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

From: Ingo Molnar <mingo@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
	x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
	Andy Lutomirski <luto@kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jiri Kosina <jkosina@suse.cz>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Andi Kleen <ak@linux.intel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Casey Schaufler <casey.schaufler@intel.com>,
	Asit Mallick <asit.k.mallick@intel.com>,
	Arjan van de Ven <arjan@linux.intel.com>,
	Jon Masters <jcm@redhat.com>, Waiman Long <longman9394@gmail.com>,
	Greg KH <gregkh@linuxfoundation.org>,
	Dave Stewart <david.c.stewart@intel.com>,
	Kees Cook <keescook@chromium.org>,
	Tim Chen <tim.c.chen@linux.intel.com>
Subject: Re: [patch 22/24] x86/speculation: Create PRCTL interface to restrict indirect branch speculation
Date: Thu, 22 Nov 2018 08:10:43 +0100	[thread overview]
Message-ID: <20181122071043.GA41788@gmail.com> (raw)
In-Reply-To: <20181121201724.414692525@linutronix.de>

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

> From: Tim Chen <tim.c.chen@linux.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@linux.intel.com>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.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