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: Karol Herbst <[email protected]>
Cc: Lyude Paul <[email protected]>
Cc: Danilo Krummrich <[email protected]>
Cc: David Airlie <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Ben Skeggs <[email protected]>
Cc: Dave Airlie <[email protected]>
Cc: Julia Lawall <[email protected]>
Cc: Jiang Jian <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Kees Cook <[email protected]>
---
drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff --git a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
index 9c97800fe037..6ca1a82ccbc1 100644
--- a/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
+++ b/drivers/gpu/drm/nouveau/nvkm/subdev/mmu/vmm.c
@@ -1149,13 +1149,15 @@ nvkm_vmm_ctor(const struct nvkm_vmm_func *func, struct
nvkm_mmu *mmu,
vmm->root = RB_ROOT;
if (managed) {
+ u64 sum;
+
/* Address-space will be managed by the client for the most
* part, except for a specified area where NVKM allocations
* are allowed to be placed.
*/
vmm->start = 0;
vmm->limit = 1ULL << bits;
- if (addr + size < addr || addr + size > vmm->limit)
+ if (check_add_overflow(addr, size, &sum) || sum > vmm->limit)
return -EINVAL;
/* Client-managed area before the NVKM-managed area. */
@@ -1174,7 +1176,7 @@ nvkm_vmm_ctor(const struct nvkm_vmm_func *func, struct
nvkm_mmu *mmu,
}
/* Client-managed area after the NVKM-managed area. */
- addr = addr + size;
+ addr = sum;
size = vmm->limit - addr;
if (size && (ret = nvkm_vmm_ctor_managed(vmm, addr, size)))
return ret;
--
2.34.1
