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=1793837326; b=ZCDWeFxnv9GBoYjzJ0kT8ux+WbEDybDT3V7pgweb7fcJO6daSR9pMJF1rJoy7JDwt6Ub z2NoRI+gmSBh2+riL5xBp4haK+D6QHmRiDR1JNkgau6kTX3y77saRa/wDJehdC4iJli2y yhr5w+p3qAG1+4z6b5k2kXa2IalGi9qiLd8vywaDJC5fS4A4E50EQuR37eptBsQOeEV/0 JrE7VHZs2rKY9frXpns3bHBz9auMSAsxWkpBTdZ/v2RjwSnU8deZxvnhmFcMvQi/oOGdu Cajd7igFsE0r9Tj5X3hcYvNrf2iL4LSzgGshTHcha1DU+MqLdIj71OCPtPB1liNTflA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793837326; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=AoyI8+js6CBTlPGFphhIf16cjOV74ltgmCtIRebKI5E=; b=n9APBfLtAR0mNP5HAOOrE1SW2wrOwNR15MruqSlGz5zUV3mzJe/0IoftvsQKHfF58tuJ TeGyQUAKCkHsIlFA35UaAHNQa+/QWtsT4/ZLgBcz7AHabSXvyyIi8rENQ+xdlJFyxbWBr YPIClGca77L6lQQU1ewRyQOFKZehDHvWsajuOEQH3atdFR46NuU3w8S48DYpsKChBmfbS QtjvbFkw9X+O6ICJ71Vu71R4QdYRrLbxMEAGZYZOidUO32u7DV5HJM09pt4EIPVc02XYp UszvcR09D51/pAYrasoj7Wu2ZjcTA/a3jQ9/FBQi9iLWNdNEz5a6I1E2q7itUE5xnEw== 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=XzWPfN87; 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 B92FE606A329 for ; Thu, 5 Nov 2026 00:08:45 +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=XzWPfN87 Received: by smtp.kernel.org (Postfix) with ESMTPSA id 416981F000C1; Thu, 5 Nov 2026 00:08:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793837325; bh=AoyI8+js6CBTlPGFphhIf16cjOV74ltgmCtIRebKI5E=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=XzWPfN87P1BOvgfZziYNKMrXR2hmzSY5/DJ3vJH9LivWaRPtH9yqbEeR4TOtgdyUb 4B/FcMcCWwi5zjRlx8ipjj83lNmQkW8mpaOvNwhHAdL1XB8qqN8DXtQ/hKYFKzLESy fjG+i56tXN12VeV5rZ2mN3po47vy1X4C9c7eiNba/D4TimQAAoLGIR/f9E2dnCUQzM muhHpiXgU6hW5pfrQIHdcaZ50nZ8ugRdGROtMlqc2Td2czmuiOuXWIJOtbwanzBcBO MQl04+a28/ZMFTEBvujIE6tCL+o3PJKYEPU06t6udh1GU+YAtEr27RTW3UoC2vouNP uwzxU001zrTAA== 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 6.12.y] mm: khugepaged: fix swap entry value to folio_pfn() Date: Wed, 4 Nov 2026 19:08:42 -0500 Message-ID: <20261105000826.927011-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110434-getup-ongoing-7464@gregkh> References: <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-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: 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