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: Wu Hao <hao.wu@xxxxxxxxx> Cc: Tom Rix <trix@xxxxxxxxxx> Cc: Moritz Fischer <mdf@xxxxxxxxxx> Cc: Xu Yilun <yilun.xu@xxxxxxxxx> Cc: linux-fpga@xxxxxxxxxxxxxxx Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> --- drivers/fpga/dfl.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/drivers/fpga/dfl.c b/drivers/fpga/dfl.c index e6d12fbab653..7d10780e3a98 100644 --- a/drivers/fpga/dfl.c +++ b/drivers/fpga/dfl.c @@ -1939,15 +1939,16 @@ static int do_set_irq_trigger(struct dfl_feature *feature, unsigned int idx, int dfl_fpga_set_irq_triggers(struct dfl_feature *feature, unsigned int start, unsigned int count, int32_t *fds) { + unsigned int sum; unsigned int i; int ret = 0; /* overflow */ - if (unlikely(start + count < start)) + if (unlikely(check_add_overflow(start, count, &sum))) return -EINVAL; /* exceeds nr_irqs */ - if (start + count > feature->nr_irqs) + if (sum > feature->nr_irqs) return -EINVAL; for (i = 0; i < count; i++) { -- 2.34.1
