Re: disabling group leader perf_event

From: Pekka Enberg <penberg@kernel.org>
To: Paul Mackerras <paulus@samba.org>
Cc: "Ingo Molnar" <mingo@elte.hu>, "Avi Kivity" <avi@redhat.com>,
	"Pekka Enberg" <penberg@cs.helsinki.fi>,
	"Tom Zanussi" <tzanussi@gmail.com>,
	"Frédéric Weisbecker" <fweisbec@gmail.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Arnaldo Carvalho de Melo" <acme@redhat.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	linux-perf-users@vger.kernel.org,
	linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: disabling group leader perf_event
Date: Wed, 8 Sep 2010 09:16:49 +0300	[thread overview]
Message-ID: <AANLkTi=YdAxdGv1nEEZ4w0jM0K3ss0g5x7_5cU8xNEhj@mail.gmail.com> (raw)
In-Reply-To: <20100908014409.GA17010@brick.ozlabs.ibm.com>

2010/9/8 Paul Mackerras <paulus@samba.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