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

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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: 737da5363c ("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: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Philip Yang<Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Srinivasan Shanmugam 2025-10-23 19:54:16 +05:30 committed by Alex Deucher
parent 1017e393ad
commit dfc74e37bd
2 changed files with 5 additions and 2 deletions
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1
drivers/gpu/drm/amd/amdgpu/amdgpu_hmm.c
View File

@ -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;

6
drivers/gpu/drm/amd/amdkfd/kfd_svm.c
View File

@ -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) {
@ -1771,7 +1772,8 @@ static int svm_range_validate_and_map(struct mm_struct *mm,
r = -EAGAIN;
}
/* Free the hmm range */
amdgpu_hmm_range_free(range);
if (range)
amdgpu_hmm_range_free(range);
if (!r && !list_empty(&prange->child_list)) {