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[2003:d8:2f49:bc00:12fa:1681:c754:1630]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-459e587e154sm116116445e9.27.2025.08.07.12.42.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 07 Aug 2025 12:42:48 -0700 (PDT) Message-ID: <43f91e3e-84c5-4fd1-9b63-4e2cb28dab36@redhat.com> Date: Thu, 7 Aug 2025 21:42:47 +0200 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 1/1] userfaultfd: fix a crash in UFFDIO_MOVE when PMD is a migration entry To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, peterx@redhat.com, aarcange@redhat.com, lokeshgidra@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com, stable@vger.kernel.org References: <20250806220022.926763-1-surenb@google.com> <3eba855a-740c-4423-b2ed-24d622af29a5@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 07.08.25 17:27, Suren Baghdasaryan wrote: > On Thu, Aug 7, 2025 at 3:31 AM David Hildenbrand wrote: >> >> On 07.08.25 00:00, Suren Baghdasaryan wrote: >>> When UFFDIO_MOVE encounters a migration PMD entry, it proceeds with >>> obtaining a folio and accessing it even though the entry is swp_entry_t. >>> Add the missing check and let split_huge_pmd() handle migration entries. >>> >>> Fixes: adef440691ba ("userfaultfd: UFFDIO_MOVE uABI") >>> Reported-by: syzbot+b446dbe27035ef6bd6c2@syzkaller.appspotmail.com >>> Closes: https://lore.kernel.org/all/68794b5c.a70a0220.693ce.0050.GAE@google.com/ >>> Signed-off-by: Suren Baghdasaryan >>> Reviewed-by: Peter Xu >>> Cc: stable@vger.kernel.org >>> --- >>> Changes since v3 [1] >>> - Updated the title and changelog, per Peter Xu >>> - Added Reviewed-by: per Peter Xu >>> >>> [1] https://lore.kernel.org/all/20250806154015.769024-1-surenb@google.com/ >>> >>> mm/userfaultfd.c | 17 ++++++++++------- >>> 1 file changed, 10 insertions(+), 7 deletions(-) >>> >>> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c >>> index 5431c9dd7fd7..116481606be8 100644 >>> --- a/mm/userfaultfd.c >>> +++ b/mm/userfaultfd.c >>> @@ -1826,13 +1826,16 @@ ssize_t move_pages(struct userfaultfd_ctx *ctx, unsigned long dst_start, >>> /* Check if we can move the pmd without splitting it. */ >>> if (move_splits_huge_pmd(dst_addr, src_addr, src_start + len) || >>> !pmd_none(dst_pmdval)) { >>> - struct folio *folio = pmd_folio(*src_pmd); >>> - >>> - if (!folio || (!is_huge_zero_folio(folio) && >>> - !PageAnonExclusive(&folio->page))) { >>> - spin_unlock(ptl); >>> - err = -EBUSY; >>> - break; >>> + /* Can be a migration entry */ >>> + if (pmd_present(*src_pmd)) { >>> + struct folio *folio = pmd_folio(*src_pmd); >>> + >>> + if (!folio >> >> >> How could you get !folio here? That only makes sense when calling >> vm_normal_folio_pmd(), no? > > Yes, I think you are right, this check is not needed. I can fold it > into this fix or post a separate cleanup patch. I'm guessing a > separate patch would be better? I think you can just post a fixup inline here and ask Andrew to squash it. He will shout if he wants a completely new version :) -- Cheers, David / dhildenb