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Commit 233b9d7d authored by Jiri Kosina's avatar Jiri Kosina Committed by Greg Kroah-Hartman
Browse files

x86/speculation: Enable cross-hyperthread spectre v2 STIBP mitigation 



commit 53c613fe6349994f023245519265999eed75957f upstream.

STIBP is a feature provided by certain Intel ucodes / CPUs. This feature
(once enabled) prevents cross-hyperthread control of decisions made by
indirect branch predictors.

Enable this feature if

- the CPU is vulnerable to spectre v2
- the CPU supports SMT and has SMT siblings online
- spectre_v2 mitigation autoselection is enabled (default)

After some previous discussion, this leaves STIBP on all the time, as wrmsr
on crossing kernel boundary is a no-no. This could perhaps later be a bit
more optimized (like disabling it in NOHZ, experiment with disabling it in
idle, etc) if needed.

Note that the synchronization of the mask manipulation via newly added
spec_ctrl_mutex is currently not strictly needed, as the only updater is
already being serialized by cpu_add_remove_lock, but let's make this a
little bit more future-proof.

Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc:  "WoodhouseDavid" <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc:  "SchauflerCasey" <casey.schaufler@intel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/nycvar.YFH.7.76.1809251438240.15880@cbobk.fhfr.pm


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1e3430e2

arch/x86/kernel/cpu/bugs.c

+51 −6
Original line number Original line Diff line number Diff line
@@ -35,12 +35,10 @@ static void __init spectre_v2_select_mitigation(void); 
static void __init ssb_select_mitigation(void);

static void __init ssb_select_mitigation(void);

static void __init l1tf_select_mitigation(void);

static void __init l1tf_select_mitigation(void);





/*

/* The base value of the SPEC_CTRL MSR that always has to be preserved. */

 * Our boot-time value of the SPEC_CTRL MSR. We read it once so that any

u64 x86_spec_ctrl_base;

 * writes to SPEC_CTRL contain whatever reserved bits have been set.

 */

u64 __ro_after_init x86_spec_ctrl_base;

EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);

EXPORT_SYMBOL_GPL(x86_spec_ctrl_base);

static DEFINE_MUTEX(spec_ctrl_mutex);





/*

/*

 * The vendor and possibly platform specific bits which can be modified in

 * The vendor and possibly platform specific bits which can be modified in
@@ -325,6 +323,46 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void) 
	return cmd;

	return cmd;

}

}





static bool stibp_needed(void)

{

	if (spectre_v2_enabled == SPECTRE_V2_NONE)

		return false;



	if (!boot_cpu_has(X86_FEATURE_STIBP))

		return false;



	return true;

}



static void update_stibp_msr(void *info)

{

	wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);

}



void arch_smt_update(void)

{

	u64 mask;



	if (!stibp_needed())

		return;



	mutex_lock(&spec_ctrl_mutex);

	mask = x86_spec_ctrl_base;

	if (cpu_smt_control == CPU_SMT_ENABLED)

		mask |= SPEC_CTRL_STIBP;

	else

		mask &= ~SPEC_CTRL_STIBP;



	if (mask != x86_spec_ctrl_base) {

		pr_info("Spectre v2 cross-process SMT mitigation: %s STIBP\n",

				cpu_smt_control == CPU_SMT_ENABLED ?

				"Enabling" : "Disabling");

		x86_spec_ctrl_base = mask;

		on_each_cpu(update_stibp_msr, NULL, 1);

	}

	mutex_unlock(&spec_ctrl_mutex);

}



static void __init spectre_v2_select_mitigation(void)

static void __init spectre_v2_select_mitigation(void)

{

{

	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();

	enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
@@ -424,6 +462,9 @@ static void __init spectre_v2_select_mitigation(void) 
		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);

		setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);

		pr_info("Enabling Restricted Speculation for firmware calls\n");

		pr_info("Enabling Restricted Speculation for firmware calls\n");

	}

	}



	/* Enable STIBP if appropriate */

	arch_smt_update();

}

}





#undef pr_fmt

#undef pr_fmt
@@ -814,6 +855,8 @@ static ssize_t l1tf_show_state(char *buf) 
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,

static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,

			       char *buf, unsigned int bug)

			       char *buf, unsigned int bug)

{

{

	int ret;



	if (!boot_cpu_has_bug(bug))

	if (!boot_cpu_has_bug(bug))

		return sprintf(buf, "Not affected\n");

		return sprintf(buf, "Not affected\n");
@@ -831,10 +874,12 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr 
		return sprintf(buf, "Mitigation: __user pointer sanitization\n");

		return sprintf(buf, "Mitigation: __user pointer sanitization\n");





	case X86_BUG_SPECTRE_V2:

	case X86_BUG_SPECTRE_V2:

		return sprintf(buf, "%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],

		ret = sprintf(buf, "%s%s%s%s%s\n", spectre_v2_strings[spectre_v2_enabled],

			       boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",

			       boot_cpu_has(X86_FEATURE_USE_IBPB) ? ", IBPB" : "",

			       boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",

			       boot_cpu_has(X86_FEATURE_USE_IBRS_FW) ? ", IBRS_FW" : "",

			       (x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",

			       spectre_v2_module_string());

			       spectre_v2_module_string());

		return ret;





	case X86_BUG_SPEC_STORE_BYPASS:

	case X86_BUG_SPEC_STORE_BYPASS:

		return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);

		return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);

kernel/cpu.c

+10 −1
Original line number Original line Diff line number Diff line
@@ -2026,6 +2026,12 @@ static void cpuhp_online_cpu_device(unsigned int cpu) 
	kobject_uevent(&dev->kobj, KOBJ_ONLINE);

	kobject_uevent(&dev->kobj, KOBJ_ONLINE);

}

}





/*

 * Architectures that need SMT-specific errata handling during SMT hotplug

 * should override this.

 */

void __weak arch_smt_update(void) { };



static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)

static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)

{

{

	int cpu, ret = 0;

	int cpu, ret = 0;
@@ -2052,8 +2058,10 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval) 
		 */

		 */

		cpuhp_offline_cpu_device(cpu);

		cpuhp_offline_cpu_device(cpu);

	}

	}

	if (!ret)

	if (!ret) {

		cpu_smt_control = ctrlval;

		cpu_smt_control = ctrlval;

		arch_smt_update();

	}

	cpu_maps_update_done();

	cpu_maps_update_done();

	return ret;

	return ret;

}

}
@@ -2064,6 +2072,7 @@ static int cpuhp_smt_enable(void) 




	cpu_maps_update_begin();

	cpu_maps_update_begin();

	cpu_smt_control = CPU_SMT_ENABLED;

	cpu_smt_control = CPU_SMT_ENABLED;

	arch_smt_update();

	for_each_present_cpu(cpu) {

	for_each_present_cpu(cpu) {

		/* Skip online CPUs and CPUs on offline nodes */

		/* Skip online CPUs and CPUs on offline nodes */

		if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))

		if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))