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[2001:1ae9:1c2:4c00:748:2a9a:a2a6:1362]) by smtp.gmail.com with ESMTPSA id c19-20020a05600c0a5300b003c21ba7d7d6sm1348138wmq.44.2022.11.03.07.25.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 03 Nov 2022 07:25:06 -0700 (PDT) From: Andrew Jones To: x86@kernel.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org Subject: [PATCH v4 1/1] x86: cpuinfo: Ensure inputs to cpumask_next are valid Date: Thu, 3 Nov 2022 15:25:04 +0100 Message-Id: <20221103142504.278543-2-ajones@ventanamicro.com> X-Mailer: git-send-email 2.37.3 In-Reply-To: <20221103142504.278543-1-ajones@ventanamicro.com> References: <20221103142504.278543-1-ajones@ventanamicro.com> MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Jonas Bonn , linux-s390@vger.kernel.org, Alexander Gordeev , Albert Ou , Vasily Gorbik , Yury Norov , Heiko Carstens , Dave Hansen , Stefan Kristiansson , Ingo Molnar , Borislav Petkov , Paul Walmsley , Palmer Dabbelt , Thomas Gleixner , linuxppc-dev@lists.ozlabs.org, Stafford Horne , openrisc@lists.librecores.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" The valid cpumask range is [0, nr_cpu_ids) and cpumask_next() currently calls find_next_bit() with its input CPU ID number plus one for the bit number, giving cpumask_next() the range [-1, nr_cpu_ids - 1). seq_read_iter() and cpuinfo's start and next seq operations implement a pattern like n = cpumask_next(n - 1, mask); show(n); while (1) { ++n; n = cpumask_next(n - 1, mask); if (n >= nr_cpu_ids) break; show(n); } which will eventually result in cpumask_next() being called with nr_cpu_ids - 1. A kernel compiled with commit 78e5a3399421 ("cpumask: fix checking valid cpu range"), but not its revert, commit 80493877d7d0 ("Revert "cpumask: fix checking valid cpu range"."), will generate a warning when DEBUG_PER_CPU_MAPS is enabled each time /proc/cpuinfo is read. Future-proof cpuinfo by checking its input to cpumask_next() is valid. Signed-off-by: Andrew Jones Cc: Yury Norov --- arch/x86/kernel/cpu/proc.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kernel/cpu/proc.c b/arch/x86/kernel/cpu/proc.c index 099b6f0d96bd..de3f93ac6e49 100644 --- a/arch/x86/kernel/cpu/proc.c +++ b/arch/x86/kernel/cpu/proc.c @@ -153,6 +153,9 @@ static int show_cpuinfo(struct seq_file *m, void *v) static void *c_start(struct seq_file *m, loff_t *pos) { + if (*pos == nr_cpu_ids) + return NULL; + *pos = cpumask_next(*pos - 1, cpu_online_mask); if ((*pos) < nr_cpu_ids) return &cpu_data(*pos); -- 2.37.3