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=1793847227; b=NAbajLGPOfR5iWi7OTc+/tc9I1mvmotVpqMNQjK878VwiUwhWFV1tp8U3QI4TtLqws1k vm+5RLC2TDG2iU35ve1/Y55MqRAunP8bgfjSyHgxABmWTLBu2XpZ5D7b13yQrixrQLSWw 1eCmzgXQNdgqv9m0mQ9+rCoLiSzGZTalN9ABN5m64Johr6HdntYfgwU3gTVpYKYGTRvsL er+fgQAwKamhq07CRRT4mDT2wuXRZA/xn9yaOc+G5xFc7pL9mTNyoLozU5NrqqxZbdhyR Rz/HCig8TLyhsA1DYGQ6eLZMDMNg11nPu6t1lcUhxJYY/8rzDHZcJt3UY1XDaxAUY+Q== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793847227; h=Received:DKIM-Signature:From:To:Cc:Subject:Date:Message-ID:X-Mailer: In-Reply-To:References:MIME-Version:Content-Transfer-Encoding; bh=/m+V6Vw5N9+3ZSybFVk2sHvEnuvXOAoRTQQ/i6HhfLU=; b=MALyoC0oWRfqWvQBVTixQiF/NxDEzGfcHWWRcVZ6/M+DPQizSKst35u0K5idoj3a17jK Xz6fMlBq+UtDnr8X38hfkGDKOtnV+nBJzswA1XpIbq8NQANEKp58gnxWKrSNZwx7QdPmL h3rsCPPuRmrz+pyuNUALRfaNIUdAvG3nfZzj2P6kPlOF8g9G9sQCqWo9UxrBmXAc0ZdDx QMgWLxvaYaOBdnB60o/K3nKUg9SSU6H7x5ua8kVEtQWaR0OyymIjk1wKXxmQefihoBDg1 gmxHVe5W44Fd38ge2yGU2ooCG0E9FHrFlmO+IReo5KnaF789l1euXIshdFd/pKF5DOQ== 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=czVaYiiX; 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 E2EEE606A329 for ; Thu, 5 Nov 2026 02:53:46 +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=czVaYiiX Received: by smtp.kernel.org (Postfix) with ESMTPSA id A78011F000C1; Thu, 5 Nov 2026 02:53:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793847226; bh=/m+V6Vw5N9+3ZSybFVk2sHvEnuvXOAoRTQQ/i6HhfLU=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=czVaYiiXP14O288UQpOrruNhCJGmOGBvz/E7bA5PWjE21oQyDBiHcIca7T/5FvYuH u46aeRkiY+1Bbo7eW7EQQ2ml4MVK6RSipE2tIeBmGbJuAyCcqsDVfUztvnGII2W3L2 J6lWIpR0HSdya3Z8LM8SzclrYiGYRu/cF+6S3Vc0ETLOib40aEhq8ikppnHLFUvCzA nsBdC5a+J/mVUlRtyW/zKyij6GASsBfzPplHH8/LudKdqI9icFyrqe6UrLdmlI/Mj8 0ZHz8GtQ2Gzo8zeEvGzxOnvmrLyxeMZJQylxXkv6zcCRahwkg2ln33lPtep8wDJQVp LQI3W3I3U6bXQ== 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 6.1.y] mm: khugepaged: fix swap entry value to folio_pfn() Date: Wed, 4 Nov 2026 21:53:44 -0500 Message-ID: <20261105025324.1172108-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026110435-preview-regally-12b1@gregkh> References: <2026110435-preview-regally-12b1@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: adapted folio-based code to use struct page and page_to_pfn() 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 01591e7995235..23bd4c1f984e8 100644 --- a/include/trace/events/huge_memory.h +++ b/include/trace/events/huge_memory.h @@ -172,10 +172,10 @@ TRACE_EVENT(mm_collapse_huge_page_swapin, TRACE_EVENT(mm_khugepaged_scan_file, - TP_PROTO(struct mm_struct *mm, struct page *page, struct file *file, + TP_PROTO(struct mm_struct *mm, unsigned long pfn, struct file *file, int present, int swap, int result), - TP_ARGS(mm, page, file, present, swap, result), + TP_ARGS(mm, pfn, file, present, swap, result), TP_STRUCT__entry( __field(struct mm_struct *, mm) @@ -188,7 +188,7 @@ TRACE_EVENT(mm_khugepaged_scan_file, TP_fast_assign( __entry->mm = mm; - __entry->pfn = page ? page_to_pfn(page) : -1; + __entry->pfn = pfn; __assign_str(filename, file->f_path.dentry->d_iname); __entry->present = present; __entry->swap = swap; diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 4c3581364cb28..9738b70bbd453 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -2167,6 +2167,7 @@ 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; @@ -2200,6 +2201,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, /* Maybe PMD-mapped */ ? SCAN_PTE_MAPPED_HUGEPAGE : SCAN_PAGE_COMPOUND; + failed_pfn = page_to_pfn(page); /* * For SCAN_PTE_MAPPED_HUGEPAGE, further processing * by the caller won't touch the page cache, and so @@ -2212,18 +2214,21 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, node = page_to_nid(page); if (hpage_collapse_scan_abort(node, cc)) { result = SCAN_SCAN_ABORT; + failed_pfn = page_to_pfn(page); break; } cc->node_load[node]++; if (!PageLRU(page)) { result = SCAN_PAGE_LRU; + failed_pfn = page_to_pfn(page); break; } if (page_count(page) != 1 + page_mapcount(page) + page_has_private(page)) { result = SCAN_PAGE_COUNT; + failed_pfn = page_to_pfn(page); break; } @@ -2252,7 +2257,7 @@ static int hpage_collapse_scan_file(struct mm_struct *mm, unsigned long addr, } } - trace_mm_khugepaged_scan_file(mm, page, file, present, swap, result); + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, swap, result); return result; } #else -- 2.53.0