KVM: SEV: snapshot the GHCB before accessing it

commit 4e15a0ddc3ff40e8ea84032213976ecf774d7f77 upstream.

Validation of the GHCB is susceptible to time-of-check/time-of-use vulnerabilities.
To avoid them, we would like to always snapshot the fields that are read in
sev_es_validate_vmgexit(), and not use the GHCB anymore after it returns.

This means:

- invoking sev_es_sync_from_ghcb() before any GHCB access, including before
  sev_es_validate_vmgexit()

- snapshotting all fields including the valid bitmap and the sw_scratch field,
  which are currently not caching anywhere.

The valid bitmap is the first thing to be copied out of the GHCB; then,
further accesses will use the copy in svm->sev_es.

Fixes: 291bd20d5d88 ("KVM: SVM: Add initial support for a VMGEXIT VMEXIT")
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 4cb2e48..38fbe9d 100644 (file)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2410,15 +2410,18 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm)
         */
        memset(vcpu->arch.regs, 0, sizeof(vcpu->arch.regs));
 
-       vcpu->arch.regs[VCPU_REGS_RAX] = ghcb_get_rax_if_valid(ghcb);
-       vcpu->arch.regs[VCPU_REGS_RBX] = ghcb_get_rbx_if_valid(ghcb);
-       vcpu->arch.regs[VCPU_REGS_RCX] = ghcb_get_rcx_if_valid(ghcb);
-       vcpu->arch.regs[VCPU_REGS_RDX] = ghcb_get_rdx_if_valid(ghcb);
-       vcpu->arch.regs[VCPU_REGS_RSI] = ghcb_get_rsi_if_valid(ghcb);
+       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));
 
-       svm->vmcb->save.cpl = ghcb_get_cpl_if_valid(ghcb);
+       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);
 
-       if (ghcb_xcr0_is_valid(ghcb)) {
+       svm->vmcb->save.cpl = kvm_ghcb_get_cpl_if_valid(svm, ghcb);
+
+       if (kvm_ghcb_xcr0_is_valid(svm)) {
                vcpu->arch.xcr0 = ghcb_get_xcr0(ghcb);
                kvm_update_cpuid_runtime(vcpu);
        }
@@ -2429,6 +2432,7 @@ static void sev_es_sync_from_ghcb(struct vcpu_svm *svm)
        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);
 
        /* Clear the valid entries fields */
        memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
@@ -2457,56 +2461,56 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
 
        reason = GHCB_ERR_MISSING_INPUT;
 
-       if (!ghcb_sw_exit_code_is_valid(ghcb) ||
-           !ghcb_sw_exit_info_1_is_valid(ghcb) ||
-           !ghcb_sw_exit_info_2_is_valid(ghcb))
+       if (!kvm_ghcb_sw_exit_code_is_valid(svm) ||
+           !kvm_ghcb_sw_exit_info_1_is_valid(svm) ||
+           !kvm_ghcb_sw_exit_info_2_is_valid(svm))
                goto vmgexit_err;
 
        switch (ghcb_get_sw_exit_code(ghcb)) {
        case SVM_EXIT_READ_DR7:
                break;
        case SVM_EXIT_WRITE_DR7:
-               if (!ghcb_rax_is_valid(ghcb))
+               if (!kvm_ghcb_rax_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_EXIT_RDTSC:
                break;
        case SVM_EXIT_RDPMC:
-               if (!ghcb_rcx_is_valid(ghcb))
+               if (!kvm_ghcb_rcx_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_EXIT_CPUID:
-               if (!ghcb_rax_is_valid(ghcb) ||
-                   !ghcb_rcx_is_valid(ghcb))
+               if (!kvm_ghcb_rax_is_valid(svm) ||
+                   !kvm_ghcb_rcx_is_valid(svm))
                        goto vmgexit_err;
                if (ghcb_get_rax(ghcb) == 0xd)
-                       if (!ghcb_xcr0_is_valid(ghcb))
+                       if (!kvm_ghcb_xcr0_is_valid(svm))
                                goto vmgexit_err;
                break;
        case SVM_EXIT_INVD:
                break;
        case SVM_EXIT_IOIO:
                if (ghcb_get_sw_exit_info_1(ghcb) & SVM_IOIO_STR_MASK) {
-                       if (!ghcb_sw_scratch_is_valid(ghcb))
+                       if (!kvm_ghcb_sw_scratch_is_valid(svm))
                                goto vmgexit_err;
                } else {
                        if (!(ghcb_get_sw_exit_info_1(ghcb) & SVM_IOIO_TYPE_MASK))
-                               if (!ghcb_rax_is_valid(ghcb))
+                               if (!kvm_ghcb_rax_is_valid(svm))
                                        goto vmgexit_err;
                }
                break;
        case SVM_EXIT_MSR:
-               if (!ghcb_rcx_is_valid(ghcb))
+               if (!kvm_ghcb_rcx_is_valid(svm))
                        goto vmgexit_err;
                if (ghcb_get_sw_exit_info_1(ghcb)) {
-                       if (!ghcb_rax_is_valid(ghcb) ||
-                           !ghcb_rdx_is_valid(ghcb))
+                       if (!kvm_ghcb_rax_is_valid(svm) ||
+                           !kvm_ghcb_rdx_is_valid(svm))
                                goto vmgexit_err;
                }
                break;
        case SVM_EXIT_VMMCALL:
-               if (!ghcb_rax_is_valid(ghcb) ||
-                   !ghcb_cpl_is_valid(ghcb))
+               if (!kvm_ghcb_rax_is_valid(svm) ||
+                   !kvm_ghcb_cpl_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_EXIT_RDTSCP:
@@ -2514,19 +2518,19 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
        case SVM_EXIT_WBINVD:
                break;
        case SVM_EXIT_MONITOR:
-               if (!ghcb_rax_is_valid(ghcb) ||
-                   !ghcb_rcx_is_valid(ghcb) ||
-                   !ghcb_rdx_is_valid(ghcb))
+               if (!kvm_ghcb_rax_is_valid(svm) ||
+                   !kvm_ghcb_rcx_is_valid(svm) ||
+                   !kvm_ghcb_rdx_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_EXIT_MWAIT:
-               if (!ghcb_rax_is_valid(ghcb) ||
-                   !ghcb_rcx_is_valid(ghcb))
+               if (!kvm_ghcb_rax_is_valid(svm) ||
+                   !kvm_ghcb_rcx_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_VMGEXIT_MMIO_READ:
        case SVM_VMGEXIT_MMIO_WRITE:
-               if (!ghcb_sw_scratch_is_valid(ghcb))
+               if (!kvm_ghcb_sw_scratch_is_valid(svm))
                        goto vmgexit_err;
                break;
        case SVM_VMGEXIT_NMI_COMPLETE:
@@ -2556,9 +2560,6 @@ vmgexit_err:
                dump_ghcb(svm);
        }
 
