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Date: Thu, 20 Jul 2017 09:36:18 +0100
From: James Morse <james.morse@....com>
To: Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC: Laura Abbott <labbott@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Kernel Hardening <kernel-hardening@...ts.openwall.com>,
"linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Takahiro Akashi <akashi.takahiro@...aro.org>,
Catalin Marinas <catalin.marinas@....com>,
Dave Martin <dave.martin@....com>,
Laura Abbott <labbott@...oraproject.org>,
Will Deacon <will.deacon@....com>,
Kees Cook <keescook@...omium.org>
Subject: Re: Re: [RFC PATCH 6/6] arm64: add VMAP_STACK
and detect out-of-bounds SP
Hi Ard,
On 20/07/17 06:35, Ard Biesheuvel wrote:
> On 20 July 2017 at 00:32, Laura Abbott <labbott@...hat.com> wrote:
>> I didn't notice any performance impact but I also wasn't trying that
>> hard. I did try this with a different configuration and ran into
>> stackspace errors almost immediately:
>>
>> [ 0.358026] smp: Brought up 1 node, 8 CPUs
>> [ 0.359359] SMP: Total of 8 processors activated.
>> [ 0.359542] CPU features: detected feature: 32-bit EL0 Support
>> [ 0.361781] Insufficient stack space to handle exception!
[...]
>> [ 0.367382] Task stack: [0xffffff8008e80000..0xffffff8008e84000]
>> [ 0.367519] IRQ stack: [0xffffffc03bf62000..0xffffffc03bf66000]
>
> The IRQ stack is not 16K aligned ...
>> [ 0.367687] ESR: 0x00000000 -- Unknown/Uncategorized
>> [ 0.367868] FAR: 0x0000000000000000
>> [ 0.368059] Kernel panic - not syncing: kernel stack overflow
>> [ 0.368252] CPU: 4 PID: 0 Comm: swapper/4 Not tainted 4.12.0-00018-ge9cf49d604ef-dirty #23
>> [ 0.368427] Hardware name: linux,dummy-virt (DT)
>> [ 0.368612] Call trace:
>> [ 0.368774] [<ffffff8008087fd8>] dump_backtrace+0x0/0x228
>> [ 0.368979] [<ffffff80080882c8>] show_stack+0x10/0x20
>> [ 0.369270] [<ffffff80084602dc>] dump_stack+0x88/0xac
>> [ 0.369459] [<ffffff800816328c>] panic+0x120/0x278
>> [ 0.369582] [<ffffff8008088b40>] handle_bad_stack+0xd0/0xd8
>> [ 0.369799] [<ffffff80080bfb94>] __do_softirq+0x74/0x210
>> [ 0.370560] SMP: stopping secondary CPUs
>> [ 0.384269] Rebooting in 5 seconds..
>>
>> The config is based on what I use for booting my Hikey android
>> board. I haven't been able to narrow down exactly which
>> set of configs set this off.
>>
>
> ... so for some reason, the percpu atom size change fails to take effect here.
I'm not completely up to speed with these series, so this may be noise:
When we added the IRQ stack Jungseok Lee discovered that alignment greater than
PAGE_SIZE only applies to CPU0. Secondary CPUs read the per-cpu init data into a
page-aligned area, but any greater alignment requirement is lost.
Because of this the irqstack was only 16byte aligned, and struct thread_info had
to be be discovered without depending on stack alignment.
Thanks,
James
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