lkml.org 
[lkml]   [2024]   [Jan]   [11]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
Subject[PATCH 1/1] userfaultfd: avoid huge_zero_page in UFFDIO_MOVE
From
While testing UFFDIO_MOVE ioctl, syzbot triggered VM_BUG_ON_PAGE caused
by a call to PageAnonExclusive() with a huge_zero_page as a parameter.
UFFDIO_MOVE does not yet handle zeropages and returns EBUSY when one is
encountered. Add an early huge_zero_page check in the PMD move path
to avoid this situation.

Reported-by: syzbot+705209281e36404998f6@syzkaller.appspotmail.com
Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
---
Applies cleanly over linux-next, mm-stable and mm-unstable branches

mm/userfaultfd.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index 216ab4c8621f..20e3b0d9cf7e 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1393,6 +1393,12 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, struct mm_struct *mm,
err = -ENOENT;
break;
}
+ /* Avoid moving zeropages for now */
+ if (is_huge_zero_pmd(*src_pmd)) {
+ spin_unlock(ptl);
+ err = -EBUSY;
+ break;
+ }

/* Check if we can move the pmd without splitting it. */
if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) ||
--
2.43.0.275.g3460e3d667-goog

\
 
 \ /
  Last update: 2024-01-12 02:40    [W:0.020 / U:0.164 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site