[PATCH 74/82] ARC: dw2 unwind: Refactor intentional wrap-around test

[Kees Cook]

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: Vineet Gupta <vgupta@xxxxxxxxxx>
Cc: Luis Chamberlain <mcgrof@xxxxxxxxxx>
Cc: "dean.yang_cp" <yangdianqing@xxxxxxxxxx>
Cc: Song Liu <song@xxxxxxxxxx>
Cc: Yihao Han <hanyihao@xxxxxxxx>
Cc: linux-snps-arc@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 arch/arc/kernel/unwind.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arc/kernel/unwind.c b/arch/arc/kernel/unwind.c
index 8924fa2a8f29..649b56204580 100644
--- a/arch/arc/kernel/unwind.c
+++ b/arch/arc/kernel/unwind.c
@@ -1278,7 +1278,7 @@ int arc_unwind(struct unwind_frame_info *frame)
 			if ((state.regs[i].value * state.dataAlign)
 			    % sizeof(unsigned long)
 			    || addr < startLoc
-			    || addr + sizeof(unsigned long) < addr
+			    || add_would_overflow(addr, sizeof(unsigned long))
 			    || addr + sizeof(unsigned long) > endLoc)
 					return -EIO;
 
-- 
2.34.1