linux-kernel - Re: [PATCH v5 02/12] x86/retpoline: Add initial retpoline support

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Date:   Sat, 06 Jan 2018 19:17:53 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Eric Biggers <ebiggers3@...il.com>
Cc:     Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>, tglx@...utronix.de,
        Kees Cook <keescook@...gle.com>,
        Rik van Riel <riel@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH v5 02/12] x86/retpoline: Add initial retpoline support

On Sat, 2018-01-06 at 10:35 -0800, Eric Biggers wrote:
> On Sat, Jan 06, 2018 at 11:49:24AM +0000, David Woodhouse wrote:
> > 
> > +/*
> > + * NOSPEC_JMP and NOSPEC_CALL macros can be used instead of a simple
> > + * indirect jmp/call which may be susceptible to the Spectre variant 2
> > + * attack.
> > + */
>
> Can be, or must be?

Can be is fine. It isn't necessarily the case that all indirect
branches MUST be changed. Although we *have* been auditing the kernel
binary and looking for them, some of them can stay as they are.


> Would it make any sense to name these INDIRECT_JMP and INDIRECT_CALL instead?
> NOSPEC_ seems to describe how it needs to be implemented on some CPUs, as
> opposed to what the user wants to do (make an indirect jump or call).

While NOSPEC_CALL explains why you're using the macro instead of just
'call'. I think this is fine. I'd rather not do too much bikeshedding
over the names.
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