diff options
| author | Yang Weijiang <weijiang.yang@intel.com> | 2025-09-19 15:32:24 -0700 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2025-09-23 09:11:49 -0700 |
| commit | 584ba3ffb9843fd12d3b4a33cfe056e2264392a0 (patch) | |
| tree | 7ac2556303a9a1e65a7e01457b34064593296592 /arch/x86/kvm/x86.c | |
| parent | KVM: VMX: Set up interception for CET MSRs (diff) | |
| download | linux-584ba3ffb9843fd12d3b4a33cfe056e2264392a0.tar.gz linux-584ba3ffb9843fd12d3b4a33cfe056e2264392a0.zip | |
KVM: VMX: Set host constant supervisor states to VMCS fields
Save constant values to HOST_{S_CET,SSP,INTR_SSP_TABLE} field explicitly.
Kernel IBT is supported and the setting in MSR_IA32_S_CET is static after
post-boot(The exception is BIOS call case but vCPU thread never across it)
and KVM doesn't need to refresh HOST_S_CET field before every VM-Enter/
VM-Exit sequence.
Host supervisor shadow stack is not enabled now and SSP is not accessible
to kernel mode, thus it's safe to set host IA32_INT_SSP_TAB/SSP VMCS field
to 0s. When shadow stack is enabled for CPL3, SSP is reloaded from PL3_SSP
before it exits to userspace. Check SDM Vol 2A/B Chapter 3/4 for SYSCALL/
SYSRET/SYSENTER SYSEXIT/RDSSP/CALL etc.
Prevent KVM module loading if host supervisor shadow stack SHSTK_EN is set
in MSR_IA32_S_CET as KVM cannot co-exit with it correctly.
Suggested-by: Sean Christopherson <seanjc@google.com>
Suggested-by: Chao Gao <chao.gao@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
[sean: snapshot host S_CET if SHSTK *or* IBT is supported]
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-18-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 54d280fe9a4b..0050509a7de2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -9997,6 +9997,18 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops) return -EIO; } + if (boot_cpu_has(X86_FEATURE_SHSTK) || boot_cpu_has(X86_FEATURE_IBT)) { + rdmsrq(MSR_IA32_S_CET, kvm_host.s_cet); + /* + * Linux doesn't yet support supervisor shadow stacks (SSS), so + * KVM doesn't save/restore the associated MSRs, i.e. KVM may + * clobber the host values. Yell and refuse to load if SSS is + * unexpectedly enabled, e.g. to avoid crashing the host. + */ + if (WARN_ON_ONCE(kvm_host.s_cet & CET_SHSTK_EN)) + return -EIO; + } + memset(&kvm_caps, 0, sizeof(kvm_caps)); x86_emulator_cache = kvm_alloc_emulator_cache(); |