6.8-stable review patch. If anyone has any objections, please let me know.
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From: Ryan Roberts ryan.roberts@arm.com
commit c70dce4982ce1718bf978a35f8e26160b82081f4 upstream.
make_uffd_wp_pte() was previously doing:
pte = ptep_get(ptep); ptep_modify_prot_start(ptep); pte = pte_mkuffd_wp(pte); ptep_modify_prot_commit(ptep, pte);
But if another thread accessed or dirtied the pte between the first 2 calls, this could lead to loss of that information. Since ptep_modify_prot_start() gets and clears atomically, the following is the correct pattern and prevents any possible race. Any access after the first call would see an invalid pte and cause a fault:
pte = ptep_modify_prot_start(ptep); pte = pte_mkuffd_wp(pte); ptep_modify_prot_commit(ptep, pte);
Link: https://lkml.kernel.org/r/20240429114017.182570-1-ryan.roberts@arm.com Fixes: 52526ca7fdb9 ("fs/proc/task_mmu: implement IOCTL to get and optionally clear info about PTEs") Signed-off-by: Ryan Roberts ryan.roberts@arm.com Acked-by: David Hildenbrand david@redhat.com Cc: Muhammad Usama Anjum usama.anjum@collabora.com Cc: Peter Xu peterx@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- fs/proc/task_mmu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1826,7 +1826,7 @@ static void make_uffd_wp_pte(struct vm_a pte_t old_pte;
old_pte = ptep_modify_prot_start(vma, addr, pte); - ptent = pte_mkuffd_wp(ptent); + ptent = pte_mkuffd_wp(old_pte); ptep_modify_prot_commit(vma, addr, pte, old_pte, ptent); } else if (is_swap_pte(ptent)) { ptent = pte_swp_mkuffd_wp(ptent);