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Date: Mon, 16 May 2022 17:06:30 -0700 From: Kees Cook <keescook@...omium.org> To: Peter Zijlstra <peterz@...radead.org> Cc: Kees Cook <keescook@...omium.org>, Christophe de Dinechin <dinechin@...hat.com>, Ingo Molnar <mingo@...hat.com>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com>, linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org Subject: [PATCH v2] sched/core: Address classes via __begin_sched_classes GCC 12 is very sensitive about array checking, and views all negative array accesses as unsafe (a not unreasonable position). Redefine sched_class_highest in terms of its location from __begin_sched_classes, and redefine sched_class_lowest to the actual lowest sched class instead of one lower (and adjust the for loop so it still works). Silences this warning: In file included from kernel/sched/core.c:81: kernel/sched/core.c: In function ‘set_rq_online.part.0’: kernel/sched/sched.h:2197:52: error: array subscript -1 is outside array bounds of ‘struct sched_class[44343134792571037]’ [-Werror=array-bounds] 2197 | #define sched_class_lowest (__begin_sched_classes - 1) | ^ kernel/sched/sched.h:2200:41: note: in definition of macro ‘for_class_range’ 2200 | for (class = (_from); class != (_to); class--) | ^~~ kernel/sched/sched.h:2203:53: note: in expansion of macro ‘sched_class_lowest’ 2203 |for_class_range(class, sched_class_highest, sched_class_lowest) | ^~~~~~~~~~~~~~~~~~ kernel/sched/core.c:9115:17: note: in expansion of macro ‘for_each_class’ 9115 | for_each_class(class) { | ^~~~~~~~~~~~~~ kernel/sched/sched.h:2193:27: note: at offset -208 into object ‘__begin_sched_classes’ of size [0, 9223372036854775807] 2193 | extern struct sched_class __begin_sched_classes[]; | ^~~~~~~~~~~~~~~~~~~~~ These can't just be object pointers because GCC still sees it as an address of a single struct. Reported-by: Christophe de Dinechin <dinechin@...hat.com> Link: https://lore.kernel.org/lkml/20220414150855.2407137-2-dinechin@redhat.com/ Cc: Ingo Molnar <mingo@...hat.com> Cc: Juri Lelli <juri.lelli@...hat.com> Cc: Vincent Guittot <vincent.guittot@...aro.org> Cc: Dietmar Eggemann <dietmar.eggemann@....com> Cc: Steven Rostedt <rostedt@...dmis.org> Cc: Ben Segall <bsegall@...gle.com> Cc: Mel Gorman <mgorman@...e.de> Cc: Daniel Bristot de Oliveira <bristot@...hat.com> Signed-off-by: Kees Cook <keescook@...omium.org> --- v1: https://lore.kernel.org/lkml/20220516194241.3064242-1-keescook@chromium.org v2: use the arrays with proper indexes and adjusted loop logic --- kernel/sched/sched.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 8dccb34eb190..09304c01e5ea 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -2193,11 +2193,13 @@ const struct sched_class name##_sched_class \ extern struct sched_class __begin_sched_classes[]; extern struct sched_class __end_sched_classes[]; -#define sched_class_highest (__end_sched_classes - 1) -#define sched_class_lowest (__begin_sched_classes - 1) +#define sched_class_highest (&__begin_sched_classes[__end_sched_classes \ + - __begin_sched_classes \ + - 1]) +#define sched_class_lowest (&__begin_sched_classes[0]) #define for_class_range(class, _from, _to) \ - for (class = (_from); class != (_to); class--) + for (class = (_from); class >= (_to); class--) #define for_each_class(class) \ for_class_range(class, sched_class_highest, sched_class_lowest) -- 2.32.0
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