KVM: x86: Assume a 64-bit hypercall for guests with protected state

When processing a hypercall for a guest with protected state, currently
SEV-ES guests, the guest CS segment register can't be checked to
determine if the guest is in 64-bit mode. For an SEV-ES guest, it is
expected that communication between the guest and the hypervisor is
performed to shared memory using the GHCB. In order to use the GHCB, the
guest must have been in long mode, otherwise writes by the guest to the
GHCB would be encrypted and not be able to be comprehended by the
hypervisor.

Create a new helper function, is_64_bit_hypercall(), that assumes the
guest is in 64-bit mode when the guest has protected state, and returns
true, otherwise invoking is_64_bit_mode() to determine the mode. Update
the hypercall related routines to use is_64_bit_hypercall() instead of
is_64_bit_mode().

Add a WARN_ON_ONCE() to is_64_bit_mode() to catch occurences of calls to
this helper function for a guest running with protected state.

Fixes: f1c6366e3043 ("KVM: SVM: Add required changes to support intercepts under SEV-ES")
Reported-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Message-Id: <e0b20c770c9d0d1403f23d83e785385104211f74.1621878537.git.thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 4a555f32885a8c489c7f70750956d08fa545d0f4..5e19e6e4c2ce0b5d357ce04eccb5a7cecf9c478b 100644 (file)
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -2022,7 +2022,7 @@ static void kvm_hv_hypercall_set_result(struct kvm_vcpu *vcpu, u64 result)
 {
        bool longmode;
 
-       longmode = is_64_bit_mode(vcpu);
+       longmode = is_64_bit_hypercall(vcpu);
        if (longmode)
                kvm_rax_write(vcpu, result);
        else {
@@ -2171,7 +2171,7 @@ int kvm_hv_hypercall(struct kvm_vcpu *vcpu)
        }
 
 #ifdef CONFIG_X86_64
-       if (is_64_bit_mode(vcpu)) {
+       if (is_64_bit_hypercall(vcpu)) {
                hc.param = kvm_rcx_read(vcpu);
                hc.ingpa = kvm_rdx_read(vcpu);
                hc.outgpa = kvm_r8_read(vcpu);

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c85d70107057a41bbef4da893e545fc93c6a2562..ecd2041570d14ad81dc4359768f5eb3dd5ba1a15 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -8848,7 +8848,7 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu)
 
        trace_kvm_hypercall(nr, a0, a1, a2, a3);
 
-       op_64_bit = is_64_bit_mode(vcpu);
+       op_64_bit = is_64_bit_hypercall(vcpu);
        if (!op_64_bit) {
                nr &= 0xFFFFFFFF;
                a0 &= 0xFFFFFFFF;

diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index ea264c4502e413f699e836065e868bcc20865289..997669ae9caa21749d2339a48e761132b04201fd 100644 (file)
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -153,12 +153,24 @@ static inline bool is_64_bit_mode(struct kvm_vcpu *vcpu)
 {
        int cs_db, cs_l;
 
+       WARN_ON_ONCE(vcpu->arch.guest_state_protected);
+
        if (!is_long_mode(vcpu))
                return false;
        static_call(kvm_x86_get_cs_db_l_bits)(vcpu, &cs_db, &cs_l);
        return cs_l;
 }
 
+static inline bool is_64_bit_hypercall(struct kvm_vcpu *vcpu)
+{
+       /*
+        * If running with protected guest state, the CS register is not
+        * accessible. The hypercall register values will have had to been
+        * provided in 64-bit mode, so assume the guest is in 64-bit.
+        */
+       return vcpu->arch.guest_state_protected || is_64_bit_mode(vcpu);
+}
+
 static inline bool x86_exception_has_error_code(unsigned int vector)
 {
        static u32 exception_has_error_code = BIT(DF_VECTOR) | BIT(TS_VECTOR) |

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 565da9c3853bf4807afaa0dc3a34504b33758287..dff2bdf9507a8cf679f449b277666df1ccf34773 100644 (file)
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -698,7 +698,7 @@ int kvm_xen_hypercall(struct kvm_vcpu *vcpu)
            kvm_hv_hypercall_enabled(vcpu))
                return kvm_hv_hypercall(vcpu);
 
-       longmode = is_64_bit_mode(vcpu);
+       longmode = is_64_bit_hypercall(vcpu);
        if (!longmode) {
                params[0] = (u32)kvm_rbx_read(vcpu);
                params[1] = (u32)kvm_rcx_read(vcpu);