Commit 8a13906a authored by Jiri Kosina's avatar Jiri Kosina Committed by Greg Kroah-Hartman

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

commit 53c613fe 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.pmSigned-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent a436f6b2
......@@ -34,12 +34,10 @@ static void __init spectre_v2_select_mitigation(void);
static void __init ssb_select_mitigation(void);
static void __init l1tf_select_mitigation(void);
/*
* Our boot-time value of the SPEC_CTRL MSR. We read it once so that any
* writes to SPEC_CTRL contain whatever reserved bits have been set.
*/
u64 __ro_after_init x86_spec_ctrl_base;
/* The base value of the SPEC_CTRL MSR that always has to be preserved. */
u64 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
......@@ -322,6 +320,46 @@ static enum spectre_v2_mitigation_cmd __init spectre_v2_parse_cmdline(void)
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)
{
enum spectre_v2_mitigation_cmd cmd = spectre_v2_parse_cmdline();
......@@ -406,6 +444,9 @@ static void __init spectre_v2_select_mitigation(void)
setup_force_cpu_cap(X86_FEATURE_USE_IBRS_FW);
pr_info("Enabling Restricted Speculation for firmware calls\n");
}
/* Enable STIBP if appropriate */
arch_smt_update();
}
#undef pr_fmt
......@@ -798,6 +839,8 @@ static ssize_t l1tf_show_state(char *buf)
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
char *buf, unsigned int bug)
{
int ret;
if (!boot_cpu_has_bug(bug))
return sprintf(buf, "Not affected\n");
......@@ -812,10 +855,12 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
return sprintf(buf, "Mitigation: __user pointer sanitization\n");
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_IBRS_FW) ? ", IBRS_FW" : "",
(x86_spec_ctrl_base & SPEC_CTRL_STIBP) ? ", STIBP" : "",
spectre_v2_module_string());
return ret;
case X86_BUG_SPEC_STORE_BYPASS:
return sprintf(buf, "%s\n", ssb_strings[ssb_mode]);
......
......@@ -2045,6 +2045,12 @@ static void cpuhp_online_cpu_device(unsigned int cpu)
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)
{
int cpu, ret = 0;
......@@ -2071,8 +2077,10 @@ static int cpuhp_smt_disable(enum cpuhp_smt_control ctrlval)
*/
cpuhp_offline_cpu_device(cpu);
}
if (!ret)
if (!ret) {
cpu_smt_control = ctrlval;
arch_smt_update();
}
cpu_maps_update_done();
return ret;
}
......@@ -2083,6 +2091,7 @@ static int cpuhp_smt_enable(void)
cpu_maps_update_begin();
cpu_smt_control = CPU_SMT_ENABLED;
arch_smt_update();
for_each_present_cpu(cpu) {
/* Skip online CPUs and CPUs on offline nodes */
if (cpu_online(cpu) || !node_online(cpu_to_node(cpu)))
......
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