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

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Message-Id: <6CCF65EF-325A-4207-9C5E-2CD2D8E2A7E4@amacapital.net>
Date:   Mon, 5 Feb 2018 07:37:40 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Dan Williams <dan.j.williams@...el.com>, tglx@...utronix.de,
        Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
        luto@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        torvalds@...ux-foundation.org
Subject: Re: [PATCH v2 1/3] x86/entry: Clear extra registers beyond syscall arguments for 64bit kernels



> On Feb 5, 2018, at 3:42 AM, Ingo Molnar <mingo@...nel.org> wrote:
> 
> 
> * Dan Williams <dan.j.williams@...el.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.