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SubjectRe: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels
On Mon, Feb 5, 2018 at 4:30 PM, Ingo Molnar <mingo@kernel.org> wrote:
>
> * Andy Lutomirski <luto@amacapital.net> wrote:
>
>>
>>
>> > 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.
>
> AFAICS there's various entry paths where it's not used I think: for example the
> compat system calls in entry_64_compat.S don't seem to encode RBP in such a
> fashion (unless I missed some macro side effect).

Then that's a separate bug that should be fixed. Josh?

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