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Wed, 14 Oct 2026 16:30:50 +0000 X-Mizu-Trace-ID: b89656d6ed486c36 X-Migadu-Flow: FLOW_OUT From: Lance Yang To: david@kernel.org Cc: akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, huang.ying.caritas@gmail.com, baolin.wang@linux.alibaba.com, baohua@kernel.org, ryan.roberts@arm.com, hanchuanhua@oppo.com, kas@kernel.org, kylebot@openai.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH] mm: fix address wraparound when scanning large folio PTEs Date: Thu, 15 Oct 2026 00:30:43 +0800 Message-ID: <20261014163043.39233-1-lance.yang@linux.dev> X-Mailer: git-send-email 2.49.0 In-Reply-To: <20261013-folio_pte_scan_range-v1-1-c50dc30bf6ad@kernel.org> References: <20261013-folio_pte_scan_range-v1-1-c50dc30bf6ad@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: BEC8310000E X-Stat-Signature: hb118nkzixpxk7814591ugmikad4ycid X-HE-Tag: 1791995451-311903 X-HE-Meta: U2FsdGVkX1/Sy8c2c6tUAls8XnBgbpjglRdEGHfZcWeIeELyr8+oxnNHA99gguVSmPZ+kX0NfMlW7IXAvsPfnm4Tof4fdBwhkdTRBglqdp1Fm12AAG1DfwH4iS00vFESPKxZrpE8GRhusLMNbVI/vRWF7s5oPlxlMcndEkkzvKD4WyZJnTSvK/yNAuXZoWjS+BHsiaAMZ6uOerhW5Hcvb590GFdICFvWBBJxaveBPDuMnERxGCEEAbiziBPCTzcQRNv1BYmMb1kjN4JpGS77BANZsoev8ElQR+uT19amyGHvM3rI45ti+abYr6AD3kt4h54tRtnj+Jq+gj2JirgAAyPaH0cGqVOwEKm8BnPQln5fsA2AKjGwbK3NvaDFi5tEPAWsoQckumbCoz/+02mFii1UWgWnLWgHgeiJadlouEmHtsxoZt088chIY0rbQ1pxeoLm7KyQKM9QoGpuHk8bpf4Ucmnb3lnGAxMdizNXjpLus+p64AJnR0qlcynjOjKbDIaGY6BckbyL69jG8jsC9qWb9WiP5wqWzIOTaMLAfsv1XMQvaBVnyCf5e3PO7sGQgBbkJ0ThE1fohJUvKDIoaB5ai7BmwLoSYXzZYw5wlQkbd63KAIWE01wBEeQ/uDoTK/cXL5eTZHkS98Y0CocbTZYKAM4FtBVikfeE/Xca8nkI/vZWYy0szedZlDJEnQjHi722HYzojuDJS8rEPDMyJEDmcgpQLcC/tCpsNgiZW9K8mT8PpLkACw4C2yi+zHs4owgX/0JRLkCiJKMPsVIUyO9ygA+OlBlh19XXbXvfPaXXXYEyIA6rKI5v5bXbv9aUyHRCH40secFv9TUa7QJ8Zd41wLBoYBm+ALkGddYUmbo5HBemXrwb2sY1ZCyXB+dL618CyZllxZ2m/hAeZz0Xw1ASiqbixaRERwsbG7oAdn2KegxPKZxLAj5oqKn11uPbiRjYNBQ3y8d9SYB69pW vG8NEYDr 6pAPsKWA82lPZd+UhcHUlX5C4HM3dbQ5AfYCoLbSy2/Nhx2nBM2L0+dZKyhQL9OLgM+MNc7zB/D7qAhol7U42lh46vt/86ueRh1WSAUBaeXmzk/CwNMjCN55qs9kVWu0mBUkMkUPlWbvMUdz6K9+dYB1APv937NwEKaH90PfcGn2Pf9zfU0/SBUzua/mHw2HhDuULQmOjEpf48TMYLlRsUvXQC7xyWuq9jXMtYGVtka1ki4Hxs2DPDt72iwkppddz5PDFes7/gePx4xGnyZyA3E/GnSFX/JW76o/lFPvj/l4tb2dBFdbtZAp8vbl6dRrML9w6texBVW003qiI/4by9czav2nI/Do9hQBH3G/kiO0K43Q= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Oct 13, 2026 at 02:30:37PM +0200, David Hildenbrand (Arm) wrote: >numa_rebuild_large_mapping() and do_swap_page() can be tricked into >generating an address wraparound, crashing the kernel. All that's required >is to map a tail page of a large folio close enough to the start/end of >the address space to e.g., make > > unsigned long addr_start = addr - (nr << PAGE_SHIFT); > >to wrap around. > >Let's fix it by providing a better helper, folio_pte_scan_range(), that >takes care of staying within VMA and page table boundaries while >handling possible wraparounds. > >Reported-by: Kyle Zeng >Fixes: d2136d749d76 ("mm: support multi-size THP numa balancing") >Fixes: 508758960b8d ("mm: swap: entirely map large folios found in swapcache") >Cc: stable@vger.kernel.org >Signed-off-by: David Hildenbrand (Arm) >--- > mm/memory.c | 43 +++++++++++++++++++++++++++++-------------- > 1 file