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From: Dmitry Vyukov <dvyukov@google.com>
To: Ingo Molnar <mingo@kernel.org>
Cc: Andy Lutomirski <luto@kernel.org>,
	Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Alexander Potapenko <glider@google.com>,
	"x86@kernel.org" <x86@kernel.org>, Borislav Petkov <bp@alien8.de>,
	LKML <linux-kernel@vger.kernel.org>,
	Brian Gerst <brgerst@gmail.com>, Oleg Nesterov <oleg@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: [PATCH v6 1/3] fork: Add generic vmalloced stack support
Date: Wed, 24 Aug 2016 09:11:58 -0700	[thread overview]
Message-ID: <CACT4Y+Zr70+xJUGGDzih09ELG2+SFRKuH9Asvyeo0+RWPT3sKw@mail.gmail.com> (raw)
In-Reply-To: <20160824100352.GA9681@gmail.com>

On Wed, Aug 24, 2016 at 3:03 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Andy Lutomirski <luto@kernel.org> wrote:
>
>> +config VMAP_STACK
>> +     default y
>> +     bool "Use a virtually-mapped stack"
>> +     depends on HAVE_ARCH_VMAP_STACK && !KASAN
>> +     ---help---
>> +       Enable this if you want the use virtually-mapped kernel stacks
>> +       with guard pages.  This causes kernel stack overflows to be
>> +       caught immediately rather than causing difficult-to-diagnose
>> +       corruption.
>> +
>> +       This is presently incompatible with KASAN because KASAN expects
>> +       the stack to map directly to the KASAN shadow map using a formula
>> +       that is incorrect if the stack is in vmalloc space.
>
> Btw., is this KASAN limitation fundamental?
>
> As x86 is going to enable this feature by default, this probably limits KASAN
> utility rather significantly.


No, it's not fundamental.

KASAN has shadow for vmalloc range, but currently we map a single
read-only zero page there (which means "this memory is good"). Stack
instrumentation tries to write to that read-only page, which causes
crash.

Andrey proposed that we can map some real writable pages in the shadow
range when we allocate a vmalloc-ed stack:
https://groups.google.com/d/msg/kasan-dev/0YxqFs9r0V8/OKoGHQL8BAAJ

  reply	other threads:[~2016-08-24 16:12 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-11  9:35 [PATCH v6 0/3] virtually mapped stacks Andy Lutomirski
2016-08-11  9:35 ` [PATCH v6 1/3] fork: Add generic vmalloced stack support Andy Lutomirski
2016-08-15 11:55   ` Michal Hocko
2016-08-24 10:03   ` Ingo Molnar
2016-08-24 16:11     ` Dmitry Vyukov [this message]
2016-08-24 13:02   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-08-24 16:51   ` [PATCH v6 1/3] " Josh Cartwright
2016-08-30 22:01     ` Andy Lutomirski
2016-08-30 22:26       ` Josh Cartwright
2016-08-11  9:35 ` [PATCH v6 2/3] dma-api: Teach the "DMA-from-stack" check about vmapped stacks Andy Lutomirski
2016-08-24 13:02   ` [tip:x86/asm] " tip-bot for Andy Lutomirski
2016-08-11  9:35 ` [PATCH v6 3/3] x86/mm/64: Enable " Andy Lutomirski
2016-08-24 13:03   ` [tip:x86/asm] x86/mm/64: Enable vmapped stacks (CONFIG_HAVE_ARCH_VMAP_STACK=y) tip-bot for Andy Lutomirski
2016-10-21 12:32     ` Matt Fleming
2016-10-21 12:32       ` Matt Fleming
2016-10-22  0:18       ` Andy Lutomirski
2016-10-22  0:18         ` Andy Lutomirski
2016-10-24 13:09         ` Matt Fleming
2016-10-24 13:09           ` Matt Fleming
2016-10-30 16:21           ` Andy Lutomirski
2016-10-30 16:21             ` Andy Lutomirski
2016-11-07 12:32             ` Matt Fleming
2016-11-07 12:32               ` Matt Fleming
2016-08-20 18:06 ` [PATCH v6 0/3] virtually mapped stacks Andy Lutomirski
2016-08-24 10:12   ` Ingo Molnar
2016-08-24 15:27     ` Andy Lutomirski
2016-08-24 17:16       ` Ingo Molnar

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