linux-kernel - Re: [Patch v7 14/18] x86/speculation: Add 'seccomp' Spectre v2 app to app protection mode

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Date:   Wed, 21 Nov 2018 10:16:40 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        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>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        stable@...r.kernel.org, Jiri Kosina <jkosina@...e.cz>
Subject: Re: [Patch v7 14/18] x86/speculation: Add 'seccomp' Spectre v2 app to
 app protection mode

On 11/21/2018 05:52 AM, Thomas Gleixner wrote:
> On Tue, 20 Nov 2018, Tim Chen wrote:
>> According to software guidance:
>>
>> "Setting ... STIBP ... on a logical processor prevents the predicted
>> targets of indirect branches on any logical processor of that core
>> from being controlled by software that executes (or executed
>> previously) on another logical processor of the same core."
>>
>> https://software.intel.com/security-software-guidance/insights/deep-dive-single-thread-indirect-branch-predictors
>>
>> Hence setting STIBP on a sandboxed task will prevent the task
>> from attacking other sibling threads or getting attacked.
> 
> That's not sufficient, because you need an IBPB when the sandboxed task is
> switched out.
> 

Right.  Which means this change is also needed:

Tim

diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
index 616694c..de31438 100644
--- a/arch/x86/mm/tlb.c
+++ b/arch/x86/mm/tlb.c
@@ -202,7 +202,8 @@ static bool ibpb_needed(struct task_struct *tsk, u64 last_ctx_id)
 	 */
 
 	if (static_branch_unlikely(&spectre_v2_app_lite))
-		return test_tsk_thread_flag(tsk, TIF_SPEC_INDIR_BRANCH);
+		return test_tsk_thread_flag(tsk, TIF_SPEC_INDIR_BRANCH) ||
+		       test_tsk_thread_flag(current, TIF_SPEC_INDIR_BRANCH);
 	else
 		return ptrace_may_access_sched(tsk, PTRACE_MODE_SPEC_IBPB);
 }