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[2003:cb:c705:7f00:8245:d031:7f8b:e004]) by smtp.gmail.com with ESMTPSA id d8-20020a1c7308000000b003ed1f6878a5sm14589794wmb.5.2023.03.21.12.36.36 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Mar 2023 12:36:36 -0700 (PDT) Message-ID: <44aae7fc-fb1f-b38e-bc17-504abf054e3f@redhat.com> Date: Tue, 21 Mar 2023 20:36:35 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.8.0 Subject: Re: [PATCH] mm/hugetlb: Fix uffd wr-protection for CoW optimization path To: Peter Xu , linux-mm@kvack.org, linux-kernel@vger.kernel.org Cc: Andrea Arcangeli , Andrew Morton , Axel Rasmussen , Mike Rapoport , Nadav Amit , Muhammad Usama Anjum , linux-stable References: <20230321191840.1897940-1-peterx@redhat.com> From: David Hildenbrand Organization: Red Hat In-Reply-To: <20230321191840.1897940-1-peterx@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: BAC0B4000D X-Stat-Signature: 38txkdbncitmcddm1jqqwmqiywc97wy3 X-HE-Tag: 1679427400-438728 X-HE-Meta: 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 e8S5tvOn 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 21.03.23 20:18, Peter Xu wrote: > This patch fixes an issue that a hugetlb uffd-wr-protected mapping can be > writable even with uffd-wp bit set. It only happens with all these > conditions met: (1) hugetlb memory (2) private mapping (3) original mapping > was missing, then (4) being wr-protected (IOW, pte marker installed). Then > write to the page to trigger. > > Userfaultfd-wp trap for hugetlb was implemented in hugetlb_fault() before > even reaching hugetlb_wp() to avoid taking more locks that userfault won't > need. However there's one CoW optimization path for missing hugetlb page > that can trigger hugetlb_wp() inside hugetlb_no_page(), that can bypass the > userfaultfd-wp traps. > > A few ways to resolve this: > > (1) Skip the CoW optimization for hugetlb private mapping, considering > that private mappings for hugetlb should be very rare, so it may not > really be helpful to major workloads. The worst case is we only skip the > optimization if userfaultfd_wp(vma)==true, because uffd-wp needs another > fault anyway. > > (2) Move the userfaultfd-wp handling for hugetlb from hugetlb_fault() > into hugetlb_wp(). The major cons is there're a bunch of locks taken > when calling hugetlb_wp(), and that will make the changeset unnecessarily > complicated due to the lock operations. > > (3) Carry over uffd-wp bit in hugetlb_wp(), so it'll need to fault again > for uffd-wp privately mapped pages. > > This patch chose option (3) which contains the minimum changeset (simplest > for backport) and also make sure hugetlb_wp() itself will start to be > always safe with uffd-wp ptes even if called elsewhere in the future. > > This patch will be needed for v5.19+ hence copy stable. > > Reported-by: Muhammad Usama Anjum > Cc: linux-stable > Fixes: 166f3ecc0daf ("mm/hugetlb: hook page faults for uffd write protection") > Signed-off-by: Peter Xu > --- > mm/hugetlb.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 8bfd07f4c143..22337b191eae 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5478,7 +5478,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, > struct folio *pagecache_folio, spinlock_t *ptl) > { > const bool unshare = flags & FAULT_FLAG_UNSHARE; > - pte_t pte; > + pte_t pte, newpte; > struct hstate *h = hstate_vma(vma); > struct page *old_page; > struct folio *new_folio; > @@ -5622,8 +5622,10 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma, > mmu_notifier_invalidate_range(mm, range.start, range.end); > page_remove_rmap(old_page, vma, true); > hugepage_add_new_anon_rmap(new_folio, vma, haddr); > - set_huge_pte_at(mm, haddr, ptep, > - make_huge_pte(vma, &new_folio->page, !unshare)); > + newpte = make_huge_pte(vma, &new_folio->page, !unshare); > + if (huge_pte_uffd_wp(pte)) > + newpte = huge_pte_mkuffd_wp(newpte); > + set_huge_pte_at(mm, haddr, ptep, newpte); > folio_set_hugetlb_migratable(new_folio); > /* Make the old page be freed below */ > new_folio = page_folio(old_page); Looks correct to me. Do we have a reproducer? Acked-by: David Hildenbrand -- Thanks, David / dhildenb