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Message-ID: <202505200914.086A9D4@keescook> Date: Tue, 20 May 2025 09:15:40 -0700 From: Kees Cook <kees@...nel.org> To: Mickaël Salaün <mic@...ikod.net> Cc: Randy Dunlap <rdunlap@...radead.org>, Steven Rostedt <rostedt@...dmis.org>, Stephen Rothwell <sfr@...b.auug.org.au>, Linux Next Mailing List <linux-next@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-security-module@...r.kernel.org, Günther Noack <gnoack@...gle.com> Subject: Re: linux-next: Tree for May 16 (security/landlock/ruleset.c) On Tue, May 20, 2025 at 04:45:19PM +0200, Mickaël Salaün wrote: > On Mon, May 19, 2025 at 12:15:30PM -0700, Kees Cook wrote: > > On Mon, May 19, 2025 at 08:41:17PM +0200, Mickaël Salaün wrote: > > > On Mon, May 19, 2025 at 11:19:53AM -0700, Kees Cook wrote: > > > > On Mon, May 19, 2025 at 05:29:30PM +0200, Mickaël Salaün wrote: > > > > > On Fri, May 16, 2025 at 07:54:14PM -0700, Randy Dunlap wrote: > > > > > > > > > > > > > > > > > > On 5/16/25 3:24 AM, Stephen Rothwell wrote: > > > > > > > Hi all, > > > > > > > > > > > > > > Changes since 20250515: > > > > > > > > > > Thanks for the report. > > > > > > > > > > It is the same warning as reported here: > > > > > https://lore.kernel.org/all/202501040747.S3LYfvYq-lkp@intel.com/ > > > > > > > > > > I don't know what the actual issue is though. > > > > > > > > > > > > > > > > > on i386: > > > > > > > > > > > > In file included from ../arch/x86/include/asm/string.h:3, > > > > > > from ../include/linux/string.h:65, > > > > > > from ../include/linux/bitmap.h:13, > > > > > > from ../include/linux/cpumask.h:12, > > > > > > from ../include/linux/smp.h:13, > > > > > > from ../include/linux/lockdep.h:14, > > > > > > from ../security/landlock/ruleset.c:16: > > > > > > ../security/landlock/ruleset.c: In function 'create_rule': > > > > > > ../arch/x86/include/asm/string_32.h:150:25: warning: '__builtin_memcpy' accessing 4294967295 bytes at offsets 20 and 0 overlaps 6442450943 bytes at offset -2147483648 [-Wrestrict] > > > > > > 150 | #define memcpy(t, f, n) __builtin_memcpy(t, f, n) > > > > > > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > > > > > > ../security/landlock/ruleset.c:137:9: note: in expansion of macro 'memcpy' > > > > > > 137 | memcpy(new_rule->layers, layers, > > > > > > | ^~~~~~ > > > > > > > > > > > > > > > > > > Full randconfig file is attached. > > > > > > > > The trigger appears to be CONFIG_PROFILE_ALL_BRANCHES, and GCC getting > > > > tricked into thinking check_mul_overflow() returns true: > > > > > > > > In file included from ../arch/x86/include/asm/string.h:3, > > > > from ../include/linux/string.h:65, > > > > from ../include/linux/bitmap.h:13, > > > > from ../include/linux/cpumask.h:12, > > > > from ../include/linux/smp.h:13, > > > > from ../include/linux/lockdep.h:14, > > > > from ../security/landlock/ruleset.c:16: > > > > ../security/landlock/ruleset.c: In function 'create_rule': > > > > ../arch/x86/include/asm/string_32.h:150:25: warning: '__builtin_memcpy' accessing 4294967295 bytes at offsets 0 and 0 overlaps 6442450943 bytes at offset -2147483648 [-Wrestrict] > > > > 150 | #define memcpy(t, f, n) __builtin_memcpy(t, f, n) > > > > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ../security/landlock/ruleset.c:137:9: note: in expansion of macro 'memcpy' > > > > 137 | memcpy(new_rule->layers, layers, > > > > | ^~~~~~ > > > > 'create_rule': event 1 > > > > ../include/linux/compiler.h:69:46: > > > > 68 | (cond) ? \ > > > > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > 69 | (__if_trace.miss_hit[1]++,1) : \ > > > > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~ > > > > | | > > > > | (1) when the condition is evaluated to true > > > > 70 | (__if_trace.miss_hit[0]++,0); \ > > > > | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > ../include/linux/compiler.h:57:69: note: in expansion of macro '__trace_if_value' > > > > 57 | #define __trace_if_var(cond) (__builtin_constant_p(cond) ? (cond) : __trace_if_value(cond)) > > > > | ^~~~~~~~~~~~~~~~ > > > > ../include/linux/compiler.h:55:28: note: in expansion of macro '__trace_if_var' > > > > 55 | #define if(cond, ...) if ( __trace_if_var( !!(cond , ## __VA_ARGS__) ) ) > > > > | ^~~~~~~~~~~~~~ > > > > ../include/linux/overflow.h:270:9: note: in expansion of macro 'if' > > > > 270 | if (check_mul_overflow(factor1, factor2, &bytes)) > > > > | ^~ > > > > 'create_rule': event 2 > > > > ../arch/x86/include/asm/string_32.h:150:25: > > > > 150 | #define memcpy(t, f, n) __builtin_memcpy(t, f, n) > > > > | ^~~~~~~~~~~~~~~~~~~~~~~~~ > > > > | | > > > > | (2) out of array bounds here > > > > ../security/landlock/ruleset.c:137:9: note: in expansion of macro 'memcpy' > > > > 137 | memcpy(new_rule->layers, layers, > > > > | ^~~~~~ > > > > make[1]: Leaving directory '/srv/code/gcc-bug' > > > > > > That's interesting... > > > > > > > > > > > > > > > I'll take a look at ways to make either the overflow macros or memcpy > > > > robust against this kind of weirdness... > > > > > > Thanks! > > > > I'm doing some build testing, but the below patch makes GCC happy. > > Alternatively we could make CONFIG_PROFILE_ALL_BRANCHES=y depend on > > CONFIG_FORTIFY_SOURCE=y ... > > > > > > From 6fbf66fdfd0a7dac809b77faafdd72c60112bb8d Mon Sep 17 00:00:00 2001 > > From: Kees Cook <kees@...nel.org> > > Date: Mon, 19 May 2025 11:52:06 -0700 > > Subject: [PATCH] string.h: Provide basic sanity checks for fallback memcpy() > > MIME-Version: 1.0 > > Content-Type: text/plain; charset=UTF-8 > > Content-Transfer-Encoding: 8bit > > > > Instead of defining memcpy() in terms of __builtin_memcpy() deep > > in arch/x86/include/asm/string_32.h, notice that it is needed up in > > the general string.h, as done with other common C String APIs. This > > allows us to add basic sanity checking for pathological "size" > > arguments to memcpy(). Besides the run-time checking benefit, this > > avoids GCC trying to be very smart about value range tracking[1] when > > CONFIG_PROFILE_ALL_BRANCHES=y but FORTIFY_SOURCE=n. > > It works for me but I couldn't reproduce the issue. I tried with > CONFIG_PROFILE_ALL_BRANCHES=y and CONFIG_FORTIFY_SOURCE=n but it always > works without a warning. I'm using GCC 15. Is it specific to a version > of GCC? It must be more than just those options -- I reproduced it with Randy's randconfig under GCC 15. -- Kees Cook
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