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

[Sasha Levin]

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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