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SubjectRe: [Patch v2 1/4] x86/speculation: Option to select app to app mitigation for spectre_v2

* 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)

?

> +
> + Not specifying this option is equivalent to
> + spectre_v2_app2app=auto.
> +
> spec_store_bypass_disable=
> [HW] Control Speculative Store Bypass (SSB) Disable mitigation
> (Speculative Store Bypass vulnerability)
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index fd2a8c1..c59a6c4 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -3,6 +3,7 @@
> #ifndef _ASM_X86_NOSPEC_BRANCH_H_
> #define _ASM_X86_NOSPEC_BRANCH_H_
>
> +#include <linux/static_key.h>
> #include <asm/alternative.h>
> #include <asm/alternative-asm.h>
> #include <asm/cpufeatures.h>
> @@ -217,6 +218,12 @@ enum spectre_v2_mitigation {
> SPECTRE_V2_IBRS_ENHANCED,
> };
>
> +enum spectre_v2_app2app_mitigation {
> + SPECTRE_V2_APP2APP_NONE,
> + SPECTRE_V2_APP2APP_LITE,
> + SPECTRE_V2_APP2APP_STRICT,
> +};
> +
> /* The Speculative Store Bypass disable variants */
> enum ssb_mitigation {
> SPEC_STORE_BYPASS_NONE,
> @@ -228,6 +235,8 @@ enum ssb_mitigation {
> extern char __indirect_thunk_start[];
> extern char __indirect_thunk_end[];
>
> +DECLARE_STATIC_KEY_FALSE(spectre_v2_app_lite);
> +
> /*
> * On VMEXIT we must ensure that no RSB predictions learned in the guest
> * can be followed in the host, by overwriting the RSB completely. Both
> diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
> index ee46dcb..c967012 100644
> --- a/arch/x86/kernel/cpu/bugs.c
> +++ b/arch/x86/kernel/cpu/bugs.c
> @@ -133,6 +133,12 @@ enum spectre_v2_mitigation_cmd {
> SPECTRE_V2_CMD_RETPOLINE_AMD,
> };
>
> +enum spectre_v2_app2app_mitigation_cmd {
> + SPECTRE_V2_APP2APP_CMD_AUTO,
> + SPECTRE_V2_APP2APP_CMD_LITE,
> + SPECTRE_V2_APP2APP_CMD_STRICT,
> +};
> +
> static const char *spectre_v2_strings[] = {
> [SPECTRE_V2_NONE] = "Vulnerable",
> [SPECTRE_V2_RETPOLINE_MINIMAL] = "Vulnerable: Minimal generic ASM retpoline",
> @@ -142,12 +148,24 @@ static const char *spectre_v2_strings[] = {
> [SPECTRE_V2_IBRS_ENHANCED] = "Mitigation: Enhanced IBRS",
> };
>
> +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?

> +
> #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?


> + * 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

Thanks,

Ingo

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