From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Thu, 8 Apr 2010 12:05:50 +0000 (+0200)
Subject: perf: Fix unsafe frame rewinding with hot regs fetching
X-Git-Tag: v2.6.34-rc6~84^2
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=ab285f2b5290d92b7ec1a6f9aad54308dadf6157;p=pandora-kernel.git

perf: Fix unsafe frame rewinding with hot regs fetching

When we fetch the hot regs and rewind to the nth caller, it
might happen that we dereference a frame pointer outside the
kernel stack boundaries, like in this example:

	perf_trace_sched_switch+0xd5/0x120
        schedule+0x6b5/0x860
        retint_careful+0xd/0x21

Since we directly dereference a userspace frame pointer here while
rewinding behind retint_careful, this may end up in a crash.

Fix this by simply using probe_kernel_address() when we rewind the
frame pointer.

This issue will have a much more proper fix in the next version of the
perf_arch_fetch_caller_regs() API that will only need to rewind to the
first caller.

Reported-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: David Miller <davem@davemloft.net>
Cc: Archs <linux-arch@vger.kernel.org>
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