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Thu, 27 Aug 2026 22:59:47 -0700 (PDT) Received: from localhost.localdomain ([240e:b8f:1df9:a600:c693:b19f:ada0:748]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-396b0ea808csm5826241a91.2.2026.08.27.22.59.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Aug 2026 22:59:46 -0700 (PDT) From: Vernon Yang To: akpm@linux-foundation.org, david@kernel.org, ljs@kernel.org Cc: 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: [PATCH v4 0/3] mm: khugepaged: fix tracepoint UAF Date: Fri, 28 Aug 2026 13:59:23 +0800 Message-ID: <20260828055926.346744-1-vernon2gm@gmail.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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(). This series is based on mm-new. V3 -> V4: - Only trace the PFN if it really was problematic. - Calling the respective trace_xxx() functions separately on success and failure. - Set new_pfn once after successful alloc_charge_folio(). V2 -> V3: - Place folio_pfn() inside the xas_for_each() loop in PATCH#1. - Already defaulted the pfn value to -1, to simple it in PATCH#2. V1 -> V2: - Instead of passing the folio, just pass the pfn directly. - Using the folio_pfn() before dropping the reference or the page table lock. V3 : https://lore.kernel.org/linux-mm/20260824092935.73892-1-vernon2gm@gmail.com/ V2 : https://lore.kernel.org/linux-mm/20260815051924.194810-1-vernon2gm@gmail.com/ V1 : https://lore.kernel.org/linux-mm/20260811133655.267739-1-vernon2gm@gmail.com/ Vernon Yang (3): mm: khugepaged: fix swap entry value to folio_pfn() mm: khugepaged: fix folio is used after pte_unmap_unlock() mm: khugepaged: fix folio is used after folio_put/unlock() include/trace/events/huge_memory.h | 18 ++++++++--------- mm/khugepaged.c | 32 +++++++++++++++++++++++++----- 2 files changed, 36 insertions(+), 14 deletions(-) base-commit: 1a46b1e97bde62afa7d925bb0dcd9f9748a1d7c3 -- 2.53.0