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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Cc: David Airlie <airlied@xxxxxxxxxx> Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- drivers/char/agp/generic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c index 3ffbb1c80c5c..fc2d07654154 100644 --- a/drivers/char/agp/generic.c +++ b/drivers/char/agp/generic.c @@ -228,7 +228,7 @@ struct agp_memory *agp_allocate_memory(struct agp_bridge_data *bridge, cur_memory = atomic_read(&bridge->current_memory_agp); if ((cur_memory + page_count > bridge->max_memory_agp) || - (cur_memory + page_count < page_count)) + (add_would_overflow(page_count, cur_memory))) return NULL; if (type >= AGP_USER_TYPES) { -- 2.34.1
