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

[Tim Chen]

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@xxxxxxxxxxxxxxx>
>> ---
>>  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