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KVM: SEV: remove ghcb variable declarations

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To avoid possible time-of-check/time-of-use issues, the GHCB should
almost never be accessed outside dump_ghcb, sev_es_sync_to_ghcb
and sev_es_sync_from_ghcb.  The only legitimate uses are to set the
exitinfo fields and to find the address of the scratch area embedded
in the ghcb.  Accessing ghcb_usage also goes through svm->sev_es.ghcb
in sev_es_validate_vmgexit(), but that is because anyway the value is
not used.

Removing a shortcut variable that contains the value of svm->sev_es.ghcb
makes these cases a bit more verbose, but it limits the chance of someone
reading the ghcb by mistake.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2023-08-04 13:01:43 -04:00
parent 7588dbcebc
commit 63dbc67cf4
1 changed files with 12 additions and 18 deletions
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30
arch/x86/kvm/svm/sev.c
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@ -2454,12 +2454,9 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
{
struct vmcb_control_area *control = &svm->vmcb->control;
struct kvm_vcpu *vcpu = &svm->vcpu;
struct ghcb *ghcb;
u64 exit_code;
u64 reason;
ghcb = svm->sev_es.ghcb;
/*
* Retrieve the exit code now even though it may not be marked valid
* as it could help with debugging.
@ -2467,7 +2464,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
exit_code = kvm_ghcb_get_sw_exit_code(control);
/* Only GHCB Usage code 0 is supported */
if (ghcb->ghcb_usage) {
if (svm->sev_es.ghcb->ghcb_usage) {
reason = GHCB_ERR_INVALID_USAGE;
goto vmgexit_err;
}
@ -2561,7 +2558,7 @@ static int sev_es_validate_vmgexit(struct vcpu_svm *svm)
vmgexit_err:
if (reason == GHCB_ERR_INVALID_USAGE) {
vcpu_unimpl(vcpu, "vmgexit: ghcb usage %#x is not valid\n",
ghcb->ghcb_usage);
svm->sev_es.ghcb->ghcb_usage);
} else if (reason == GHCB_ERR_INVALID_EVENT) {
vcpu_unimpl(vcpu, "vmgexit: exit code %#llx is not valid\n",
exit_code);
@ -2571,8 +2568,8 @@ vmgexit_err:
dump_ghcb(svm);
}
ghcb_set_sw_exit_info_1(ghcb, 2);
ghcb_set_sw_exit_info_2(ghcb, reason);
ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, reason);
/* Resume the guest to "return" the error code. */
return 1;
@ -2637,7 +2634,6 @@ void pre_sev_run(struct vcpu_svm *svm, int cpu)
static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
{
struct vmcb_control_area *control = &svm->vmcb->control;
struct ghcb *ghcb = svm->sev_es.ghcb;
u64 ghcb_scratch_beg, ghcb_scratch_end;
u64 scratch_gpa_beg, scratch_gpa_end;
void *scratch_va;
@ -2713,8 +2709,8 @@ static int setup_vmgexit_scratch(struct vcpu_svm *svm, bool sync, u64 len)
return 0;
e_scratch:
ghcb_set_sw_exit_info_1(ghcb, 2);
ghcb_set_sw_exit_info_2(ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_SCRATCH_AREA);
return 1;
}
@ -2827,7 +2823,6 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
struct vcpu_svm *svm = to_svm(vcpu);
struct vmcb_control_area *control = &svm->vmcb->control;
u64 ghcb_gpa, exit_code;
struct ghcb *ghcb;
int ret;
/* Validate the GHCB */
@ -2852,17 +2847,16 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
}
svm->sev_es.ghcb = svm->sev_es.ghcb_map.hva;
ghcb = svm->sev_es.ghcb_map.hva;
trace_kvm_vmgexit_enter(vcpu->vcpu_id, ghcb);
trace_kvm_vmgexit_enter(vcpu->vcpu_id, svm->sev_es.ghcb);
sev_es_sync_from_ghcb(svm);
ret = sev_es_validate_vmgexit(svm);
if (ret)
return ret;
ghcb_set_sw_exit_info_1(ghcb, 0);
ghcb_set_sw_exit_info_2(ghcb, 0);
ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 0);
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, 0);
exit_code = kvm_ghcb_get_sw_exit_code(control);
switch (exit_code) {
@ -2902,13 +2896,13 @@ int sev_handle_vmgexit(struct kvm_vcpu *vcpu)
break;
case 1:
/* Get AP jump table address */
ghcb_set_sw_exit_info_2(ghcb, sev->ap_jump_table);
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, sev->ap_jump_table);
break;
default:
pr_err("svm: vmgexit: unsupported AP jump table request - exit_info_1=%#llx\n",
control->exit_info_1);
ghcb_set_sw_exit_info_1(ghcb, 2);
ghcb_set_sw_exit_info_2(ghcb, GHCB_ERR_INVALID_INPUT);
ghcb_set_sw_exit_info_1(svm->sev_es.ghcb, 2);
ghcb_set_sw_exit_info_2(svm->sev_es.ghcb, GHCB_ERR_INVALID_INPUT);
}
ret = 1;