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Date: Wed, 12 Jan 2022 12:22:59 -0800
From: Kees Cook <keescook@...omium.org>
To: Will Deacon <will@...nel.org>
Cc: Kees Cook <keescook@...omium.org>,
Peter Zijlstra <peterz@...radead.org>,
Boqun Feng <boqun.feng@...il.com>,
Catalin Marinas <catalin.marinas@....com>,
linux-arm-kernel@...ts.infradead.org,
Ard Biesheuvel <ardb@...nel.org>,
Mark Rutland <mark.rutland@....com>,
linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: [PATCH v2] arm64: atomics: lse: Dereference matching size
When building with -Warray-bounds, 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.
Note that __ll_sc__cmpxchg_case_##name##sz already uses the same
constraint:
[v] "+Q" (*(u##sz *)ptr
Which is why only the LSE form needs updating and not the
LL/SC form, so this change is unlikely to be problematic.
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
Acked-by: Ard Biesheuvel <ardb@...nel.org>
Acked-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Kees Cook <keescook@...omium.org>
---
v1: https://lore.kernel.org/linux-hardening/20220107232746.1540130-1-keescook@chromium.org/
v2:
- add Acks
- note the existing LL/SC form
---
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
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