hw/arm/virt: KVM: Enable PAuth when supported by the host

Add basic support for Pointer Authentication when running a KVM
guest and that the host supports it, loosely based on the SVE
support.

Although the feature is enabled by default when the host advertises
it, it is possible to disable it by setting the 'pauth=off' CPU
property. The 'pauth' comment is removed from cpu-features.rst,
as it is now common to both TCG and KVM.

Tested on an Apple M1 running 5.16-rc6.

Cc: Eric Auger <eric.auger@redhat.com>
Cc: Richard Henderson <richard.henderson@linaro.org>
Cc: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20220107150154.2490308-1-maz@kernel.org
[PMM: fixed indentation]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

1 files changed, 27 insertions, 4 deletions

diff --git a/target/arm/cpu64.c b/target/arm/cpu64.c
index 15245a60a8..8786be7783 100644
--- a/target/arm/cpu64.c
+++ b/target/arm/cpu64.c
@@ -630,6 +630,15 @@ void arm_cpu_pauth_finalize(ARMCPU *cpu, Error **errp)
     int arch_val = 0, impdef_val = 0;
     uint64_t t;
 
+    /* Exit early if PAuth is enabled, and fall through to disable it */
+    if (kvm_enabled() && cpu->prop_pauth) {
+        if (!cpu_isar_feature(aa64_pauth, cpu)) {
+            error_setg(errp, "'pauth' feature not supported by KVM on this host");
+        }
+
+        return;
+    }
+
     /* TODO: Handle HaveEnhancedPAC, HaveEnhancedPAC2, HaveFPAC. */
     if (cpu->prop_pauth) {
         if (cpu->prop_pauth_impdef) {
@@ -655,6 +664,23 @@ static Property arm_cpu_pauth_property =
 static Property arm_cpu_pauth_impdef_property =
     DEFINE_PROP_BOOL("pauth-impdef", ARMCPU, prop_pauth_impdef, false);
 
+void aarch64_add_pauth_properties(Object *obj)
+{
+    ARMCPU *cpu = ARM_CPU(obj);
+
+    /* Default to PAUTH on, with the architected algorithm on TCG. */
+    qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_property);
+    if (kvm_enabled()) {
+        /*
+         * Mirror PAuth support from the probed sysregs back into the
+         * property for KVM. Is it just a bit backward? Yes it is!
+         */
+        cpu->prop_pauth = cpu_isar_feature(aa64_pauth, cpu);
+    } else {
+        qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_impdef_property);
+    }
+}
+
 /* -cpu max: if KVM is enabled, like -cpu host (best possible with this host);
  * otherwise, a CPU with as many features enabled as our emulation supports.
  * The version of '-cpu max' for qemu-system-arm is defined in cpu.c;
@@ -829,13 +855,10 @@ static void aarch64_max_initfn(Object *obj)
         cpu->dcz_blocksize = 7; /*  512 bytes */
 #endif
 
-        /* Default to PAUTH on, with the architected algorithm. */
-        qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_property);
-        qdev_property_add_static(DEVICE(obj), &arm_cpu_pauth_impdef_property);
-
         bitmap_fill(cpu->sve_vq_supported, ARM_MAX_VQ);
     }
 
+    aarch64_add_pauth_properties(obj);
     aarch64_add_sve_properties(obj);
     object_property_add(obj, "sve-max-vq", "uint32", cpu_max_get_sve_max_vq,
                         cpu_max_set_sve_max_vq, NULL, NULL);