Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory debugger.

[Andrey Ryabinin]

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@xxxxxxxxxxx>
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@xxxxxxxxxxx>
---
 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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