Re: disabling group leader perf_event

[Pekka Enberg <penberg@xxxxxxxxxx>]

2010/9/8 Paul Mackerras <paulus@xxxxxxxxx>:
>> 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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