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Howlett" , Vlastimil Babka , Shakeel Butt , David Hildenbrand , Mike Rapoport , Michal Hocko , Uladzislau Rezki , Toshi Kani , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Kiryl Shutsemau , Catalin Marinas , Will Deacon , Dev Jain , Ryan Roberts , David Carlier , linux-mm@kvack.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, "Denis V. Lunev" , stable@vger.kernel.org, syzbot+fd95a72470f5a44e464c@syzkaller.appspotmail.com Subject: Re: [PATCH mm-hotfixes v5 0/5] mm: fix UAF caused by race between ptdump and vmap pgtable freeing Message-Id: <20260717122908.3d9f4a8ad76a748d859b43f2@linux-foundation.org> In-Reply-To: <20260717-series-vmap-race-fix-v5-0-606a0ac6d3e5@kernel.org> References: <20260717-series-vmap-race-fix-v5-0-606a0ac6d3e5@kernel.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: E3BAD80005 X-Stat-Signature: kn33f9qpe55fmaxxh6s5gs898qh7ntiy X-HE-Tag: 1784316550-526456 X-HE-Meta: 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 ipcJ/LeD d56gxVIJZT2hKD+bTuu7/aXWVAlMzv+8quoBc8eSQVHbafocawdQ8gAvyZTND5hRu+LF7egAF9dxRUEgO2ivswYbgJVLalfz7QQLM8jUkYLx1c28gDnAb+Y3tjS8Up4faBUwUK7QBRl6AyG87wktqZaw9/3kIuX1VpV+hfJ2mv2w7DqMTa+9iRw2s0leQq0mIfAVRq/z/y9dsbPvYFUyWjtcEwGytOoO3Q92driAgL7NH40LV/c6XET1pOqSP9yHrwDQ2xZ5wCB1p/AuiTQeQU8qVJtmpJ3IfuWeKQeozeLLFYbpM+yygMs61I3ZlyTCQ6eQAxIvdtAWbXLf7vqjUDYgMX/QiBo92MxNQbbPdimzyRf+rKQ7pXx7wTy7+JfsLbvxMtUGLKVBEu514W9troi/XYQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 17 Jul 2026 18:30:06 +0100 "Lorenzo Stoakes (ARM)" wrote: > Kernel page table walkers fall into two broad categories - those ranges > where no exclusion is required via walk_kernel_page_table_range_lockless() > and those where exclusion is required via walk_kernel_page_table_range() > or walk_page_range_debug(). > > The former category is used only by arm64 arch code operating on ranges it > both wholly owns and does not concurrently write. > > The latter category consists of kernel page table walkers operating on > ranges that are wholly owned (but which need exclusion against concurrent > writers). > > The lock used for exclusion is the mmap lock, and for kernel ranges this > the mmap lock on init_mm. > > ptdump is a special case being both the only user of > walk_page_range_debug(), and the only case in which it walks ranges it does > not own. > > This presents a problem, as page tables may be freed under ptdump. And > indeed there is a use-after-free bug in the kernel as a result, which this > series addresses. > > ... > > This series works around this by #ifndef CONFIG_ARM64'ing the mmap read > lock in vmap logic, then partially reverting commit fa93b45fd397 ("arm64: > Enable vmalloc-huge with ptdump"), keeping the enablement of huge vmap > support, and removing the ifdeffery with the partial revert patch. > Thanks, I updated mm-hotfixes-unstable to this version. > v5: > * Rebased on latest master of Linus's tree. > * Accumulated tags, thanks everybody! > * Added additional commit to fix race between CPA collapse/attribute set. > * Slight commit message tweaks. Here's how v5 altered mm.git. This is from the addition of [3/5] - no other patches changed. arch/x86/mm/pat/set_memory.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) --- a/arch/x86/mm/pat/set_memory.c~b +++ a/arch/x86/mm/pat/set_memory.c @@ -2122,7 +2122,9 @@ static int change_page_attr_set_clr(unsi cpa.curpage = 0; cpa.force_split = force_split; - ret = __change_page_attr_set_clr(&cpa, 1); + /* Avoid race with concurrent CPA collapse. */ + scoped_guard(mmap_read_lock, &init_mm) + ret = __change_page_attr_set_clr(&cpa, 1); /* * Check whether we really changed something: _