linux-kernel - Re: [PATCH v6 00/11] Kernel address sanitizer

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Date:	Wed, 19 Nov 2014 15:41:02 +0300
From:	Andrey Ryabinin <a.ryabinin@...sung.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	Konstantin Serebryany <kcc@...gle.com>,
	Dmitry Chernenkov <dmitryc@...gle.com>,
	Andrey Konovalov <adech.fo@...il.com>,
	Yuri Gribov <tetra2005@...il.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Joonsoo Kim <iamjoonsoo.kim@....com>,
	Dave Hansen <dave.hansen@...el.com>,
	Andi Kleen <andi@...stfloor.org>,
	Vegard Nossum <vegard.nossum@...il.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Jones <davej@...hat.com>,
	Jonathan Corbet <corbet@....net>,
	Joe Perches <joe@...ches.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory
 debugger.

On 11/19/2014 03:44 AM, Sasha Levin wrote:
> On 11/18/2014 07:09 PM, Andrey Ryabinin wrote:
>> Yes with CONFIG_KASAN_INLINE you will get GPF instead of kasan report.
>> For userspaces addresses we don't have shadow memory. In outline case
>> I just check address itself before checking shadow. In inline case compiler
>> just checks shadow, so there is no way to avoid GPF.
>>
>> To be able to print report instead of GPF, I need to treat GPFs in a special
>> way if inline instrumentation was enabled, but it's not done yet.
> 
> I went ahead and tested it with the test module, which worked perfectly. No
> more complaints here...
> 
>>>> I remembered that one of the biggest changes in kasan was the introduction of
>>>> inline instrumentation, so I went ahead to disable it and see if it helps. But
>>>> the only result of that was having the boot process hang pretty early:
>>>>
>>>> [...]
>>>> [    0.000000] IOAPIC[0]: apic_id 21, version 17, address 0xfec00000, GSI 0-23
>>>> [    0.000000] Processors: 20
>>>> [    0.000000] smpboot: Allowing 24 CPUs, 4 hotplug CPUs
>>>> [    0.000000] e820: [mem 0xd0000000-0xffffffff] available for PCI devices
>>>> [    0.000000] Booting paravirtualized kernel on KVM
>>>> [    0.000000] setup_percpu: NR_CPUS:8192 nr_cpumask_bits:24 nr_cpu_ids:24 nr_node_ids:1
>>>> [    0.000000] PERCPU: Embedded 491 pages/cpu @ffff8808dce00000 s1971864 r8192 d31080 u2097152
>>>> *HANG*
>>>>
>> This hang happens only with your error patch above or even without it?
> 
> It happens even without the patch.
> 

I took your config from "Replace _PAGE_NUMA with PAGE_NONE protections" thread.
I've noticed that you have both KASAN and UBSAN enabled.
I didn't try them together, though it could work with patch bellow.
But it should hang much earlier then you see, without this patch.

------------------------------------------------------
From: Andrey Ryabinin <a.ryabinin@...sung.com>
Subject: [PATCH] kasan: don't use ubsan's instrumentation for kasan internals

kasan do unaligned access for checking shadow memory faster.
If ubsan is also enabled this will lead to unbound recursion:
__asan_load* -> __ubsan_handle_type_mismatch -> __asan_load* -> ...

Disable ubsan's instrumentation for kasan.c to avoid that.

Signed-off-by: Andrey Ryabinin <a.ryabinin@...sung.com>
---
 mm/kasan/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
index ef2d313..2b53073 100644
--- a/mm/kasan/Makefile
+++ b/mm/kasan/Makefile
@@ -1,4 +1,5 @@
 KASAN_SANITIZE := n
+UBSAN_SANITIZE := n

 # Function splitter causes unnecessary splits in __asan_load1/__asan_store1
 # see: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63533
-- 
2.1.3

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