Opportunistically initialize IA32_FEAT_CTL to enable VMX when the MSR is left unlocked by BIOS. Configuring feature control at boot time paves the way for similar enabling of other features, e.g. Software Guard Extensions (SGX).
Temporarily leave equivalent KVM code in place in order to avoid introducing a regression on Centaur and Zhaoxin CPUs, e.g. removing KVM's code would leave the MSR unlocked on those CPUs and would break existing functionality if people are loading kvm_intel on Centaur and/or Zhaoxin. Defer enablement of the boot-time configuration on Centaur and Zhaoxin to future patches to aid bisection.
Note, Local Machine Check Exceptions (LMCE) are also supported by the kernel and enabled via feature control, but the kernel currently uses LMCE if and and only if the feature is explicitly enabled by BIOS. Keep the current behavior to avoid introducing bugs, future patches can opt in to opportunistic enabling if it's deemed desirable to do so.
Always lock IA32_FEAT_CTL if it exists, even if the CPU doesn't support VMX, so that other existing and future kernel code that queries the MSR can assume it's locked.
Start from a clean slate when constructing the value to write to IA32_FEAT_CTL, i.e. ignore whatever value BIOS left in the MSR so as not to enable random features or fault on the WRMSR.
Suggested-by: Borislav Petkov bp@suse.de Cc: Jarkko Sakkinen jarkko.sakkinen@linux.intel.com Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com --- arch/x86/Kconfig.cpu | 4 ++++ arch/x86/kernel/cpu/Makefile | 1 + arch/x86/kernel/cpu/cpu.h | 4 ++++ arch/x86/kernel/cpu/feat_ctl.c | 37 ++++++++++++++++++++++++++++++++++ arch/x86/kernel/cpu/intel.c | 2 ++ 5 files changed, 48 insertions(+) create mode 100644 arch/x86/kernel/cpu/feat_ctl.c
diff --git a/arch/x86/Kconfig.cpu b/arch/x86/Kconfig.cpu index af9c967782f6..98be76fa2978 100644 --- a/arch/x86/Kconfig.cpu +++ b/arch/x86/Kconfig.cpu @@ -387,6 +387,10 @@ config X86_DEBUGCTLMSR def_bool y depends on !(MK6 || MWINCHIPC6 || MWINCHIP3D || MCYRIXIII || M586MMX || M586TSC || M586 || M486SX || M486) && !UML
+config IA32_FEAT_CTL + def_bool y + depends on CPU_SUP_INTEL + menuconfig PROCESSOR_SELECT bool "Supported processor vendors" if EXPERT ---help--- diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile index a704fb9ee98e..4173b0de7a2f 100644 --- a/arch/x86/kernel/cpu/Makefile +++ b/arch/x86/kernel/cpu/Makefile @@ -32,6 +32,7 @@ obj-y += umwait.o obj-$(CONFIG_PROC_FS) += proc.o obj-$(CONFIG_X86_FEATURE_NAMES) += capflags.o powerflags.o
+obj-$(CONFIG_IA32_FEAT_CTL) += feat_ctl.o ifdef CONFIG_CPU_SUP_INTEL obj-y += intel.o intel_pconfig.o tsx.o obj-$(CONFIG_PM) += intel_epb.o diff --git a/arch/x86/kernel/cpu/cpu.h b/arch/x86/kernel/cpu/cpu.h index 38ab6e115eac..37fdefd14f28 100644 --- a/arch/x86/kernel/cpu/cpu.h +++ b/arch/x86/kernel/cpu/cpu.h @@ -80,4 +80,8 @@ extern void x86_spec_ctrl_setup_ap(void);
extern u64 x86_read_arch_cap_msr(void);
+#ifdef CONFIG_IA32_FEAT_CTL +void init_ia32_feat_ctl(struct cpuinfo_x86 *c); +#endif + #endif /* ARCH_X86_CPU_H */ diff --git a/arch/x86/kernel/cpu/feat_ctl.c b/arch/x86/kernel/cpu/feat_ctl.c new file mode 100644 index 000000000000..c4f8f767853b --- /dev/null +++ b/arch/x86/kernel/cpu/feat_ctl.c @@ -0,0 +1,37 @@ +// SPDX-License-Identifier: GPL-2.0 +#include <linux/tboot.h> + +#include <asm/cpufeature.h> +#include <asm/msr-index.h> +#include <asm/processor.h> + +void init_ia32_feat_ctl(struct cpuinfo_x86 *c) +{ + u64 msr; + + if (rdmsrl_safe(MSR_IA32_FEAT_CTL, &msr)) + return; + + if (msr & FEAT_CTL_LOCKED) + return; + + /* + * Ignore whatever value BIOS left in the MSR to avoid enabling random + * features or faulting on the WRMSR. + */ + msr = FEAT_CTL_LOCKED; + + /* + * Enable VMX if and only if the kernel may do VMXON at some point, + * i.e. KVM is enabled, to avoid unnecessarily adding an attack vector + * for the kernel, e.g. using VMX to hide malicious code. + */ + if (cpu_has(c, X86_FEATURE_VMX) && IS_ENABLED(CONFIG_KVM_INTEL)) { + msr |= FEAT_CTL_VMX_ENABLED_OUTSIDE_SMX; + + if (tboot_enabled()) + msr |= FEAT_CTL_VMX_ENABLED_INSIDE_SMX; + } + + wrmsrl(MSR_IA32_FEAT_CTL, msr); +} diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c index 4a900804a023..9129c170ea11 100644 --- a/arch/x86/kernel/cpu/intel.c +++ b/arch/x86/kernel/cpu/intel.c @@ -755,6 +755,8 @@ static void init_intel(struct cpuinfo_x86 *c) /* Work around errata */ srat_detect_node(c);
+ init_ia32_feat_ctl(c); + if (cpu_has(c, X86_FEATURE_VMX)) detect_vmx_virtcap(c);