-       /* Clear the valid entries fields */
-       memset(ghcb->save.valid_bitmap, 0, sizeof(ghcb->save.valid_bitmap));
-
        ghcb_set_sw_exit_info_1(ghcb, 2);
        ghcb_set_sw_exit_info_2(ghcb, reason);
 
@@ -2579,7 +2580,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm)
                 */
                if (svm->sev_es.ghcb_sa_sync) {
                        kvm_write_guest(svm->vcpu.kvm,
-                                       ghcb_get_sw_scratch(svm->sev_es.ghcb),
+                                       svm->sev_es.sw_scratch,
                                        svm->sev_es.ghcb_sa,
                                        svm->sev_es.ghcb_sa_len);
                        svm->sev_es.ghcb_sa_sync = false;
@@ -2630,7 +2631,7 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
        u64 scratch_gpa_beg, scratch_gpa_end;
        void *scratch_va;
 
-       scratch_gpa_beg = ghcb_get_sw_scratch(ghcb);
+       scratch_gpa_beg = svm->sev_es.sw_scratch;
        if (!scratch_gpa_beg) {
                pr_err("vmgexit: scratch gpa not provided\n");
                goto e_scratch;
@@ -2846,11 +2847,11 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
 
        exit_code = ghcb_get_sw_exit_code(ghcb);
 
+       sev_es_sync_from_ghcb(svm);
        ret = sev_es_validate_vmgexit(svm);
        if (ret)
                return ret;
 
-       sev_es_sync_from_ghcb(svm);
        ghcb_set_sw_exit_info_1(ghcb, 0);
        ghcb_set_sw_exit_info_2(ghcb, 0);
 

diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index d0ed3f5..62f8749 100644 (file)
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -196,10 +196,12 @@ struct vcpu_sev_es_state {
        /* SEV-ES support */
        struct sev_es_save_area *vmsa;
        struct ghcb *ghcb;
+       u8 valid_bitmap[16];
        struct kvm_host_map ghcb_map;
        bool received_first_sipi;
 
        /* SEV-ES scratch area support */
+       u64 sw_scratch;
        void *ghcb_sa;
        u32 ghcb_sa_len;
        bool ghcb_sa_sync;
@@ -688,4 +690,28 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
 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; \
+       }                                                                       \
+
+DEFINE_KVM_GHCB_ACCESSORS(cpl)
+DEFINE_KVM_GHCB_ACCESSORS(rax)
+DEFINE_KVM_GHCB_ACCESSORS(rcx)
+DEFINE_KVM_GHCB_ACCESSORS(rdx)
+DEFINE_KVM_GHCB_ACCESSORS(rbx)
+DEFINE_KVM_GHCB_ACCESSORS(rsi)
+DEFINE_KVM_GHCB_ACCESSORS(sw_exit_code)
+DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_1)
+DEFINE_KVM_GHCB_ACCESSORS(sw_exit_info_2)
+DEFINE_KVM_GHCB_ACCESSORS(sw_scratch)
+DEFINE_KVM_GHCB_ACCESSORS(xcr0)
+
 #endif