, linux-doc@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-media@...r.kernel.org, linux-mips@...r.kernel.org, linux-mm@...ck.org, linux-mmc@...r.kernel.org, linux-mtd@...ts.infradead.org, linux-nvme@...ts.infradead.org, linux-parisc@...r.kernel.org, linux-rdma@...r.kernel.org, linux-s390@...r.kernel.org, linux-um@...ts.infradead.org, linux-usb@...r.kernel.org, linux-wireless@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, loongarch@...ts.linux.dev, netdev@...r.kernel.org, sparclinux@...r.kernel.org, x86@...nel.org, Jan Kara <jack@...e.cz> Subject: Re: [PATCH v4 2/6] treewide: use prandom_u32_max() when possible On Fri, Oct 07, 2022 at 03:47:44PM -0700, Kees Cook wrote: > On Fri, Oct 07, 2022 at 12:01:03PM -0600, Jason A. Donenfeld wrote: > > Rather than incurring a division or requesting too many random bytes for > > the given range, use the prandom_u32_max() function, which only takes > > the minimum required bytes from the RNG and avoids divisions. > > I actually meant splitting the by-hand stuff by subsystem, but nearly > all of these can be done mechanically too, so it shouldn't be bad. Notes > below... Oh, cool, more coccinelle. You're basically giving me a class on these recipes. Much appreciated. > > [...] > > diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c > > index 92bcc1768f0b..87203429f802 100644 > > --- a/arch/arm64/kernel/process.c > > +++ b/arch/arm64/kernel/process.c > > @@ -595,7 +595,7 @@ unsigned long __get_wchan(struct task_struct *p) > > unsigned long arch_align_stack(unsigned long sp) > > { > > if (!(current->personality & ADDR_NO_RANDOMIZE) && randomize_va_space) > > - sp -= get_random_int() & ~PAGE_MASK; > > + sp -= prandom_u32_max(PAGE_SIZE); > > return sp & ~0xf; > > } > > > > @mask@ > expression MASK; > @@ > > - (get_random_int() & ~(MASK)) > + prandom_u32_max(MASK) Not quite! PAGE_MASK != PAGE_SIZE. In this case, things get a litttttle more complicated where you can do: get_random_int() & MASK == prandom_u32_max(MASK + 1) *only if all the top bits of MASK are set* That is, if MASK one less than a power of two. Or if MASK & (MASK + 1) == 0. (If those top bits aren't set, you can technically do prandom_u32_max(MASK >> n + 1) << n. That'd be a nice thing to work out. But yeesh, maybe a bit much for the time being and probably a bit beyond coccinelle.) This case here, though, is a bit more special, where we can just rely on an obvious given kernel identity. Namely, PAGE_MASK == ~(PAGE_SIZE - 1). So ~PAGE_MASK == PAGE_SIZE - 1. So get_random_int() & ~PAGE_MASK == prandom_u32_max(PAGE_SIZE - 1 + 1). So get_random_int() & ~PAGE_MASK == prandom_u32_max(PAGE_SIZE). And most importantly, this makes the code more readable, since everybody knows what bounding by PAGE_SIZE means, where as what on earth is happening with the &~PAGE_MASK thing. So it's a good change. I'll try to teach coccinelle about that special case. > > diff --git a/arch/loongarch/kernel/vdso.c b/arch/loongarch/kernel/vdso.c > > index f32c38abd791..8c9826062652 100644 > > --- a/arch/loongarch/kernel/vdso.c > > +++ b/arch/loongarch/kernel/vdso.c > > @@ -78,7 +78,7 @@ static unsigned long vdso_base(void) > > unsigned long base = STACK_TOP; > > > > if (current->flags & PF_RANDOMIZE) { > > - base += get_random_int() & (VDSO_RANDOMIZE_SIZE - 1); > > + base += prandom_u32_max(VDSO_RANDOMIZE_SIZE); > > base = PAGE_ALIGN(base); > > } > > > > @minus_one@ > expression FULL; > @@ > > - (get_random_int() & ((FULL) - 1) > + prandom_u32_max(FULL) Ahh, well, okay, this