linux-kernel - Re: [Patch v3 12/13] x86/speculation: Protect non-dumpable processes against Spectre v2 attack

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Message-ID: <6fdbb79e-a9a9-7d59-5d43-23e8f66a279c@linux.intel.com>
Date:   Fri, 26 Oct 2018 11:10:20 -0700
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Waiman Long <longman9394@...il.com>,
        Jiri Kosina <jikos@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     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>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [Patch v3 12/13] x86/speculation: Protect non-dumpable processes
 against Spectre v2 attack

On 10/26/2018 10:46 AM, Waiman Long wrote:
> On 10/17/2018 01:59 PM, Tim Chen wrote:
>> Mark the non-dumpable processes with TIF_STIBP flag so they will
>> use STIBP and IBPB defenses against Spectre v2 attack from
>> processes in user space.
>>
>> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
>> ---
>>  arch/x86/kernel/cpu/bugs.c | 21 +++++++++++++++++++++
>>  1 file changed, 21 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
>> index 1d317f2..cc77b9e 100644
>> --- a/arch/x86/kernel/cpu/bugs.c
>> +++ b/arch/x86/kernel/cpu/bugs.c
>> @@ -14,6 +14,7 @@
>>  #include <linux/module.h>
>>  #include <linux/nospec.h>
>>  #include <linux/prctl.h>
>> +#include <linux/sched/coredump.h>
>>  
>>  #include <asm/spec-ctrl.h>
>>  #include <asm/cmdline.h>
>> @@ -773,6 +774,26 @@ int arch_prctl_spec_ctrl_set(struct task_struct *task, unsigned long which,
>>  	}
>>  }
>>  
>> +void arch_set_dumpable(struct task_struct *tsk, unsigned int value)
>> +{
>> +	bool update;
>> +
>> +	if (!static_branch_unlikely(&spectre_v2_app_lite))
>> +		return;
>> +	if (!static_cpu_has(X86_FEATURE_STIBP))
>> +		return;
>> +	if (spectre_v2_app2app_enabled == SPECTRE_V2_APP2APP_NONE)
>> +		return;
> 
> The third if above seems to be a subset of the first one. Do you need to
> do the check one more time?
> 

Yes, it is redundant and can be removed.

Tim