Commit dfc74e37 authored by Srinivasan Shanmugam's avatar Srinivasan Shanmugam Committed by Alex Deucher
Browse files

drm/amdkfd: Fix use-after-free of HMM range in svm_range_validate_and_map() 



The function svm_range_validate_and_map() was freeing `range` when
amdgpu_hmm_range_get_pages() failed. But later, the code still used the
same `range` pointer and freed it again. This could cause a
use-after-free and double-free issue.

The fix sets `range = NULL` right after it is freed and checks for
`range` before using or freeing it again.

v2: Removed duplicate !r check in the condition for clarity.

v3: In amdgpu_hmm_range_get_pages(), when hmm_range_fault() fails, we
kvfree(pfns) but leave the pointer in hmm_range->hmm_pfns still pointing
to freed memory. The caller (or amdgpu_hmm_range_free(range)) may try to
free range->hmm_range.hmm_pfns again, causing a double free, Setting
hmm_range->hmm_pfns = NULL immediately after kvfree(pfns) prevents both
double free. (Philip)

In svm_range_validate_and_map(), When r == 0, it means success → range
is not NULL.  When r != 0, it means failure → already made range = NULL.
So checking both (!r && range) is unnecessary because the moment r == 0,
we automatically know range exists and is safe to use. (Philip)

Fixes: 737da536 ("drm/amdgpu: update the functions to use amdgpu version of hmm")
Reported by: Dan Carpenter <dan.carpenter@linaro.org>
Cc: Philip Yang <Philip.Yang@amd.com>
Cc: Sunil Khatri <sunil.khatri@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: default avatarSrinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: default avatarPhilip <Yang&lt;Philip.Yang@amd.com>
Signed-off-by: default avatarAlex Deucher <alexander.deucher@amd.com>
parent 1017e393

drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c

+1 −0
Original line number Diff line number Diff line
@@ -221,6 +221,7 @@ int amdgpu_hmm_range_get_pages(struct mmu_interval_notifier *notifier, 


out_free_pfns:

	kvfree(pfns);

	hmm_range->hmm_pfns = NULL;

out_free_range:

	if (r == -EBUSY)

		r = -EAGAIN;

drivers/gpu/drm/amd/amdkfd/kfd_svm.c

+4 −2
Original line number Diff line number Diff line
@@ -1746,6 +1746,7 @@ static int svm_range_validate_and_map(struct mm_struct *mm, 
			WRITE_ONCE(p->svms.faulting_task, NULL);

			if (r) {

				amdgpu_hmm_range_free(range);

				range = NULL;

				pr_debug("failed %d to get svm range pages\n", r);

			}

		} else {
@@ -1763,7 +1764,7 @@ static int svm_range_validate_and_map(struct mm_struct *mm, 
		svm_range_lock(prange);



		/* Free backing memory of hmm_range if it was initialized

		 * Overrride return value to TRY AGAIN only if prior returns

		 * Override return value to TRY AGAIN only if prior returns

		 * were successful

		 */

		if (range && !amdgpu_hmm_range_valid(range) && !r) {
@@ -1771,6 +1772,7 @@ static int svm_range_validate_and_map(struct mm_struct *mm, 
			r = -EAGAIN;

		}

		/* Free the hmm range */

		if (range)

			amdgpu_hmm_range_free(range);