From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
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@xxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kvm/svm/sev.c | 69 ++++++++++++++++++++++++-------------------------
arch/x86/kvm/svm/svm.h | 26 ++++++++++++++++++
2 files changed, 61 insertions(+), 34 deletions(-)
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -2414,15 +2414,18 @@ static void sev_es_sync_from_ghcb(struct
*/
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);
}
@@ -2433,6 +2436,7 @@ static void sev_es_sync_from_ghcb(struct
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));
@@ -2461,56 +2465,56 @@ static int sev_es_validate_vmgexit(struc
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:
@@ -2518,19 +2522,19 @@ static int sev_es_validate_vmgexit(struc
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:
@@ -2560,9 +2564,6 @@ 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);
@@ -2583,7 +2584,7 @@ void sev_es_unmap_ghcb(struct vcpu_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;
@@ -2634,7 +2635,7 @@ static int setup_vmgexit_scratch(struct
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;
@@ -2850,11 +2851,11 @@ int sev_handle_vmgexit(struct kvm_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);
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -190,10 +190,12 @@ 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;
@@ -745,4 +747,28 @@ void sev_es_unmap_ghcb(struct vcpu_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
