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=1794061866; b=PLPzWEtKkAGF9HeQOtrfM0HwR6WUrSP4a41+/mK/BcBz2myp/mjMNXEv5C96giUbmOJE bYVjjmH6zIwWq02/L3YacVGR10Ys2MXYPOibhVAAMdbtzwhOJvvukN8HqK0euQ7kYrkJX GIQmq+fGcjyMU772IEMU8ZDMTW+IkzzXtY4WX+0ZKivJKiKkQBRIlmKkvbl+3fM5z/8FF 1gn9UdMCoVkNTmGKL5jb7rNONoF2e3sA652VlY4RIMHRD2Qm/kocm2iIkc+vbZDu1gh8u JP5peUHFziObvF8itGFl78qQ9mN/s031GlnRETASL5g98dxIaSsXEHAIV1ObnET1Umw== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1794061866; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:User-Agent:X-stable:X-Patchwork-Hint: MIME-Version:Content-Transfer-Encoding; bh=Po89/uq1dgyZAssOGrkZXfxImhU1SUTSVEsD14MbRuw=; b=OUByHKiyb89UlMAzSI67kYZ+5+/lKnfWDAWu5DuDmxTQvwc2DXw/R969slQJXNmj0n9Y Lx4aCfCznvzeOABeyvQnT/oAUGogO4/bvGImRBPb9rmTYLOzj/AhBfBPXUJ001ZYnUi2V AJGKsL7QNFZCquwQEHm9Rh0Gwm7U0s3DCTIrsfz3FZ/cOMJEULVDzIMecCrIQ33aKPwB4 tLi8V3boT45oR0CMgzo3Hq8YayGAcAqydrD1VQv9xJiAaoEFFx8N3zpr9MIPQuEj6BWRC cXY/q0DZL9MsiRBm/tWCeo5TKCDBr46YTT70xvJKg5fjK01cgsTjhmg1o4siQ/o9TEQ== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b="2E5r2a2/"; 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 BFAF7606A326; Sat, 7 Nov 2026 14:31:05 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=2E5r2a2/ Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6AFCA1F0089F; Sat, 7 Nov 2026 14:31:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1794061865; bh=Po89/uq1dgyZAssOGrkZXfxImhU1SUTSVEsD14MbRuw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=2E5r2a2/tHAFVKGKfBF4T6yurgOIMJQmT67+kuJQ9RbUSFR+n1f8QTlLUFgRqMKlK nz7qEhyl3rZFLOciSQfC0h1oy8WXQVG27FPjwNiDQZxhIc7ZIqyQ78CzSwrs//brq2 h6YD7EUycsHynbmXPNNWkO0Qb/uhexgyU+T6aZUk= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Vernon Yang , Andrew Morton , "David Hildenbrand (Arm)" , Barry Song , Dev Jain , Lance Yang , Lorenzo Stoakes , Ryan Roberts , Zach OKeefe , Sasha Levin Subject: [PATCH 6.12 0882/1536] mm: khugepaged: fix swap entry value to folio_pfn() Date: Sat, 7 Nov 2026 08:48:18 -0500 Message-ID: <20261107135022.401552473@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261107134957.653319350@linuxfoundation.org> References: <20261107134957.653319350@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore 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 6.12-stable review patch. If anyone has any objections, please let me know. ------------------ 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: adjusted PFN capture context for the existing scanner, which lacks temporary folio references and corresponding folio_put() calls ] 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 61967625c53d7..8f63af61c3ccb 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -174,10 +174,10 @@ 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) @@ -190,7 +190,7 @@ 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 0c111142e1e4d..7a54ce0f126bc 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2258,6 +2258,7 @@ 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; @@ -2283,6 +2284,7 @@ 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 @@ -2295,17 +2297,20 @@ 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); break; } cc->node_load[node]++; if (!folio_test_lru(folio)) { result = SCAN_PAGE_LRU; + failed_pfn = folio_pfn(folio); break; } if (!is_refcount_suitable(folio)) { result = SCAN_PAGE_COUNT; + failed_pfn = folio_pfn(folio); break; } @@ -2335,7 +2340,7 @@ 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; } #else -- 2.53.0