changed, 29 insertions(+), 14 deletions(-) > >diff --git a/mm/memory.c b/mm/memory.c >index 1f5d5f7d39cd2..a3823010aa981 100644 >--- a/mm/memory.c >+++ b/mm/memory.c >@@ -4933,6 +4933,27 @@ static void check_swap_exclusive(struct folio *folio, swp_entry_t entry, > } while (--nr_pages); > } > >+/* >+ * Get the address range in which a folio might be mapped, assuming its pages >+ * are mapped consecutively and the folio page at the given idx is mapped at >+ * the given address. >+ */ >+static void folio_pte_scan_range(const struct folio *folio, >+ const struct vm_area_struct *vma, unsigned long addr, >+ unsigned long idx, unsigned long *start, unsigned long *end) >+{ >+ /* Stay within the page table and VMA boundaries. */ >+ const unsigned long pmd_start = addr & PMD_MASK; >+ const unsigned long pmd_end = pmd_start + PMD_SIZE; >+ const unsigned long lower = max(pmd_start, vma->vm_start); >+ const unsigned long upper = min(pmd_end - 1, vma->vm_end - 1) + 1; That -1/+1 threw me for a sec ... Neat little trick! >+ const unsigned long offset = idx << PAGE_SHIFT; >+ >+ /* Avoid any address wraparounds. */ >+ *start = addr - min(addr - lower, offset); >+ *end = addr + min(upper - addr, folio_size(folio) - offset); >+} >+ > /* > * We enter with either the VMA lock or the mmap_lock held (see > * FAULT_FLAG_VMA_LOCK), and pte mapped but not yet locked. >@@ -5121,16 +5142,15 @@ vm_fault_t do_swap_page(struct vm_fault *vmf) > address = vmf->address; > ptep = vmf->pte; > if (folio_test_large(folio) && folio_test_swapcache(folio)) { >- int nr = folio_nr_pages(folio); >- unsigned long idx = folio_page_idx(folio, page); >- unsigned long folio_start = address - idx * PAGE_SIZE; >- unsigned long folio_end = folio_start + nr * PAGE_SIZE; >+ const int nr = folio_nr_pages(folio); >+ const unsigned long idx = folio_page_idx(folio, page); >+ unsigned long folio_start, folio_end; > pte_t *folio_ptep; > pte_t folio_pte; > >- if (unlikely(folio_start < max(address & PMD_MASK, vma->vm_start))) >- goto check_folio; >- if (unlikely(folio_end > pmd_addr_end(address, vma->vm_end))) >+ folio_pte_scan_range(folio, vma, address, idx, &folio_start, >+ &folio_end); >+ if (unlikely((folio_end - folio_start) >> PAGE_SHIFT != nr)) > goto check_folio; > > folio_ptep = vmf->pte - idx; >@@ -6280,16 +6300,11 @@ static void numa_rebuild_large_mapping(struct vm_fault *vmf, struct vm_area_stru > struct folio *folio, pte_t fault_pte, > bool ignore_writable, bool pte_write_upgrade) > { >- int nr = pte_pfn(fault_pte) - folio_pfn(folio); >+ const unsigned long idx = pte_pfn(fault_pte) - folio_pfn(folio); > unsigned long start, end, addr = vmf->address; >- unsigned long addr_start = addr - (nr << PAGE_SHIFT); >- unsigned long pt_start = ALIGN_DOWN(addr, PMD_SIZE); > pte_t *start_ptep; > >- /* Stay within the VMA and within the page table. */ >- start = max3(addr_start, pt_start, vma->vm_start); >- end = min3(addr_start + folio_size(folio), pt_start + PMD_SIZE, >- vma->vm_end); >+ folio_pte_scan_range(folio, vma, addr, idx, &start, &end); > start_ptep = vmf->pte - ((addr - start) >> PAGE_SHIFT); > > /* Restore all PTEs' mapping of the large folio */ > >--- Nothing jumped out at me, feel free to add: Reviewed-by: Lance Yang