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

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Date:   Sat, 06 Jan 2018 17:32:46 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     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 11:49 +0000, David Woodhouse wrote:
> 
> +#if defined(CONFIG_X86_64) && defined(RETPOLINE)
> +/*
> + * Since the inline asm uses the %V modifier which is only in newer GCC,
> + * the 64-bit one is dependent on RETPOLINE not CONFIG_RETPOLINE.
> + */
> +# define NOSPEC_CALL ALTERNATIVE(                              \
> +       "call *%[thunk_target]\n",                              \
> +       "call __x86.indirect_thunk.%V[thunk_target]\n",         \
> +       X86_FEATURE_RETPOLINE)
> +# define THUNK_TARGET(addr) [thunk_target] "r" (addr)
> +#elif defined(CONFIG_X86_64) && defined(CONFIG_RETPOLINE)

                 ^^^^^^^^^^^^^ 

Arse. That'll invalidate my 32-bit test runs somewhat. I knew I should
have also repeated the "deliberately break the ASM and check it
crashes" tests. V6 coming in a little while, with 32-bit fixed
properly...

> +/*
> + * For i386 we use the original ret-equivalent retpoline, because
> + * otherwise we'll run out of registers. We don't care about CET
> + * here, anyway.
> + */
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