In an effort to separate intentional arithmetic wrap-around from
unexpected wrap-around, we need to refactor places that depend on this
kind of math. One of the most common code patterns of this is:
VAR + value < VAR
Notably, this is considered "undefined behavior" for signed and pointer
types, which the kernel works around by using the -fno-strict-overflow
option in the build[1] (which used to just be -fwrapv). Regardless, we
want to get the kernel source to the position where we can meaningfully
instrument arithmetic wrap-around conditions and catch them when they
are unexpected, regardless of whether they are signed[2], unsigned[3],
or pointer[4] types.
Refactor open-coded wrap-around addition test to use add_would_overflow().
This paves the way to enabling the wrap-around sanitizers in the future.
Link: https://git.kernel.org/linus/68df3755e383e6fecf2354a67b08f92f18536594 [1]
Link: https://github.com/KSPP/linux/issues/26 [2]
Link: https://github.com/KSPP/linux/issues/27 [3]
Link: https://github.com/KSPP/linux/issues/344 [4]
Cc: Yoshinori Sato <ys...@users.sourceforge.jp>
Cc: Rich Felker <dal...@libc.org>
Cc: John Paul Adrian Glaubitz <glaub...@physik.fu-berlin.de>
Cc: linux...@vger.kernel.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
arch/sh/kernel/sys_sh.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/sh/kernel/sys_sh.c b/arch/sh/kernel/sys_sh.c
index a5a7b33ed81a..e390caeb8c00 100644
--- a/arch/sh/kernel/sys_sh.c
+++ b/arch/sh/kernel/sys_sh.c
@@ -66,7 +66,7 @@ asmlinkage int sys_cacheflush(unsigned long addr, unsigned
long len, int op)
* Verify that the specified address region actually belongs
* to this process.
*/
- if (addr + len < addr)
+ if (add_would_overflow(addr, len))
return -EFAULT;
mmap_read_lock(current->mm);
--
2.34.1
