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x86/vmscape: Enable the mitigation

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Commit 556c1ad666 upstream.

Enable the previously added mitigation for VMscape. Add the cmdline
vmscape={off|ibpb|force} and sysfs reporting.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Pawan Gupta 2025-08-14 10:20:42 -07:00 committed by Greg Kroah-Hartman
parent 15006289e5
commit 893387c186
6 changed files with 106 additions and 0 deletions
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1
Documentation/ABI/testing/sysfs-devices-system-cpu
View File

@ -528,6 +528,7 @@ What: /sys/devices/system/cpu/vulnerabilities
/sys/devices/system/cpu/vulnerabilities/srbds
/sys/devices/system/cpu/vulnerabilities/tsa
/sys/devices/system/cpu/vulnerabilities/tsx_async_abort
/sys/devices/system/cpu/vulnerabilities/vmscape
Date: January 2018
Contact: Linux kernel mailing list <linux-kernel@vger.kernel.org>
Description: Information about CPU vulnerabilities

11
Documentation/admin-guide/kernel-parameters.txt
View File

@ -3297,6 +3297,7 @@
srbds=off [X86,INTEL]
ssbd=force-off [ARM64]
tsx_async_abort=off [X86]
vmscape=off [X86]
Exceptions:
This does not have any effect on
@ -6813,6 +6814,16 @@
vmpoff= [KNL,S390] Perform z/VM CP command after power off.
Format: <command>
vmscape= [X86] Controls mitigation for VMscape attacks.
VMscape attacks can leak information from a userspace
hypervisor to a guest via speculative side-channels.
off - disable the mitigation
ibpb - use Indirect Branch Prediction Barrier
(IBPB) mitigation (default)
force - force vulnerability detection even on
unaffected processors
vsyscall= [X86-64]
Controls the behavior of vsyscalls (i.e. calls to
fixed addresses of 0xffffffffff600x00 from legacy

9
arch/x86/Kconfig
View File

@ -2595,6 +2595,15 @@ config MITIGATION_TSA
security vulnerability on AMD CPUs which can lead to forwarding of
invalid info to subsequent instructions and thus can affect their
timing and thereby cause a leakage.
config MITIGATION_VMSCAPE
bool "Mitigate VMSCAPE"
depends on KVM
default y
help
Enable mitigation for VMSCAPE attacks. VMSCAPE is a hardware security
vulnerability on Intel and AMD CPUs that may allow a guest to do
Spectre v2 style attacks on userspace hypervisor.
endif
config ARCH_HAS_ADD_PAGES

