linux-kernel - Re: [patch 22/24] x86/speculation: Create PRCTL interface to restrict indirect branch speculation

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Message-ID: <20181122071043.GA41788@gmail.com>
Date:   Thu, 22 Nov 2018 08:10:43 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Tom Lendacky <thomas.lendacky@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [patch 22/24] x86/speculation: Create PRCTL interface to
 restrict indirect branch speculation


* Thomas Gleixner <tglx@...utronix.de> wrote:

> From: Tim Chen <tim.c.chen@...ux.intel.com>
> 
> Add the PR_SPEC_INDIR_BRANCH option for the PR_GET_SPECULATION_CTRL and
> PR_SET_SPECULATION_CTRL prctls to allow fine grained per task control of
> indirect branch speculation via STIBP.
> 
> Invocations:
>  Check indirect branch speculation status with
>  - prctl(PR_GET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, 0, 0, 0);
> 
>  Enable indirect branch speculation with
>  - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);
> 
>  Disable indirect branch speculation with
>  - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_DISABLE, 0, 0);
> 
>  Force disable indirect branch speculation with
>  - prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_FORCE_DISABLE, 0, 0);
> 
> See Documentation/userspace-api/spec_ctrl.rst.
> 
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>

Please either de-capitalize the title to 'prctl()', or use PR_SPEC_PRCTL 
or PR_SET/GET_SPECULATION_CTRL - there's no such thing as 'PRCTL' 
interface - the interface is called prctl() and the speculation control 
ABIs have their own names.

This applies to the next patch as well.

> --- a/include/uapi/linux/prctl.h
> +++ b/include/uapi/linux/prctl.h
> @@ -212,6 +212,7 @@ struct prctl_mm_map {
>  #define PR_SET_SPECULATION_CTRL		53
>  /* Speculation control variants */
>  # define PR_SPEC_STORE_BYPASS		0
> +# define PR_SPEC_INDIR_BRANCH		1
>  /* Return and control values for PR_SET/GET_SPECULATION_CTRL */
>  # define PR_SPEC_NOT_AFFECTED		0
>  # define PR_SPEC_PRCTL			(1UL << 0)
> --- a/tools/include/uapi/linux/prctl.h
> +++ b/tools/include/uapi/linux/prctl.h
> @@ -212,6 +212,7 @@ struct prctl_mm_map {
>  #define PR_SET_SPECULATION_CTRL		53
>  /* Speculation control variants */
>  # define PR_SPEC_STORE_BYPASS		0
> +# define PR_SPEC_INDIR_BRANCH		1
>  /* Return and control values for PR_SET/GET_SPECULATION_CTRL */
>  # define PR_SPEC_NOT_AFFECTED		0
>  # define PR_SPEC_PRCTL			(1UL << 0)

Please de-abbreviate the new ABI: PR_SPEC_INDIRECT_BRANCH?

Thanks,

	Ingo