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ANDROID: 16K: Fixup padding vm_flags bits on VMA splits

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In some cases VMAs are split without the mmap write lock held;
later the lock is taken to fixup vm_flags of the original VMA.
Since some uppper bits of vm_flags are used to encode the ELF
padding ranges, they need to be modified on splits. This is
usually handled correctly by __split_vma(). However in the above
case, the flags get over witten later under the write lock.

Preserve vm_flag bits on reset to correctly represent padding.

Bug: 357901498
Change-Id: I1cb75419e614791a47cbdb0341373f619daf0bf2
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
This commit is contained in:
Kalesh Singh 2024-09-23 22:26:26 +00:00
parent 0e3d191eaf
commit 66aebe42e6
2 changed files with 4 additions and 3 deletions
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5
fs/userfaultfd.c
View File

@ -28,6 +28,7 @@
#include <linux/ioctl.h>
#include <linux/security.h>
#include <linux/hugetlb.h>
#include <linux/pgsize_migration.h>
int sysctl_unprivileged_userfaultfd __read_mostly;
@ -1511,7 +1512,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
* the current one has not been updated yet.
*/
vm_write_begin(vma);
WRITE_ONCE(vma->vm_flags, new_flags);
WRITE_ONCE(vma->vm_flags, vma_pad_fixup_flags(vma, new_flags));
rcu_assign_pointer(vma->vm_userfaultfd_ctx.ctx, ctx);
vm_write_end(vma);
@ -1694,7 +1695,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
* the current one has not been updated yet.
*/
vm_write_begin(vma);
WRITE_ONCE(vma->vm_flags, new_flags);
WRITE_ONCE(vma->vm_flags, vma_pad_fixup_flags(vma, new_flags));
rcu_assign_pointer(vma->vm_userfaultfd_ctx.ctx, NULL);
vm_write_end(vma);

2
mm/madvise.c
View File

@ -172,7 +172,7 @@ static long madvise_behavior(struct vm_area_struct *vma,
* vm_flags is protected by the mmap_lock held in write mode.
*/
vm_write_begin(vma);
WRITE_ONCE(vma->vm_flags, new_flags);
WRITE_ONCE(vma->vm_flags, vma_pad_fixup_flags(vma, new_flags));
vm_write_end(vma);
out_convert_errno: