From: Nick Desaulniers ndesaulniers@google.com
mainline inclusion from mainline-v5.13-rc1 commit 2515dd6ce8e545b0b2eece84920048ef9ed846c4 category: featrue bugzilla: https://gitee.com/openeuler/kernel/issues/I5YQ6Z CVE: NA
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?i...
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"o" isn't a common asm() constraint to use; it triggers an assertion in assert-enabled builds of LLVM that it's not recognized when targeting aarch64 (though it appears to fall back to "m"). It's fixed in LLVM 13 now, but there isn't really a good reason to use "o" in particular here. To avoid causing build issues for those using assert-enabled builds of earlier LLVM versions, the constraint needs changing.
Instead, if the point is to retain the __builtin_alloca(), make ptr appear to "escape" via being an input to an empty inline asm block. This is preferable anyways, since otherwise this looks like a dead store.
While the use of "r" was considered in
https://lore.kernel.org/lkml/202104011447.2E7F543@keescook/
it was only tested as an output (which looks like a dead store, and wasn't sufficient).
Use "r" as an input constraint instead, which behaves correctly across compilers and architectures.
Fixes: 39218ff4c625 ("stack: Optionally randomize kernel stack offset each syscall") Signed-off-by: Nick Desaulniers ndesaulniers@google.com Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Kees Cook keescook@chromium.org Tested-by: Nathan Chancellor nathan@kernel.org Reviewed-by: Nathan Chancellor nathan@kernel.org Link: https://reviews.llvm.org/D100412 Link: https://bugs.llvm.org/show_bug.cgi?id=49956 Link: https://lore.kernel.org/r/20210419231741.4084415-1-keescook@chromium.org Signed-off-by: Yi Yang yiyang13@huawei.com Reviewed-by: Xiu Jianfeng xiujianfeng@huawei.com Signed-off-by: Zheng Zengkai zhengzengkai@huawei.com --- include/linux/randomize_kstack.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/randomize_kstack.h b/include/linux/randomize_kstack.h index fd80fab663a9..bebc911161b6 100644 --- a/include/linux/randomize_kstack.h +++ b/include/linux/randomize_kstack.h @@ -38,7 +38,7 @@ void *__builtin_alloca(size_t size); u32 offset = raw_cpu_read(kstack_offset); \ u8 *ptr = __builtin_alloca(KSTACK_OFFSET_MAX(offset)); \ /* Keep allocation even after "ptr" loses scope. */ \ - asm volatile("" : "=o"(*ptr) :: "memory"); \ + asm volatile("" :: "r"(ptr) : "memory"); \ } \ } while (0)