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Date: Sat, 8 Jan 2022 10:31:13 +0100 From: Ard Biesheuvel <ardb@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>, Catalin Marinas <catalin.marinas@....com>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, linux-hardening@...r.kernel.org Subject: Re: [PATCH] arm64: atomics: Dereference matching size On Sat, 8 Jan 2022 at 00:28, Kees Cook <keescook@...omium.org> wrote: > > When building with -Warray-bounds (which is desired to be enabled > globally), the following warning is generated: > > In file included from ./arch/arm64/include/asm/lse.h:16, > from ./arch/arm64/include/asm/cmpxchg.h:14, > from ./arch/arm64/include/asm/atomic.h:16, > from ./include/linux/atomic.h:7, > from ./include/asm-generic/bitops/atomic.h:5, > from ./arch/arm64/include/asm/bitops.h:25, > from ./include/linux/bitops.h:33, > from ./include/linux/kernel.h:22, > from kernel/printk/printk.c:22: > ./arch/arm64/include/asm/atomic_lse.h:247:9: warning: array subscript 'long unsigned int[0]' is partly outside array bounds of 'atomic_t[1]' [-Warray-bounds] > 247 | asm volatile( \ > | ^~~ > ./arch/arm64/include/asm/atomic_lse.h:266:1: note: in expansion of macro '__CMPXCHG_CASE' > 266 | __CMPXCHG_CASE(w, , acq_, 32, a, "memory") > | ^~~~~~~~~~~~~~ > kernel/printk/printk.c:3606:17: note: while referencing 'printk_cpulock_owner' > 3606 | static atomic_t printk_cpulock_owner = ATOMIC_INIT(-1); > | ^~~~~~~~~~~~~~~~~~~~ > > This is due to the compiler seeing an unsigned long * cast against > something (atomic_t) that is int sized. Replace the cast with the > matching size cast. This results in no change in binary output. > > Cc: Will Deacon <will@...nel.org> > Cc: Peter Zijlstra <peterz@...radead.org> > Cc: Boqun Feng <boqun.feng@...il.com> > Cc: Catalin Marinas <catalin.marinas@....com> > Cc: linux-arm-kernel@...ts.infradead.org > Signed-off-by: Kees Cook <keescook@...omium.org> Acked-by: Ard Biesheuvel <ardb@...nel.org> > --- > arch/arm64/include/asm/atomic_lse.h | 2 +- > arch/arm64/include/asm/cmpxchg.h | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h > index d955ade5df7c..5d460f6b7675 100644 > --- a/arch/arm64/include/asm/atomic_lse.h > +++ b/arch/arm64/include/asm/atomic_lse.h > @@ -249,7 +249,7 @@ __lse__cmpxchg_case_##name##sz(volatile void *ptr, \ > " mov %" #w "[tmp], %" #w "[old]\n" \ > " cas" #mb #sfx "\t%" #w "[tmp], %" #w "[new], %[v]\n" \ > " mov %" #w "[ret], %" #w "[tmp]" \ > - : [ret] "+r" (x0), [v] "+Q" (*(unsigned long *)ptr), \ > + : [ret] "+r" (x0), [v] "+Q" (*(u##sz *)ptr), \ > [tmp] "=&r" (tmp) \ > : [old] "r" (x1), [new] "r" (x2) \ > : cl); \ > diff --git a/arch/arm64/include/asm/cmpxchg.h b/arch/arm64/include/asm/cmpxchg.h > index f9bef42c1411..497acf134d99 100644 > --- a/arch/arm64/include/asm/cmpxchg.h > +++ b/arch/arm64/include/asm/cmpxchg.h > @@ -243,7 +243,7 @@ static inline void __cmpwait_case_##sz(volatile void *ptr, \ > " cbnz %" #w "[tmp], 1f\n" \ > " wfe\n" \ > "1:" \ > - : [tmp] "=&r" (tmp), [v] "+Q" (*(unsigned long *)ptr) \ > + : [tmp] "=&r" (tmp), [v] "+Q" (*(u##sz *)ptr) \ > : [val] "r" (val)); \ > } > > -- > 2.30.2 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@...ts.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
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