is the example I mentioned above. Only works if FULL is saturated. Any clever way to get coccinelle to prove that? Can it look at the value of constants? > > > diff --git a/arch/parisc/kernel/vdso.c b/arch/parisc/kernel/vdso.c > > index 63dc44c4c246..47e5960a2f96 100644 > > --- a/arch/parisc/kernel/vdso.c > > +++ b/arch/parisc/kernel/vdso.c > > @@ -75,7 +75,7 @@ int arch_setup_additional_pages(struct linux_binprm *bprm, > > > > map_base = mm->mmap_base; > > if (current->flags & PF_RANDOMIZE) > > - map_base -= (get_random_int() & 0x1f) * PAGE_SIZE; > > + map_base -= prandom_u32_max(0x20) * PAGE_SIZE; > > > > vdso_text_start = get_unmapped_area(NULL, map_base, vdso_text_len, 0, 0); > > > > These are more fun, but Coccinelle can still do them with a little > Pythonic help: > > // Find a potential literal > @literal_mask@ > expression LITERAL; > identifier randfunc =~ "get_random_int|prandom_u32|get_random_u32"; > position p; > @@ > > (randfunc()@p & (LITERAL)) > > // Add one to the literal. > @script:python add_one@ > literal << literal_mask.LITERAL; > RESULT; > @@ > > if literal.startswith('0x'): > value = int(literal, 16) + 1 > coccinelle.RESULT = cocci.make_expr("0x%x" % (value)) > elif literal[0] in '123456789': > value = int(literal, 10) + 1 > coccinelle.RESULT = cocci.make_expr("%d" % (value)) > else: > print("I don't know how to handle: %s" % (literal)) > > // Replace the literal mask with the calculated result. > @plus_one@ > expression literal_mask.LITERAL; > position literal_mask.p; > expression add_one.RESULT; > identifier FUNC; > @@ > > - (FUNC()@p & (LITERAL)) > + prandom_u32_max(RESULT) Oh that's pretty cool. I can do the saturation check in python, since `value` holds the parsed result. Neat. > > diff --git a/fs/ext2/ialloc.c b/fs/ext2/ialloc.c > > index 998dd2ac8008..f4944c4dee60 100644 > > --- a/fs/ext2/ialloc.c > > +++ b/fs/ext2/ialloc.c > > @@ -277,8 +277,7 @@ static int find_group_orlov(struct super_block *sb, struct inode *parent) > > int best_ndir = inodes_per_group; > > int best_group = -1; > > > > - group = prandom_u32(); > > - parent_group = (unsigned)group % ngroups; > > + parent_group = prandom_u32_max(ngroups); > > for (i = 0; i < ngroups; i++) { > > group = (parent_group + i) % ngroups; > > desc = ext2_get_group_desc (sb, group, NULL); > > Okay, that one is too much for me -- checking that group is never used > after the assignment removal is likely possible, but beyond my cocci > know-how. :) Yea this is a tricky one, which I initially didn't do by hand, but Jan seemed fine with it, and it's clear if you look at it. Trixy cocci indeed. > > diff --git a/lib/test_hexdump.c b/lib/test_hexdump.c > > index 0927f44cd478..41a0321f641a 100644 > > --- a/lib/test_hexdump.c > > +++ b/lib/test_hexdump.c > > @@ -208,7 +208,7 @@ static void __init test_hexdump_overflow(size_t buflen, size_t len, > > static void __init test_hexdump_overflow_set(size_t buflen, bool ascii) > > { > > unsigned int i = 0; > > - int rs = (prandom_u32_max(2) + 1) * 16; > > + int rs = prandom_u32_max(2) + 1 * 16; > > > > do { > > int gs = 1 << i; > > This looks wrong. Cocci says: > > - int rs = (get_random_int() % 2 + 1) * 16; > + int rs = (prandom_u32_max(2) + 1) * 16; !! Nice catch. Alright, I'll give this a try with more cocci. The big difficulty at the moment is the power of 2 constant checking thing. If you have any pointers on that, would be nice. Thanks a bunch for the guidance. Jason
Powered by blists - more mailing lists