From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=100.103.45.18 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793833952; b=DgN/+raUoYirAFxzoAq2qnBLLEA0GF1ldbXGadhJPo70R3wmbraZd1czZRljbmHDC75I CG+wNhdeXOTof7urSg9k+XUx7Yhb6wgHfjxoHDKm6Cv2azyM+sZXnNm5i5/7LVlcRQeC8 W+pjZ4jr9owHsg/Jho31al0fLHAy9n4H5oaFqFmGwYosw54RkZw4zBGj2xv/DJcYaruRV z4/Pjs0PMrRkmN6F/EjsBkxM952mX6CKKAcligXmhlNZPWmerAzhIfi56h0E0Xnjoz5lF CnsiFdJW47NOOI4O/nQMWmEE6+tZpbL7lG0u4SWy399VlX1XcPhj+RiDUBxGEp8VhKQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793833952; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=Kc5FNT8++8zqjv9Uv42gVmOP5Qoeo3jVa983URMnBnA=; b=QRjGvRmSwJf2Xy+DUMVwgNqbiFJH43s/g6aU//ZMegY5CFow1uGGpar5FsoaR9O/y+XE Mm4DO3VKJ9kHcOh5SmpGQsdwHe+YKvUo+kxK5scF1fXJ2Dd1f9r4J61TRZJxXQ43KGve+ C5qrmycKFLaXqrfpi0CQO2/ZoZD5UD1prLNCBWXXabJXFbdI9EFoGDfyK4dpNiU88mHV7 PD/zXanKInd2NYNi8TcRTdvHJDnB7DdzonKsTpIcumi/pfnVsWP1TqxXeIMRSA6LkPjB4 Jwg1uJEon4IQg0kYAQgJupqC9yLTh6hhPNt0LubmcPBtSDr7mOXogNHxcAV1ivX9gQQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=jGfDXfBJ; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 70D76606A31B for ; Wed, 4 Nov 2026 23:12:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=jGfDXfBJ Received: by smtp.kernel.org (Postfix) with ESMTPSA id D9B0A1F000C1; Wed, 4 Nov 2026 23:12:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793833952; bh=Kc5FNT8++8zqjv9Uv42gVmOP5Qoeo3jVa983URMnBnA=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=jGfDXfBJdLex5ZXTfDhQ2WQEvMj8ZdXUTSjodnVt6rT22nqOo6peRLK+eQ6/QzJ0Q 3dnXBD1jfGEas4BVIQpxTMIxBrcytPeANF/awmbNRndXrCxE9OY5MQQV8bx6VQo2j6 SwgdnZa2RDYvj8QFndfxa6wCycx7YJrDwISM1VsW9PLdtvwjLqQuz0SVnEYZmNAVH0 Uk+8ZRH0AY+L/3a2a2HJuiHfWCrhcWpEFHbAlaIlhbH/jKufs0mpmydfkN3AyaLbE7 KCAWqJDNObe8s6Y/YKxR4U8CSCx4ihGNwPYEJTUC7kIgGGYCchDVtcuhjt6yzgQD6Q Mkqf2O+ZcDQcQ== From: Sasha Levin To: stable@vger.kernel.org Cc: Vernon Yang , Andrew Morton , "David Hildenbrand (Arm)" , Barry Song , Dev Jain , Lance Yang , Lorenzo Stoakes , Ryan Roberts , Zach O'Keefe , Sasha Levin Subject: [PATCH 6.18.y] mm: khugepaged: fix swap entry value to folio_pfn() Date: Wed, 4 Nov 2026 18:12:29 -0500 Message-ID: <20261104231213.892598-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110433-example-husband-50dd@gregkh> References: <2026110433-example-husband-50dd@gregkh> X-Mailing-List: stable@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Vernon Yang [ Upstream commit 942c8ec27aa4ffc587511650718349964e1696e6 ] Patch series "mm: khugepaged: fix tracepoint UAF", v5. The khugepaged tracepoints take a folio pointer and call folio_pfn(), but by then the folio may no longer be valid: freed after folio_put(), folio_unlock() or pte_unmap_unlock(), or not a folio at all but an xarray-encoded swap entry. On classic SPARSEMEM, dereferencing it oopses khugepaged as soon as the trace event is enabled; on other memory models it merely prints a bogus pfn. Pass the pfn to the tracepoints directly, captured while the folio is still pinned, closing the use-after-free windows in mm_khugepaged_scan_file(), mm_khugepaged_scan_pmd() and mm_khugepaged_collapse_file(). This patch (of 3): When the swap entries found exceed max_ptes_swap, the loop is left via break with folio still holding the xarray value that encodes the swap entry, not valid folio pointer. That value is passed to trace_mm_khugepaged_scan_file(), which feeds it to folio_pfn(). On FLATMEM and SPARSEMEM_VMEMMAP, the