linux-kernel - Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app protection modes

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Message-ID: <nycvar.YFH.7.76.1811182358370.21108@cbobk.fhfr.pm>
Date:   Sun, 18 Nov 2018 23:59:52 +0100 (CET)
From:   Jiri Kosina <jikos@...nel.org>
To:     Tim Chen <tim.c.chen@...ux.intel.com>
cc:     Thomas Gleixner <tglx@...utronix.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 11/16] x86/speculation: Add Spectre v2 app to app
 protection modes

On Sat, 17 Nov 2018, Jiri Kosina wrote:

> > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> > index 81d1d5a..9c306e3 100644
> > --- a/Documentation/admin-guide/kernel-parameters.txt
> > +++ b/Documentation/admin-guide/kernel-parameters.txt
> > @@ -4215,6 +4215,26 @@
> >  			Not specifying this option is equivalent to
> >  			spectre_v2=auto.
> >  
> > +	spectre_v2_app2app=
> > +			[X86] Control mitigation of Spectre variant 2
> > +		        application to application (indirect branch speculation)
> > +			vulnerability.
> > +
> > +			off    - Unconditionally disable mitigations
> > +			lite   - Protect tasks which have requested restricted
> > +				 indirect branch speculation via the
> > +				 PR_SET_SPECULATION_CTRL prctl(). 
> 
> Don't we also want to do the same for SECCOMP processess, analogically how 
> we do it for SSBD?

IOW, how about patch below on top of your series? Thanks.


From: Jiri Kosina <jkosina@...e.cz>
Subject: [PATCH] x86/speculation: enforce STIBP for SECCOMP tasks in lite mode

If 'lite' mode of app2app protection from spectre_v2 is selected on
kernel command-line, we are currently applying STIBP protection to
non-dumpable tasks, and tasks that have explicitly requested such
protection via

	prctl(PR_SET_SPECULATION_CTRL, PR_SPEC_INDIR_BRANCH, PR_SPEC_ENABLE, 0, 0);

Let's extend this to cover also SECCOMP tasks (analogically to how we
apply SSBD protection).

Signed-off-by: Jiri Kosina <jkosina@...e.cz>
---
 Documentation/admin-guide/kernel-parameters.txt | 9 +++++----
 arch/x86/kernel/cpu/bugs.c                      | 2 ++
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 102f9a169eec..74f547e5c8f6 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4221,10 +4221,11 @@
 			vulnerability.
 
 			off    - Unconditionally disable mitigations
-			lite   - Protect tasks which are marked non-dumpable
-				 and tasks which have requested restricted
-				 indirect branch speculation via the
-				 PR_SET_SPECULATION_CTRL prctl(). 
+			lite   - Protect tasks which are marked non-dumpable,
+				 tasks which have requested restricted indirect
+				 branch speculation via the
+				 PR_SET_SPECULATION_CTRL prctl() and seccomp
+				 tasks.
 			strict - Protect all processes
 			auto   - Kernel selects the mode
 
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index e7f9334f18c0..3ec952108e87 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -863,6 +863,8 @@ void arch_seccomp_spec_mitigate(struct task_struct *task)
 {
 	if (ssb_mode == SPEC_STORE_BYPASS_SECCOMP)
 		ssb_prctl_set(task, PR_SPEC_FORCE_DISABLE);
+	if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_LITE)
+		set_task_stibp(task, true);
 }
 #endif
 

-- 
Jiri Kosina
SUSE Labs