Re: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels

[Andy Lutomirski]

> On Feb 5, 2018, at 3:42 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
> 
> 
> * Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> 
>> +    /*
>> +     * Sanitize extra registers of values that a speculation attack
>> +     * might want to exploit. In the CONFIG_FRAME_POINTER=y case,
>> +     * the expectation is that %ebp will be clobbered before it
>> +     * could be used.
>> +     */
>> +    .macro CLEAR_EXTRA_REGS_NOSPEC
>> +    xorq %r15, %r15
>> +    xorq %r14, %r14
>> +    xorq %r13, %r13
>> +    xorq %r12, %r12
>> +    xorl %ebx, %ebx
>> +#ifndef CONFIG_FRAME_POINTER
>> +    xorl %ebp, %ebp
>> +#endif
>> +    .endm
> 
> Yeah, so this series look pretty good to me, but there's one small detail: I think 
> RBP should be cleared unconditionally here, even in the CONFIG_FRAME_POINTERS=y 
> case, because:

ENCODE_FRAME_POINTER should take care of rbp, though.