page_to_pfn() is plain pointer arithmetic, so the trace event merely prints bogus scan_pfn. On classic SPARSEMEM, the page_to_pfn() reads page->flags, dereferencing the tiny encoded integer and oopsing khugepaged whenever the trace event is enabled. So when folio is the swap entry value, simply set pfn to -1, just like exhausted scan naturally. And the folio_put() has maybe dropped the last reference of folio. The trace_mm_khugepaged_scan_file() is left with a dangling folio pointer. so using the folio_pfn() before dropping the reference, closing use-after-free window. Link: https://lore.kernel.org/20260909025804.3233645-1-vernon2gm@gmail.com Link: https://lore.kernel.org/20260909025804.3233645-2-vernon2gm@gmail.com Fixes: d41fd2016ed0 ("mm/khugepaged: add tracepoint to hpage_collapse_scan_file()") Signed-off-by: Vernon Yang Signed-off-by: Andrew Morton Acked-by: David Hildenbrand (Arm) Cc: Barry Song Cc: Dev Jain Cc: Lance Yang Cc: Lorenzo Stoakes Cc: Ryan Roberts Cc: Zach O'Keefe Cc: [ sashal: Retained int result instead of enum scan_result in hpage_collapse_scan_file(). ] Signed-off-by: Sasha Levin --- include/trace/events/huge_memory.h | 6 +++--- mm/khugepaged.c | 7 ++++++- 2 files changed, 9 insertions(+), 4 deletions(-) diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 2276614691dfd..1464d45c90abf 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -167,10 +167,10 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, TRACE_EVENT(mm_khugepaged_scan_file, - TP_PROTO(struct mm_struct *mm, struct folio *folio, struct file *file, + TP_PROTO(struct mm_struct *mm, unsigned long pfn, struct file *file, int present, int swap, int result), - TP_ARGS(mm, folio, file, present, swap, result), + TP_ARGS(mm, pfn, file, present, swap, result), TP_STRUCT__entry( __field(struct mm_struct *, mm) @@ -183,7 +183,7 @@ TRACE_EVENT(mm_khugepaged_scan_file, TP_fast_assign( __entry->mm = mm; - __entry->pfn = folio ? folio_pfn(folio) : -1; + __entry->pfn = pfn; __assign_str(filename); __entry->present = present; __entry->swap = swap; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index e2ac26c05064f..cc3a09a0c2596 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2308,6 +2308,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, int present, swap; int node = NUMA_NO_NODE; int result = SCAN_SUCCEED; + unsigned long failed_pfn = -1; present = 0; swap = 0; @@ -2344,6 +2345,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, folio->index == start) { /* Maybe PMD-mapped */ result = SCAN_PTE_MAPPED_HUGEPAGE; + failed_pfn = folio_pfn(folio); /* * For SCAN_PTE_MAPPED_HUGEPAGE, further processing * by the caller won't touch the page cache, and so @@ -2357,6 +2359,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, node = folio_nid(folio); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } @@ -2364,12 +2367,14 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, if (!folio_test_lru(folio)) { result = SCAN_PAGE_LRU; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } if (folio_expected_ref_count(folio) + 1 != folio_ref_count(folio)) { result = SCAN_PAGE_COUNT; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } @@ -2401,7 +2406,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, } } - trace_mm_khugepaged_scan_file(mm, folio, file, present, swap, result); + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, swap, result); return result; } -- 2.53.0