linux-kernel - Re: [PATCH 07/12] perf_events: add LBR software filter support for Intel X86

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Date:	Thu, 06 Oct 2011 18:43:44 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Stephane Eranian <eranian@...gle.com>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, acme@...hat.com,
	ming.m.lin@...el.com, robert.richter@....com, ravitillo@....gov,
	"masami.hiramatsu.pt" <masami.hiramatsu.pt@...achi.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH 07/12] perf_events: add LBR software filter support for
 Intel X86

On Thu, 2011-10-06 at 17:32 +0200, Andi Kleen wrote:
> > +	kernel_insn_init(&insn, kaddr);
> > +	insn_get_opcode(&insn);
> 
> This makes me uncomfortable. AFAIK that's the first use of the opcode
> decoder being used directly for user space. It has a quite large attack
> surface. Who says it cannot be exploited?

You mean:
arch/x86/kernel/cpu/perf_event_intel_ds.c:intel_pmu_pebs_fixup_ip()
doesn't use the opcode decoder on user space code?

ISTR Masami telling me they ran fuzzers on it, feeding it bad
instructions etc. But maybe he can tell more.
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