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Sun, 31 May 2026 19:14:12 -0700 (PDT) Received: from lima-ubuntu.hz.ali.com ([47.246.98.221]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45ef34a0374sm19735955f8f.2.2026.05.31.19.14.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 31 May 2026 19:14:11 -0700 (PDT) From: Qing Wang To: Nathan Chancellor , Nick Desaulniers , Bill Wendling , Justin Stitt , Peter Zijlstra , Thomas Gleixner , Mathieu Desnoyers , Ingo Molnar , Dmitry Vyukov , Mark Rutland Cc: linux-kernel@vger.kernel.org, llvm@lists.linux.dev, Qing Wang , syzbot+185a631927096f9da2fc@syzkaller.appspotmail.com Subject: [PATCH] rseq: fix using an uninitialized stack variable in rseq_exit_user_update Date: Mon, 1 Jun 2026 10:13:59 +0800 Message-Id: <20260601021359.3679327-1-wangqing7171@gmail.com> X-Mailer: git-send-email 2.34.1 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 | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/rseq_entry.h b/include/linux/rseq_entry.h index 63bc72086e75..e05f4c18f39e 100644 --- a/include/linux/rseq_entry.h +++ b/include/linux/rseq_entry.h @@ -638,8 +638,8 @@ static __always_inline bool rseq_exit_user_update(struct pt_regs *regs, struct t struct rseq_ids ids = { .cpu_id = task_cpu(t), .mm_cid = task_mm_cid(t), - .node_id = cpu_to_node(ids.cpu_id), }; + ids.node_id = cpu_to_node(ids.cpu_id); return rseq_update_usr(t, regs, &ids); efault: -- 2.34.1