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SubjectRe: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels
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> On Feb 5, 2018, at 3:42 AM, Ingo Molnar <mingo@kernel.org> wrote:
>
>
> * Dan Williams <dan.j.williams@intel.com> 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.

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