From: Sean Christopherson Date: Fri, 19 Sep 2025 22:32:09 +0000 (-0700) Subject: KVM: SEV: Read save fields from GHCB exactly once X-Git-Tag: v6.18-rc1~55^2~8^2~11 X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=bd5f500d23170e5bde59ce97da523048b66a8183;p=thirdparty%2Fkernel%2Flinux.git KVM: SEV: Read save fields from GHCB exactly once Wrap all reads of GHCB save fields with READ_ONCE() via a KVM-specific GHCB get() utility to help guard against TOCTOU bugs. Using READ_ONCE() doesn't completely prevent such bugs, e.g. doesn't prevent KVM from redoing get() after checking the initial value, but at least addresses all potential TOCTOU issues in the current KVM code base. To prevent unintentional use of the generic helpers, take only @svm for the kvm_ghcb_get_xxx() helpers and retrieve the ghcb instead of explicitly passing it in. Opportunistically reduce the indentation of the macro-defined helpers and clean up the alignment. Fixes: 4e15a0ddc3ff ("KVM: SEV: snapshot the GHCB before accessing it") Reviewed-by: Tom Lendacky Link: https://lore.kernel.org/r/20250919223258.1604852-3-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c index 5456a71f95040..a2076ab3fe71c 100644 --- a/arch/x86/kvm/svm/sev.c +++ b/arch/x86/kvm/svm/sev.c @@ -3299,26 +3299,26 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm) BUILD_BUG_ON(sizeof(svm->sev_es.valid_bitmap) != sizeof(ghcb->save.valid_bitmap)); memcpy(&svm->sev_es.valid_bitmap, &ghcb->save.valid_bitmap, sizeof(ghcb->save.valid_bitmap)); - vcpu->arch.regs[VCPU_REGS_RAX] = kvm_ghcb_get_rax_if_valid(svm, ghcb); - vcpu->arch.regs[VCPU_REGS_RBX] = kvm_ghcb_get_rbx_if_valid(svm, ghcb); - vcpu->arch.regs[VCPU_REGS_RCX] = kvm_ghcb_get_rcx_if_valid(svm, ghcb); - vcpu->arch.regs[VCPU_REGS_RDX] = kvm_ghcb_get_rdx_if_valid(svm, ghcb); - vcpu->arch.regs[VCPU_REGS_RSI] = kvm_ghcb_get_rsi_if_valid(svm, ghcb); + vcpu->arch.regs[VCPU_REGS_RAX] = kvm_ghcb_get_rax_if_valid(svm); + vcpu->arch.regs[VCPU_REGS_RBX] = kvm_ghcb_get_rbx_if_valid(svm); + vcpu->arch.regs[VCPU_REGS_RCX] = kvm_ghcb_get_rcx_if_valid(svm); + vcpu->arch.regs[VCPU_REGS_RDX] = kvm_ghcb_get_rdx_if_valid(svm); + vcpu->arch.regs[VCPU_REGS_RSI] = kvm_ghcb_get_rsi_if_valid(svm); - svm->vmcb->save.cpl = kvm_ghcb_get_cpl_if_valid(svm, ghcb); + svm->vmcb->save.cpl = kvm_ghcb_get_cpl_if_valid(svm); if (kvm_ghcb_xcr0_is_valid(svm)) { - vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb); + vcpu->arch.xcr0 = kvm_ghcb_get_xcr0(svm); vcpu->arch.cpuid_dynamic_bits_dirty = true; } /* Copy the GHCB exit information into the VMCB fields */ - exit_code = ghcb_get_sw_exit_code(ghcb); + exit_code = kvm_ghcb_get_sw_exit_code(svm); control->exit_code = lower_32_bits(exit_code); control->exit_code_hi = upper_32_bits(exit_code); - control->exit_info_1 = ghcb_get_sw_exit_info_1(ghcb); - control->exit_info_2 = ghcb_get_sw_exit_info_2(ghcb); - svm->sev_es.sw_scratch = kvm_ghcb_get_sw_scratch_if_valid(svm, ghcb); + control->exit_info_1 = kvm_ghcb_get_sw_exit_info_1(svm); + control->exit_info_2 = kvm_ghcb_get_sw_exit_info_2(svm); + svm->sev_es.sw_scratch = kvm_ghcb_get_sw_scratch_if_valid(svm); /* Clear the valid entries fields */ memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap)); diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h index 3c7f208b79352..10d5cbc259e1c 100644 --- a/arch/x86/kvm/svm/svm.h +++ b/arch/x86/kvm/svm/svm.h @@ -913,16 +913,21 @@ void __svm_sev_es_vcpu_run(struct vcpu_svm *svm, bool spec_ctrl_intercepted, void __svm_vcpu_run(struct vcpu_svm *svm, bool spec_ctrl_intercepted); #define DEFINE_KVM_GHCB_ACCESSORS(field) \ - static __always_inline bool kvm_ghcb_##field##_is_valid(const struct vcpu_svm *svm) \ - { \ - return test_bit(GHCB_BITMAP_IDX(field), \ - (unsigned long *)&svm->sev_es.valid_bitmap); \ - } \ - \ - static __always_inline u64 kvm_ghcb_get_##field##_if_valid(struct vcpu_svm *svm, struct ghcb *ghcb) \ - { \ - return kvm_ghcb_##field##_is_valid(svm) ? ghcb->save.field : 0; \ - } \ +static __always_inline u64 kvm_ghcb_get_##field(struct vcpu_svm *svm) \ +{ \ + return READ_ONCE(svm->sev_es.ghcb->save.field); \ +} \ + \ +static __always_inline bool kvm_ghcb_##field##_is_valid(const struct vcpu_svm *svm) \ +{ \ + return test_bit(GHCB_BITMAP_IDX(field), \ + (unsigned long *)&svm->sev_es.valid_bitmap); \ +} \ + \ +static __always_inline u64 kvm_ghcb_get_##field##_if_valid(struct vcpu_svm *svm) \ +{ \ + return kvm_ghcb_##field##_is_valid(svm) ? kvm_ghcb_get_##field(svm) : 0; \ +} DEFINE_KVM_GHCB_ACCESSORS(cpl) DEFINE_KVM_GHCB_ACCESSORS(rax)