From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Mark Rutland <mark.rutland@arm.com>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>
Cc: <akpm@linux-foundation.org>, <hpa@linux.intel.com>,
<mingo@kernel.org>, <tglx@linutronix.de>,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Catalin Marinas <catalin.marinas@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: [PATCH] arm64: kasan: clear stale stack poison
Date: Fri, 26 Feb 2016 17:00:50 +0300 [thread overview]
Message-ID: <56D05A92.7070802@virtuozzo.com> (raw)
In-Reply-To: <1455816458-19485-1-git-send-email-mark.rutland@arm.com>
On 02/18/2016 08:27 PM, Mark Rutland wrote:
> This patch is a followup to the discussion in [1].
>
> When using KASAN and CPU idle and/or CPU hotplug, KASAN leaves the stack shadow
> poisoned on exit from the kernel, and this poison is later hit when a CPU is
> brought online and reuses that portion of the stack. Hitting the poison depends
> on stackframe layout, so the bug only manifests in some configurations.
>
> I think that the hotplug issue is generic, and x86 is affected. I couldn't spot
> magic around idle, so x86 may be fine there. It would be great if someone
> familiar with the x86 code could prove/disprove either of those assertions.
>
> If x86 is affected, it likely makes sense to unpoison the stack in common code
> prior to bringing a CPU online to avoid that.
>
I think x86 need that unpoisoning. do_boot_cpu() resets stack for secondary cpu,
so it could be possible to hit stale shadow.
static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle)
{
....
idle->thread.sp = (unsigned long) (((struct pt_regs *)
(THREAD_SIZE + task_stack_page(idle))) - 1);
early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(cpu);
initial_code = (unsigned long)start_secondary;
stack_start = idle->thread.sp;
> For idle I'm not keen on having to perform a memset of THREAD_SIZE/8 every time
> a CPU re-enters the kernel. I don't yet have numbers for how bad that is, but
> it doesn't sound good.
>
> Thanks,
> Mark.
>
> [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2016-February/408961.html
>
prev parent reply other threads:[~2016-02-26 14:01 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-18 17:27 Mark Rutland
2016-02-18 17:54 ` Catalin Marinas
2016-02-18 18:03 ` Will Deacon
2016-02-18 18:13 ` Catalin Marinas
2016-02-19 10:52 ` Lorenzo Pieralisi
2016-02-19 11:35 ` Mark Rutland
2016-02-26 14:00 ` Andrey Ryabinin [this message]
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