linux-kernel - Re: disabling group leader perf

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Date:	Wed, 8 Sep 2010 09:16:49 +0300
From:	Pekka Enberg <penberg@...nel.org>
To:	Paul Mackerras <paulus@...ba.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Avi Kivity <avi@...hat.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Tom Zanussi <tzanussi@...il.com>,
	Frédéric Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-perf-users@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: disabling group leader perf_event

2010/9/8 Paul Mackerras <paulus@...ba.org>:
>> We start with trivial (and useless) special case of something like:
>>
>> #define MAX_BYTECODE_SIZE 256
>>
>> int x86_bytecode_verify(char *opcodes, unsigned int len)
>> {
>>
>>       if (len-1 > MAX_BYTECODE_SIZE-1)
>>               return -EINVAL;
>>
>>       if (opcodes[0] != 0xc3) /* RET instruction */
>>               return -EINVAL;
>>
>>       return 0;
>> }
>>
>> ... and then we add checks for accepted/safe x86 patterns of
>> instructions step by step - always keeping it 100% correct.
>
> So... I would be interested to see you add the case for the MOV
> instruction. :)

Heh, which one of them - there are tons of variants under 'mov' on
x86? On a more serious note: the biggest problem is that you need to
do verification during execution because you don't know the exact
address until then for most addressing modes that use registers.

                        Pekka
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