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=1793801982; b=H2XLOQW/UyUtlVB3sSULXKlREzBhm4aax0BH4jVkfD8kESyMXv9E55IjAM00M2jdrUdI uoMs/U4W5x9ppYhyWluvx/T/BlX/EN10TbXQ+rWU8an1I2DZAOCBczy+budrFhFie2PQ2 hilPVk3LFHyffkWIoz1Jvu0CUegfBRHlIUL9N8mxesM9Bl8TD2cMaruKDnRrd4rJ0R5mV V5Rcf1xjHZx1FdHpFi0IVgdmtBdqZHyijuviQpBteVZNVtm+SW3cilRG3Hmr/p4JQJOKd kGv/YTYtDOgv1tij/wC2E6zNQ/n/xtzgPRNc8dtvd5hC6Zk6QqZPHlYnnWuKzt+DmvQ== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793801982; h=Received:DKIM-Signature:Subject:To:Cc:From:Date:Message-ID: MIME-Version:Content-Type:Content-Transfer-Encoding; bh=tlF+9rnlawkZ5OrsjV/fk8QYlOQYV6fcLwxgs3WlNtQ=; b=0kywTJNdGVuyY+aMlyBoI0pYdeH5Bd10QI9RFu7PFETZpjrlewaXMi8Bz7RyjQHIi6Cw 3AKcm04h+o8PHTv2qoQDRJj3BeerCYajWs7DWeHEUOvovM9JvicU91hmV05hnpBGRacaz i11HxiOp4BNU/Y+7EV3Vf+wsBDGCJmRsCDd9ZUK3DFZvGS/B+H3lWpSkVFx1IjIy8n4Dd TbrjfXqpWl2GJQ77iGbOE0uaO4+FCrxznv+kv/3sU4kgJUjFoEJIoukLwS7ptoiv2c7ku 93R4VZLvCgQ7UIdsZs9JxmUkGWkW3rsEuU2zlgMV8vi76AAH9pQVG6uGMo8xjIqRhNg== 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=OHkWHWdI; 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 7D2FB606A326 for ; Wed, 4 Nov 2026 14:19:42 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key, unprotected) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.a=rsa-sha256 header.s=korg header.b=OHkWHWdI Received: by smtp.kernel.org (Postfix) with ESMTPSA id 1676C1F00919; Wed, 4 Nov 2026 14:19:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1793801982; bh=tlF+9rnlawkZ5OrsjV/fk8QYlOQYV6fcLwxgs3WlNtQ=; h=Subject:To:Cc:From:Date; b=OHkWHWdIYFLeMiD8dgHjJq3DVPqhDElA2H5LWP1gFh+RSBAGNKAlcsElLUs+JKis0 D/MDbjBGKRhIHAVMFxsiotvOi8WI5D2hb4+BwfBythydcy22fEIp7lk86PNNCVCvcY JT+VV5BLfLoE9quv0OJDi7IvpA11BLP4BlAis3oU= Subject: FAILED: patch "[PATCH] mm: khugepaged: fix swap entry value to folio_pfn()" failed to apply to 6.12-stable tree To: yanglincheng@kylinos.cn,akpm@linux-foundation.org,baohua@kernel.org,david@kernel.org,dev.jain@arm.com,lance.yang@linux.dev,ljs@kernel.org,ryan.roberts@arm.com,stable@vger.kernel.org,zokeefe@google.com Cc: From: Date: Wed, 04 Nov 2026 15:19:34 +0100 Message-ID: <2026110434-getup-ongoing-7464@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-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.12-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . To reproduce the conflict and resubmit, you may use the following commands: git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.12.y git checkout FETCH_HEAD git cherry-pick -x 942c8ec27aa4ffc587511650718349964e1696e6 # git commit -s git send-email --to '' --in-reply-to '2026110434-getup-ongoing-7464@gregkh' --subject-prefix 'PATCH 6.12.y' 'HEAD^..' Possible dependencies: thanks, greg k-h ------------------ original commit in Linus's tree ------------------ >From 942c8ec27aa4ffc587511650718349964e1696e6 Mon Sep 17 00:00:00 2001 From: Vernon Yang Date: Wed, 9 Sep 2026 10:58:01 +0800 Subject: [PATCH] mm: khugepaged: fix swap entry value to folio_pfn() 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: diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h index 5a48c5406cce..7b526528f85b 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -178,10 +178,10 @@ 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) @@ -194,7 +194,7 @@ 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 75639298efc2..6380a12b8eee 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2683,6 +2683,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, int present, swap; int node = NUMA_NO_NODE; enum scan_result result = SCAN_SUCCEED; + unsigned long failed_pfn = -1; present = 0; swap = 0; @@ -2715,6 +2716,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, if (is_pmd_order(folio_order(folio))) { result = SCAN_PTE_MAPPED_HUGEPAGE; + failed_pfn = folio_pfn(folio); /* * PMD-sized THP implies that we can only try * retracting the PTE table. @@ -2726,6 +2728,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, node = folio_nid(folio); if (collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + failed_pfn = folio_pfn(folio); folio_put(folio); break; } @@ -2733,12 +2736,14 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, 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; } @@ -2773,7 +2778,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm, } } - 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; }