Re: [PATCH 1/2] drm/msm/gem: Fix VM_BIND range check

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] drm/msm: 64-to-32-bit truncation in size_add() in vm_bind_job_lookup_ops()
--

commit 0bb1fc19abe2c004d338802c56cd54e0621aa9a6
Author: Rob Clark <robin.clark@oss.qualcomm.com>

drm/msm/gem: Fix VM_BIND range check

This commit replaces the addition of op->range and op->obj_offset with
size_add() in vm_bind_job_lookup_ops() to guard against integer overflow when
validating the range against obj->size.

> diff --git a/drivers/gpu/drm/msm/msm_gem_vma.c b/drivers/gpu/drm/msm/msm_gem_vma.c
> index f687a629629d3..16b3870d5e90e 100644
> --- a/drivers/gpu/drm/msm/msm_gem_vma.c
> +++ b/drivers/gpu/drm/msm/msm_gem_vma.c
> @@ -1118,7 +1118,7 @@ vm_bind_job_lookup_ops(struct msm_vm_bind_job *job, struct drm_msm_vm_bind *args
>  		op->obj = obj;
>  		cnt++;
>  
> -		if ((op->range + op->obj_offset) > obj->size) {
> +		if (size_add(op->range, op->obj_offset) > obj->size) {

[Severity: Medium]
On 32-bit builds, does passing op->range and op->obj_offset to size_add()
truncate the upper 32 bits of both 64-bit operands before checking for
overflow?

In struct msm_vm_bind_op, obj_offset and range are 64-bit values:

drivers/gpu/drm/msm/msm_gem_vma.c:
struct msm_vm_bind_op {
	...
	uint64_t obj_offset;
	uint64_t iova;
	uint64_t range;
	...
};

However, size_add() in include/linux/overflow.h takes size_t arguments:

static __always_inline size_t __must_check size_add(size_t addend1, size_t addend2)

Earlier in lookup_op(), op->obj_offset is only checked with
invalid_alignment(op->obj_offset), which does not reject non-zero upper 32
bits. On 32-bit architectures where size_t is 32 bits wide, an offset such as
0x100000000ULL is truncated to 0 when passed to size_add(), allowing an
out-of-bounds 64-bit op->obj_offset or op->range to bypass the obj->size
check in vm_bind_job_lookup_ops() and be stored into vma->gem.offset.

Would check_add_overflow() with a uint64_t sum (or range_overflows_t(u64,
op->obj_offset, op->range, obj->size)) avoid narrowing the operands on 32-bit
targets?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261101174911.25184-1-robin.clark@oss.qualcomm.com?part=1