From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BD2F63B6344; Wed, 9 Sep 2026 06:58:37 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788937118; cv=none; b=MPU8A55stkq55rZP1ZNtvTGNe4x2lMDfNewpPetMcFyPEpTdu4ZjV5F25pXHBARxqdLhwD+8m4EEniaqz0Ve1Y6F1+Xkv/nsyF/XF0YFQf0gop2iDngHE+DGvUEh48CUnuE6ut1wo0PansoLojo/9RmcX8mrpR20kp3zLKkcnNo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788937118; c=relaxed/simple; bh=ZwcTGjsFBisObYo5p4yOAzzGAGhYTsp5VgaxYDbNmZ8=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=sN6P7YV7aTZKe5qZchLeFQ1UWyFLOGN3BRQ62klClVkbgx+i71orkEpUlrt3o16bpE2AFxaYo1quCoWEYrj/3KsgMf+juma2sX09TMCW+Mc3rVooy4lxrZBl8+UUNG4CVrn6bYTmrpynCK/6IOeJdyUmkKuWHj7LExNGe9tC5oA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b=fMrkjVgp; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux-foundation.org header.i=@linux-foundation.org header.b="fMrkjVgp" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B080D1F00A3D; Wed, 9 Sep 2026 06:58:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=korg; t=1788937117; bh=IqVLTnDYn66bK2YcqZfK0YLZ2dluSsDrOdyDou0m65A=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=fMrkjVgpFiPSguDCjRN3DHCdAH3a2In70srjXbI+JAYwfUX62P8hsZPd2kVEkeyMT ppciAQQLOoiEMj1nm71D9UG3Pj92Z+lOzUrGGp26ZH2SFpWv4pnRHQ7n2v+3vTRY4C mthRPk1QEDzNhBckcjx4e9AIERtNFGcQSHxfZr88= Date: Tue, 8 Sep 2026 23:58:36 -0700 From: Andrew Morton To: Vernon Yang Cc: david@kernel.org, ljs@kernel.org, nico.pache@linux.dev, ryan.roberts@arm.com, dev.jain@arm.com, baohua@kernel.org, lance.yang@linux.dev, usama.arif@linux.dev, zokeefe@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org, Vernon Yang Subject: Re: [PATCH v5 0/3] mm: khugepaged: fix tracepoint UAF Message-Id: <20260908235836.43865421771074b81eadd127@linux-foundation.org> In-Reply-To: <20260909025804.3233645-1-vernon2gm@gmail.com> References: <20260909025804.3233645-1-vernon2gm@gmail.com> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Wed, 9 Sep 2026 10:58:00 +0800 Vernon Yang wrote: > From: Vernon Yang > > 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(). Thanks, I've updated mm.git to this version. > V4 -> V5: > - Use a single trace statement. > - Collect Acked-by. Here's how v5 altered mm.git: mm/khugepaged.c | 15 ++++----------- 1 file changed, 4 insertions(+), 11 deletions(-) --- a/mm/khugepaged.c~b +++ a/mm/khugepaged.c @@ -1790,13 +1790,10 @@ out_unmap: unmapped, cc, enabled_orders); /* mmap_lock was released above, set lock_dropped */ *lock_dropped = true; - trace_mm_khugepaged_scan_pmd(mm, -1, referenced, none_or_zero, - SCAN_SUCCEED, unmapped); - } else { -out: - trace_mm_khugepaged_scan_pmd(mm, failed_pfn, referenced, - none_or_zero, result, unmapped); } +out: + trace_mm_khugepaged_scan_pmd(mm, failed_pfn, referenced, + none_or_zero, result, unmapped); return result; } @@ -2789,13 +2786,9 @@ static enum scan_result collapse_scan_fi } else { result = collapse_file(mm, addr, file, start, cc); } - trace_mm_khugepaged_scan_file(mm, -1, file, present, swap, - SCAN_SUCCEED); - } else { - trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, - swap, result); } + trace_mm_khugepaged_scan_file(mm, failed_pfn, file, present, swap, result); return result; } _