From: Yury Norov <yury.norov@gmail.com>
To: Andrew Jones <ajones@ventanamicro.com>
Cc: Jonas Bonn <jonas@southpole.se>,
linux-s390@vger.kernel.org,
Alexander Gordeev <agordeev@linux.ibm.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Vasily Gorbik <gor@linux.ibm.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Heiko Carstens <hca@linux.ibm.com>,
x86@kernel.org, linux-kernel@vger.kernel.org,
openrisc@lists.librecores.org, Ingo Molnar <mingo@redhat.com>,
Borislav Petkov <bp@alien8.de>,
Paul Walmsley <paul.walmsley@sifive.com>,
Palmer Dabbelt <palmer@dabbelt.com>,
linux-riscv@lists.infradead.org, linuxppc-dev@lists.ozlabs.org,
Thomas Gleixner <tglx@linutronix.de>,
Albert Ou <aou@eecs.berkeley.edu>
Subject: Re: [PATCH v4 1/1] x86: cpuinfo: Ensure inputs to cpumask_next are valid
Date: Thu, 10 Nov 2022 20:14:56 -0800 [thread overview]
Message-ID: <Y23MQA8ZaQ135aJV@yury-laptop> (raw)
In-Reply-To: <20221103142504.278543-2-ajones@ventanamicro.com>
On Thu, Nov 03, 2022 at 03:25:04PM +0100, Andrew Jones wrote:
> 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 <ajones@ventanamicro.com>
> Cc: Yury Norov <yury.norov@gmail.com>
Reviewed-by: Yury Norov <yury.norov@gmail.com>
> ---
> 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
prev parent reply other threads:[~2022-11-11 4:15 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-03 14:25 [PATCH v4 0/1] Fix /proc/cpuinfo cpumask warning Andrew Jones
2022-11-03 14:25 ` [PATCH v4 1/1] x86: cpuinfo: Ensure inputs to cpumask_next are valid Andrew Jones
2022-11-11 4:14 ` Yury Norov [this message]
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