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authorNadav Amit <namit@vmware.com>2022-07-11 09:59:06 -0700
committerakpm <akpm@linux-foundation.org>2022-07-26 18:25:01 -0700
commitd172b1a3bd065dd89234eac547fc62cf80681631 (patch)
tree6e7a6d1a112a50d3607adcbd9787f2a08fe366ae
parentc80af0c250c8f8a3c978aa5aafbe9c39b336b813 (diff)
downloadlinux-d172b1a3bd065dd89234eac547fc62cf80681631.tar.bz2
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>
-rw-r--r--fs/userfaultfd.c12
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;