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

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Date:	Tue, 18 Nov 2014 18:38:14 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>, akpm@...ux-foundation.org
CC:	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,
	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>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 00/11] Kernel address sanitizer - runtime memory debugger.

Hi Andrey,

After the recent exchange of mails about kasan it came to me that I haven't
seen a kasan warning for a while now. To give kasan a quick test I added a rather
simple error which should generate a kasan warning about accessing userspace
memory (yes, I know kasan has a test module but my setup doesn't like modules):

	diff --git a/net/socket.c b/net/socket.c
	index fe20c31..794e9f4 100644
	--- a/net/socket.c
	+++ b/net/socket.c
	@@ -1902,7 +1902,7 @@ SYSCALL_DEFINE5(setsockopt, int, fd, int, level, int, optname,
	 {
	        int err, fput_needed;
	        struct socket *sock;
	-
	+       *((char *)10) = 5;
	        if (optlen < 0)
	                return -EINVAL;

A gfp was triggered, but no kasan warning was shown.

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*

I'm using the latest gcc:

$ gcc --version
gcc (GCC) 5.0.0 20141117 (experimental)


I'll continue looking into it tomorrow, just hoping it rings a bell...


Thanks,
Sasha
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