From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Fix the ordering to restore the map before the folio is freed.
Cc: stable@vger.kernel.org Reported-by: Google Big Sleep big-sleep-vuln-reports@google.com Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKr... Signed-off-by: Lance Yang lance.yang@linux.dev --- mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c index c1bd9a4b663d..37f6d1097853 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) __folio_mark_uptodate(folio); err = filemap_add_folio(mapping, folio, offset, gfp); if (unlikely(err)) { - folio_put(folio); /* * If a split of large page was required, it * already happened when we marked the page invalid * which guarantees that this call won't fail */ set_direct_map_default_noflush(folio_page(folio, 0)); + folio_put(folio); if (err == -EEXIST) goto retry;
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Cc: stable@vger.kernel.org Reported-by: Google Big Sleep big-sleep-vuln-reports@google.com Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKr... Signed-off-by: Lance Yang lance.yang@linux.dev
mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c index c1bd9a4b663d..37f6d1097853 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) __folio_mark_uptodate(folio); err = filemap_add_folio(mapping, folio, offset, gfp); if (unlikely(err)) {
folio_put(folio); /* * If a split of large page was required, it * already happened when we marked the page invalid * which guarantees that this call won't fail */ set_direct_map_default_noflush(folio_page(folio, 0));
folio_put(folio); if (err == -EEXIST) goto retry;2.49.0
On 31.10.25 10:59, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Fully agreed
Acked-by: David Hildenbrand david@redhat.com
On 2025/10/31 18:19, David Hildenbrand wrote:
On 31.10.25 10:59, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Fully agreed
Acked-by: David Hildenbrand david@redhat.com
Cheers!
Small thing, sorry to be a pain buuuut could we please not send patches in-reply to another mail, it makes it harder for people to see :)
On Fri, Oct 31, 2025 at 11:59:16AM +0200, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Agree with David, Mike this looks 'obviously correct' thanks for addressing it.
But also as per Mike, please update message accordingly and send v2 not-in-reply-to-anything :P
With that said:
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
Cc: stable@vger.kernel.org Reported-by: Google Big Sleep big-sleep-vuln-reports@google.com Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKr... Signed-off-by: Lance Yang lance.yang@linux.dev
mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c index c1bd9a4b663d..37f6d1097853 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) __folio_mark_uptodate(folio); err = filemap_add_folio(mapping, folio, offset, gfp); if (unlikely(err)) {
folio_put(folio); /* * If a split of large page was required, it * already happened when we marked the page invalid * which guarantees that this call won't fail */ set_direct_map_default_noflush(folio_page(folio, 0));
folio_put(folio); if (err == -EEXIST) goto retry;-- 2.49.0
-- Sincerely yours, Mike.
On 2025/10/31 18:24, Lorenzo Stoakes wrote:
Small thing, sorry to be a pain buuuut could we please not send patches in-reply to another mail, it makes it harder for people to see :)
On Fri, Oct 31, 2025 at 11:59:16AM +0200, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Agree with David, Mike this looks 'obviously correct' thanks for addressing it.
But also as per Mike, please update message accordingly and send v2 not-in-reply-to-anything :P
Sure. V2 is on the way ;)
With that said:
Reviewed-by: Lorenzo Stoakes lorenzo.stoakes@oracle.com
Thanks! Lance
Cc: stable@vger.kernel.org Reported-by: Google Big Sleep big-sleep-vuln-reports@google.com Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKr... Signed-off-by: Lance Yang lance.yang@linux.dev
mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c index c1bd9a4b663d..37f6d1097853 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) __folio_mark_uptodate(folio); err = filemap_add_folio(mapping, folio, offset, gfp); if (unlikely(err)) {
folio_put(folio); /* * If a split of large page was required, it * already happened when we marked the page invalid * which guarantees that this call won't fail */ set_direct_map_default_noflush(folio_page(folio, 0));
folio_put(folio); if (err == -EEXIST) goto retry;-- 2.49.0
-- Sincerely yours, Mike.
On 2025/10/31 17:59, Mike Rapoport wrote:
On Fri, Oct 31, 2025 at 05:18:18PM +0800, Lance Yang wrote:
From: Lance Yang lance.yang@linux.dev
The error path in secretmem_fault() frees a folio before restoring its direct map status, which is a race leading to a panic.
Let's use the issue description from the report:
Will do. I'll also add the missing Fixes: tag.
When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping.
If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping.
If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault.
Fix the ordering to restore the map before the folio is freed.
... restore the direct map
With these changes
Reviewed-by: Mike Rapoport (Microsoft) rppt@kernel.org
Thanks! Lance
Cc: stable@vger.kernel.org Reported-by: Google Big Sleep big-sleep-vuln-reports@google.com Closes: https://lore.kernel.org/linux-mm/CAEXGt5QeDpiHTu3K9tvjUTPqo+d-=wuCNYPa+6sWKr... Signed-off-by: Lance Yang lance.yang@linux.dev
mm/secretmem.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/secretmem.c b/mm/secretmem.c index c1bd9a4b663d..37f6d1097853 100644 --- a/mm/secretmem.c +++ b/mm/secretmem.c @@ -82,13 +82,13 @@ static vm_fault_t secretmem_fault(struct vm_fault *vmf) __folio_mark_uptodate(folio); err = filemap_add_folio(mapping, folio, offset, gfp); if (unlikely(err)) {
folio_put(folio); /* * If a split of large page was required, it * already happened when we marked the page invalid * which guarantees that this call won't fail */ set_direct_map_default_noflush(folio_page(folio, 0));
folio_put(folio); if (err == -EEXIST) goto retry;2.49.0
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