linux-kernel - Re: perf_fuzzer compiled for x32 causes reboot

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.10.1402241030500.19768@vincent-weaver-1.um.maine.edu>
Date:	Mon, 24 Feb 2014 10:35:34 -0500 (EST)
From:	Vince Weaver <vincent.weaver@...ne.edu>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	Vince Weaver <vincent.weaver@...ne.edu>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, "H.J. Lu" <hjl.tools@...il.com>
Subject: Re: perf_fuzzer compiled for x32 causes reboot

On Sun, 23 Feb 2014, H. Peter Anvin wrote:

> So we do a write to the buffer rather immediately before this happens,
> and in particular that will update the head:
> 
> 	rb->user_page->data_head = head;
> 
> However, that doesn't explain what is going on and in particular the
> write to whatever address was in %rbp.  The rest pretty much seems to be
> the page fault logic.

It turns out you don't even have to over-write rb->user_page->data_head.
Just touching the mmap page with a write of a single byte (it doesn't 
matter where) is enough to trigger the bug.

This is a pain to track down, it would be easier if I could get a 
replayable syscall trace, but even though the segfault is very 
reproducible with my fuzzer, it's very sensitive to extra syscalls in the 
trace path and the fuzzer logger/replayer path has a different number of 
write syscalls and won't trigger the problem.

> Incidentally, I doubt that this is x32-related in any way; there seems
> to be absolutely no difference between x86-64 perf and x32 perf; more
> likely it just makes the error more reproducible because the address
> space is so much smaller.

quite possibly.  I only began chasing the problem because when compiled 
for x32 this bug apparently will reboot the machine now and then (not just 
segfault the program).  I never saw that failure mode with x86_64, but 
again maybe it's just easier to hit with the reduced address space as you 
say.

Vince
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/