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Mon, 01 Jun 2026 20:09:04 -0700 (PDT) From: Qing Wang To: peterz@infradead.org, mathieu.desnoyers@efficios.com Cc: dvyukov@google.com, justinstitt@google.com, linux-kernel@vger.kernel.org, llvm@lists.linux.dev, mark.rutland@arm.com, mingo@kernel.org, morbo@google.com, nathan@kernel.org, nick.desaulniers+lkml@gmail.com, syzbot+185a631927096f9da2fc@syzkaller.appspotmail.com, tglx@kernel.org, wangqing7171@gmail.com Subject: [PATCH v2] rseq: fix using an uninitialized stack variable in rseq_exit_user_update Date: Tue, 2 Jun 2026 11:08:54 +0800 Message-Id: <20260602030854.574038-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260601143934.GT3493090@noisy.programming.kicks-ass.net> References: <20260601143934.GT3493090@noisy.programming.kicks-ass.net> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit There is an bug which is an uninitialized stack variable use in `rseq_exit_user_update()` reported by syzbot: BUG: KMSAN: kernel-infoleak in rseq_set_ids_get_csaddr include/linux/rseq_entry.h:502 [inline] The local variable: ```c struct rseq_ids ids = { .cpu_id = task_cpu(t), .mm_cid = task_mm_cid(t), .node_id = cpu_to_node(ids.cpu_id), }; ``` According to the C standard, the evaluation order of expressions in an initializer list is indeterminately sequenced. The compiler (Clang, in this KMSAN build) evaluates `cpu_to_node(ids.cpu_id)` *before* `ids.cpu_id` is initialized with `task_cpu(t)`. This is fixed by moving the assignment of ids.node_id outside the structure initialization. Reported-by: syzbot+185a631927096f9da2fc@syzkaller.appspotmail.com Closes: https://syzkaller.appspot.com/bug?extid=185a631927096f9da2fc Fixes: 82f572449cfe ("rseq: Implement read only ABI enforcement for optimized RSEQ V2 mode") Signed-off-by: Qing Wang --- include/linux/rseq_entry.h | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/include/linux/rseq_entry.h b/include/linux/rseq_entry.h index 63bc72086e75..ed9da6e41a2a 100644 --- a/include/linux/rseq_entry.h +++ b/include/linux/rseq_entry.h @@ -635,10 +635,11 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t return true; } + int cpu = task_cpu(t); struct rseq_ids ids = { - .cpu_id = task_cpu(t), + .cpu_id = cpu, .mm_cid = task_mm_cid(t), - .node_id = cpu_to_node(ids.cpu_id), + .node_id = cpu_to_node(cpu), }; return rseq_update_usr(t, regs, &ids); -- 2.34.1