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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) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 1FBFC20003 X-Rspam-User: X-Stat-Signature: re8zo6bgnzc6o7ck1h7zhjpz6te8pocf X-HE-Tag: 1788937117-71999 X-HE-Meta: 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 CvQHp7xA 3GX7UO2YJXTu8WrJEJnPgk1ah3XDuyPlHfSfW4wM7NejqOYdoQsigmeBt2dcwxArp9PJd0PrNuxabcDtMYZVK4xc7H6rWKmYvoP4331xvWhKhElW15Ajn9WaWrAw4T46BAFASgSiL5ZUQdGowY9JL0mp9aR3FMvstgvqNeQuV2E3hkzJ0wHetrpp1PEkKYWvSDM4nqum9Rojv7DdUnSsooi1UCe0sksxWiGYCRiS5hmzTich3M3455vYZgIdJVsXZzNR8RoWooU/u0Mf6940GjMb2vg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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; } _