diff options
| author | Nadav Amit <namit@vmware.com> | 2022-07-11 09:59:06 -0700 |
|---|---|---|
| committer | akpm <akpm@linux-foundation.org> | 2022-07-26 18:25:01 -0700 |
| commit | d172b1a3bd065dd89234eac547fc62cf80681631 (patch) | |
| tree | 6e7a6d1a112a50d3607adcbd9787f2a08fe366ae /fs/userfaultfd.c | |
| parent | c80af0c250c8f8a3c978aa5aafbe9c39b336b813 (diff) | |
userfaultfd: provide properly masked address for huge-pages
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.
Link: https://lkml.kernel.org/r/20220711165906.2682-1-namit@vmware.com
Fixes: 824ddc601adc ("userfaultfd: provide unmasked address on page-fault")
Signed-off-by: Nadav Amit <namit@vmware.com>
Reported-by: James Houghton <jthoughton@google.com>
Reviewed-by: Mike Rapoport <rppt@linux.ibm.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Reviewed-by: James Houghton <jthoughton@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'fs/userfaultfd.c')
| -rw-r--r-- | fs/userfaultfd.c | 12 |
1 files 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; |