| Message ID | 20240926154234.2247217-1-david@redhat.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v1] mm/huge_memory: check pmd_special() only after pmd_present() | expand |
On Thu, Sep 26, 2024 at 05:42:34PM +0200, David Hildenbrand wrote: > We should only check for pmd_special() after we made sure that we > have a present PMD. For example, if we have a migration PMD, > pmd_special() might indicate that we have a special PMD although we > really don't. > > This fixes confusing migration entries as PFN mappings, and not > doing what we are supposed to do in the "is_swap_pmd()" case further > down in the function -- including messing up COW, page table handling > and accounting. > > Reported-by: syzbot+bf2c35fa302ebe3c7471@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/lkml/66f15c8d.050a0220.c23dd.000f.GAE@google.com/ > Fixes: bc02afbd4d73 ("mm/fork: accept huge pfnmap entries") > Cc: Peter Xu <peterx@redhat.com> > Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Peter Xu <peterx@redhat.com>
On 26.09.24 17:42, David Hildenbrand wrote: > We should only check for pmd_special() after we made sure that we > have a present PMD. For example, if we have a migration PMD, > pmd_special() might indicate that we have a special PMD although we > really don't. > > This fixes confusing migration entries as PFN mappings, and not > doing what we are supposed to do in the "is_swap_pmd()" case further > down in the function -- including messing up COW, page table handling > and accounting. > > Reported-by: syzbot+bf2c35fa302ebe3c7471@syzkaller.appspotmail.com > Closes: https://lore.kernel.org/lkml/66f15c8d.050a0220.c23dd.000f.GAE@google.com/ > Fixes: bc02afbd4d73 ("mm/fork: accept huge pfnmap entries") > Cc: Peter Xu <peterx@redhat.com> > Signed-off-by: David Hildenbrand <david@redhat.com> > --- > > I yet have to do more testing, but sending this out already. Testing looks good. Andrew please queue this, it's a rather unpleasent behavior if we fork() with a PMD migration entry that should be fixed upstream soonish :) (no idea how I could have missed CCing Andrew once more)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c index 0580ac9e47b9..e55efcad1e6c 100644 --- a/mm/huge_memory.c +++ b/mm/huge_memory.c @@ -1586,7 +1586,7 @@ int copy_huge_pmd(struct mm_struct *dst_mm, struct mm_struct *src_mm, int ret = -ENOMEM; pmd = pmdp_get_lockless(src_pmd); - if (unlikely(pmd_special(pmd))) { + if (unlikely(pmd_present(pmd) && pmd_special(pmd))) { dst_ptl = pmd_lock(dst_mm, dst_pmd); src_ptl = pmd_lockptr(src_mm, src_pmd); spin_lock_nested(src_ptl, SINGLE_DEPTH_NESTING);
We should only check for pmd_special() after we made sure that we have a present PMD. For example, if we have a migration PMD, pmd_special() might indicate that we have a special PMD although we really don't. This fixes confusing migration entries as PFN mappings, and not doing what we are supposed to do in the "is_swap_pmd()" case further down in the function -- including messing up COW, page table handling and accounting. Reported-by: syzbot+bf2c35fa302ebe3c7471@syzkaller.appspotmail.com Closes: https://lore.kernel.org/lkml/66f15c8d.050a0220.c23dd.000f.GAE@google.com/ Fixes: bc02afbd4d73 ("mm/fork: accept huge pfnmap entries") Cc: Peter Xu <peterx@redhat.com> Signed-off-by: David Hildenbrand <david@redhat.com> --- I yet have to do more testing, but sending this out already. --- mm/huge_memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)