From: Nadav Amit namit@vmware.com
Commit 824ddc601adc ("userfaultfd: provide unmasked address on page-fault") was introduced to fix an old bug, in which the offset in the address of a page-fault was masked. Concerns were raised - although were never backed by actual code - that some userspace code might break because the bug has been around for quite a while. To address these concerns a new flag was introduced, and only when this flag is set by the user, userfaultfd provides the exact address of the page-fault.
The commit however had a bug, and if the flag is unset, the offset was always masked based on a base-page granularity. Yet, for huge-pages, the behavior prior to the commit was that the address is masked to the huge-page granulrity.
While there are no reports on real breakage, fix this issue. If the flag is unset, use the address with the masking that was done before.
Fixes: 824ddc601adc ("userfaultfd: provide unmasked address on page-fault") Reported-by: James Houghton jthoughton@google.com Cc: Peter Xu peterx@redhat.com Cc: David Hildenbrand david@redhat.com Cc: Mike Rapoport rppt@linux.ibm.com Cc: Jan Kara jack@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: stable@vger.kernel.org Signed-off-by: Nadav Amit namit@vmware.com --- fs/userfaultfd.c | 12 +++++++----- 1 file changed, 7 insertions(+), 5 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c index e943370107d0..de86f5b2859f 100644 --- a/fs/userfaultfd.c +++ b/fs/userfaultfd.c @@ -192,17 +192,19 @@ static inline void msg_init(struct uffd_msg *msg) }
static inline struct uffd_msg userfault_msg(unsigned long address, + unsigned long real_address, unsigned int flags, unsigned long reason, unsigned int features) { struct uffd_msg msg; + msg_init(&msg); msg.event = UFFD_EVENT_PAGEFAULT;
- if (!(features & UFFD_FEATURE_EXACT_ADDRESS)) - address &= PAGE_MASK; - msg.arg.pagefault.address = address; + msg.arg.pagefault.address = (features & UFFD_FEATURE_EXACT_ADDRESS) ? + real_address : address; + /* * These flags indicate why the userfault occurred: * - UFFD_PAGEFAULT_FLAG_WP indicates a write protect fault. @@ -488,8 +490,8 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
init_waitqueue_func_entry(&uwq.wq, userfaultfd_wake_function); uwq.wq.private = current; - uwq.msg = userfault_msg(vmf->real_address, vmf->flags, reason, - ctx->features); + uwq.msg = userfault_msg(vmf->address, vmf->real_address, vmf->flags, + reason, ctx->features); uwq.ctx = ctx; uwq.waken = false;