6.14-stable review patch. If anyone has any objections, please let me know.
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From: Jann Horn jannh@google.com
[ Upstream commit 47a60391ae0ed04ffbb9bd8dcd94ad9d08b41288 ]
When arm64 is built with LTO, it upgrades READ_ONCE() to ldar / ldapr (load-acquire) to avoid issues that can be caused by the compiler optimizing away implicit address dependencies.
Unlike plain loads, these load-acquire instructions actually require an aligned address.
For now, fix it by removing the READ_ONCE() that the buggy commit introduced.
Fixes: ece69af2ede1 ("rwonce: handle KCSAN like KASAN in read_word_at_a_time()") Reported-by: Nathan Chancellor nathan@kernel.org Closes: https://lore.kernel.org/r/20250326203926.GA10484@ax162 Signed-off-by: Jann Horn jannh@google.com Signed-off-by: Arnd Bergmann arnd@arndb.de Signed-off-by: Sasha Levin sashal@kernel.org --- include/asm-generic/rwonce.h | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/include/asm-generic/rwonce.h b/include/asm-generic/rwonce.h index e9f2b84d2338c..52b969c7cef93 100644 --- a/include/asm-generic/rwonce.h +++ b/include/asm-generic/rwonce.h @@ -86,7 +86,12 @@ unsigned long read_word_at_a_time(const void *addr) kasan_check_read(addr, 1); kcsan_check_read(addr, 1);
- return READ_ONCE(*(unsigned long *)addr); + /* + * This load can race with concurrent stores to out-of-bounds memory, + * but READ_ONCE() can't be used because it requires higher alignment + * than plain loads in arm64 builds with LTO. + */ + return *(unsigned long *)addr; }
#endif /* __ASSEMBLY__ */