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 unsigned wrap-around addition test to use
check_add_overflow(), retaining the result for later usage (which removes
the redundant open-coded addition). 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: Jeremy Kerr <j...@ozlabs.org>
Cc: Joel Stanley <j...@jms.id.au>
Cc: Alistar Popple <alist...@popple.id.au>
Cc: Eddie James <eaja...@linux.ibm.com>
Cc: linux-...@lists.ozlabs.org
Signed-off-by: Kees Cook <keesc...@chromium.org>
---
drivers/fsi/fsi-core.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
index 097d5a780264..46b24d0aadc6 100644
--- a/drivers/fsi/fsi-core.c
+++ b/drivers/fsi/fsi-core.c
@@ -381,10 +381,12 @@ EXPORT_SYMBOL_GPL(fsi_slave_write);
int fsi_slave_claim_range(struct fsi_slave *slave,
uint32_t addr, uint32_t size)
{
- if (addr + size < addr)
+ uint32_t sum;
+
+ if (check_add_overflow(addr, size, &sum))
return -EINVAL;
- if (addr + size > slave->size)
+ if (sum > slave->size)
return -EINVAL;
/* todo: check for overlapping claims */
--
2.34.1