77
arch/x86/kernel/cpu/bugs.c
View File

@ -50,6 +50,7 @@ static void __init gds_select_mitigation(void);
static void __init srso_select_mitigation(void);
static void __init its_select_mitigation(void);
static void __init tsa_select_mitigation(void);
static void __init vmscape_select_mitigation(void);
/* The base value of the SPEC_CTRL MSR without task-specific bits set */
u64 x86_spec_ctrl_base;
@ -193,6 +194,7 @@ void __init cpu_select_mitigations(void)
gds_select_mitigation();
its_select_mitigation();
tsa_select_mitigation();
vmscape_select_mitigation();
}
/*
@ -2898,6 +2900,68 @@ pred_cmd:
x86_pred_cmd = PRED_CMD_SBPB;
}
#undef pr_fmt
#define pr_fmt(fmt) "VMSCAPE: " fmt
enum vmscape_mitigations {
VMSCAPE_MITIGATION_NONE,
VMSCAPE_MITIGATION_AUTO,
VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER,
VMSCAPE_MITIGATION_IBPB_ON_VMEXIT,
};
static const char * const vmscape_strings[] = {
[VMSCAPE_MITIGATION_NONE] = "Vulnerable",
/* [VMSCAPE_MITIGATION_AUTO] */
[VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER] = "Mitigation: IBPB before exit to userspace",
[VMSCAPE_MITIGATION_IBPB_ON_VMEXIT] = "Mitigation: IBPB on VMEXIT",
};
static enum vmscape_mitigations vmscape_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_VMSCAPE) ? VMSCAPE_MITIGATION_AUTO : VMSCAPE_MITIGATION_NONE;
static int __init vmscape_parse_cmdline(char *str)
{
if (!str)
return -EINVAL;
if (!strcmp(str, "off")) {
vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
} else if (!strcmp(str, "ibpb")) {
vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
} else if (!strcmp(str, "force")) {
setup_force_cpu_bug(X86_BUG_VMSCAPE);
vmscape_mitigation = VMSCAPE_MITIGATION_AUTO;
} else {
pr_err("Ignoring unknown vmscape=%s option.\n", str);
}
return 0;
}
early_param("vmscape", vmscape_parse_cmdline);
static void __init vmscape_select_mitigation(void)
{
if (cpu_mitigations_off() ||
!boot_cpu_has_bug(X86_BUG_VMSCAPE) ||
!boot_cpu_has(X86_FEATURE_IBPB)) {
vmscape_mitigation = VMSCAPE_MITIGATION_NONE;
return;
}
if (vmscape_mitigation == VMSCAPE_MITIGATION_AUTO)
vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER;
if (retbleed_mitigation == RETBLEED_MITIGATION_IBPB ||
srso_mitigation == SRSO_MITIGATION_IBPB_ON_VMEXIT)
vmscape_mitigation = VMSCAPE_MITIGATION_IBPB_ON_VMEXIT;
if (vmscape_mitigation == VMSCAPE_MITIGATION_IBPB_EXIT_TO_USER)
setup_force_cpu_cap(X86_FEATURE_IBPB_EXIT_TO_USER);
pr_info("%s\n", vmscape_strings[vmscape_mitigation]);
}
#undef pr_fmt
#define pr_fmt(fmt) fmt
@ -3146,6 +3210,11 @@ static ssize_t tsa_show_state(char *buf)
return sysfs_emit(buf, "%s\n", tsa_strings[tsa_mitigation]);
}
static ssize_t vmscape_show_state(char *buf)
{
return sysfs_emit(buf, "%s\n", vmscape_strings[vmscape_mitigation]);
}
static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr,
char *buf, unsigned int bug)
{
@ -3210,6 +3279,9 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
case X86_BUG_TSA:
return tsa_show_state(buf);
case X86_BUG_VMSCAPE:
return vmscape_show_state(buf);
default:
break;
}
@ -3299,4 +3371,9 @@ ssize_t cpu_show_tsa(struct device *dev, struct device_attribute *attr, char *bu
{
return cpu_show_common(dev, attr, buf, X86_BUG_TSA);
}
ssize_t cpu_show_vmscape(struct device *dev, struct device_attribute *attr, char *buf)
{
return cpu_show_common(dev, attr, buf, X86_BUG_VMSCAPE);
}
#endif

7
drivers/base/cpu.c
View File

@ -606,6 +606,11 @@ ssize_t __weak cpu_show_tsa(struct device *dev, struct device_attribute *attr, c
return sysfs_emit(buf, "Not affected\n");
}
ssize_t __weak cpu_show_vmscape(struct device *dev, struct device_attribute *attr, char *buf)
{
return sysfs_emit(buf, "Not affected\n");
}
static DEVICE_ATTR(meltdown, 0444, cpu_show_meltdown, NULL);
static DEVICE_ATTR(spectre_v1, 0444, cpu_show_spectre_v1, NULL);
static DEVICE_ATTR(spectre_v2, 0444, cpu_show_spectre_v2, NULL);
@ -622,6 +627,7 @@ static DEVICE_ATTR(spec_rstack_overflow, 0444, cpu_show_spec_rstack_overflow, NU
static DEVICE_ATTR(reg_file_data_sampling, 0444, cpu_show_reg_file_data_sampling, NULL);
static DEVICE_ATTR(indirect_target_selection, 0444, cpu_show_indirect_target_selection, NULL);
static DEVICE_ATTR(tsa, 0444, cpu_show_tsa, NULL);
static DEVICE_ATTR(vmscape, 0444, cpu_show_vmscape, NULL);
static struct attribute *cpu_root_vulnerabilities_attrs[] = {
&dev_attr_meltdown.attr,
@ -640,6 +646,7 @@ static struct attribute *cpu_root_vulnerabilities_attrs[] = {
&dev_attr_reg_file_data_sampling.attr,
&dev_attr_indirect_target_selection.attr,
&dev_attr_tsa.attr,
&dev_attr_vmscape.attr,
NULL
};

1
include/linux/cpu.h
View File

@ -79,6 +79,7 @@ extern ssize_t cpu_show_reg_file_data_sampling(struct device *dev,
extern ssize_t cpu_show_indirect_target_selection(struct device *dev,
struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_tsa(struct device *dev, struct device_attribute *attr, char *buf);
extern ssize_t cpu_show_vmscape(struct device *dev, struct device_attribute *attr, char *buf);
extern __printf(4, 5)
struct device *cpu_device_create(struct device *parent, void *drvdata,