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SubjectRe: [Patch v2 1/4] x86/speculation: Option to select app to app mitigation for spectre_v2
Date
On 10/02/2018 02:23 AM, Ingo Molnar wrote:
>
> * Tim Chen <tim.c.chen@linux.intel.com> wrote:
>
>> Subject: x86/speculation: Option to select app to app mitigation for spectre_v2
>>
>
> We prefer to start commit titles with verbs, not nouns, so this should be something like:
>
> x86/speculation: Add option to select app to app mitigation for spectre_v2
>
>> Jiri Kosina's patch makes IBPB and STIBP available for
>> general spectre v2 app to app mitigation. IBPB will be issued for
>> switching to an app that's not ptraceable by the previous
>> app and STIBP will be always turned on.
>>
>> However, app to app exploit is in general difficult
>> due to address space layout randomization in apps and
>> the need to know an app's address space layout ahead of time.
>> Users may not wish to incur app to app performance
>> overhead from IBPB and STIBP for general non security sensitive apps.
>>
>> This patch provides a lite option for spectre_v2 app to app
>> mitigation where IBPB is only issued for security sensitive
>> non-dumpable app.
>>
>> The strict option will keep system at high security level
>> where IBPB and STIBP are used to defend all apps against
>> spectre_v2 app to app attack.
>
> s/system
> /the system
>
> s/attack
> attacks
>
>> + spectre_v2_app2app=
>> + [X86] Control app to app mitigation of Spectre variant 2
>> + (indirect branch speculation) vulnerability.
>> +
>> + lite - only turn on mitigation for non-dumpable processes
>> + strict - protect against attacks for all user processes
>> + auto - let kernel decide lite or strict mode
>
> Perhaps add:
> lite - only turn on mitigation for non-dumpable processes (i.e.
> protect daemons and other privileged processes that tend
> to be non-dumpable)
>
> ?

Will do.

>
>> +

>>
>> +static const char *spectre_v2_app2app_strings[] = {
>> + [SPECTRE_V2_APP2APP_NONE] = "App-App Vulnerable",
>> + [SPECTRE_V2_APP2APP_LITE] = "App-App Mitigation: Protect only non-dumpable process",
>> + [SPECTRE_V2_APP2APP_STRICT] = "App-App Mitigation: Full app to app attack protection",
>> +};
>> +
>> +DEFINE_STATIC_KEY_FALSE(spectre_v2_app_lite);
>> +EXPORT_SYMBOL(spectre_v2_app_lite);
>
> EXPORT_SYMBOL_GPL() I suspect?

This is only used in the core kernel functions related to
context switches. So I don't expect any module functions
needing this value.

>
>> +
>> #undef pr_fmt
>> #define pr_fmt(fmt) "Spectre V2 : " fmt
>>
>> static enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init =
>> SPECTRE_V2_NONE;
>>
>> +static enum spectre_v2_mitigation spectre_v2_app2app_enabled __ro_after_init =
>> + SPECTRE_V2_APP2APP_NONE;
>> +
>> void
>> x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
>> {
>> @@ -275,6 +293,46 @@ static const struct {
>> { "auto", SPECTRE_V2_CMD_AUTO, false },
>> };
>>
>> +static const struct {
>> + const char *option;
>> + enum spectre_v2_app2app_mitigation_cmd cmd;
>> + bool secure;
>> +} app2app_mitigation_options[] = {
>> + { "lite", SPECTRE_V2_APP2APP_CMD_LITE, false },
>> + { "strict", SPECTRE_V2_APP2APP_CMD_STRICT, false },
>> + { "auto", SPECTRE_V2_APP2APP_CMD_AUTO, false },
>> +};
>
> Am I reading this right that it's not possible to configure this to 'none', i.e. to disable the
> protection altogether?

Sure, I can add a none option. I'll probably put that in patch 4
which is easy to disable the mitigation by not turning on
STIBP flag for the none option.

>
>
>> + * For lite protection mode, we only protect the non-dumpable
>> + * processes.
>> + *
>> + * Otherwise check if the current (previous) task has access to the memory
>> + * of the @tsk (next) task for strict app to app protection.
>> + * If access is denied, make sure to
>> * issue a IBPB to stop user->user Spectre-v2 attacks.
>
> s/a IBPB
> /an IBPB
>

Tim

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