[PATCH kvmtool v3 7/9] arm64: Make ptrauth enable/disable diagnostics more user-friendly

Dave Martin
2019-05-30T15:14:23Z

To help the user understand what is going on, amend ptrauth
configuration diagnostic messages to refer to command line options
by the exact name used on the command line.

Also, provide a clean diagnostic when ptrauth is requested, but not
availble. The generic "Unable to initialise vcpu" message is
rather cryptic for this case.

Since we now don't attempt to enable ptrauth at all unless KVM
reports the relevant capabilities, remove the error message for
that case too: in any case, we can't diagnose precisely why
KVM_ARM_VCPU_INIT failed, so the message may be misleading.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>
---
arm/aarch64/include/kvm/kvm-config-arch.h | 4 ++--
arm/aarch64/kvm-cpu.c | 15 +++++++++++----
arm/kvm-cpu.c | 8 ++------
3 files changed, 15 insertions(+), 12 deletions(-)

diff --git a/arm/aarch64/include/kvm/kvm-config-arch.h b/arm/aarch64/include/kvm/kvm-config-arch.h
index 0279b13..fe1699d 100644
--- a/arm/aarch64/include/kvm/kvm-config-arch.h
+++ b/arm/aarch64/include/kvm/kvm-config-arch.h
@@ -10,9 +10,9 @@
"Specify random seed for Kernel Address Space " \
"Layout Randomization (KASLR)"), \
OPT_BOOLEAN('\0', "enable-ptrauth", &(cfg)->enable_ptrauth, \
- "Enables pointer authentication"), \
+ "Enable pointer authentication for the guest"), \
OPT_BOOLEAN('\0', "disable-ptrauth", &(cfg)->disable_ptrauth, \
- "Disables pointer authentication"),
+ "Disable pointer authentication for the guest"),

#include "arm-common/kvm-config-arch.h"

diff --git a/arm/aarch64/kvm-cpu.c b/arm/aarch64/kvm-cpu.c
index d3c32e0..08e4fd5 100644
--- a/arm/aarch64/kvm-cpu.c
+++ b/arm/aarch64/kvm-cpu.c
@@ -130,16 +130,23 @@ static void reset_vcpu_aarch64(struct kvm_cpu *vcpu)

static void select_ptrauth_feature(struct kvm *kvm, struct kvm_vcpu_init *init)
{
+ bool supported;
+
/* Check Pointer Authentication command line arguments. */
if (kvm->cfg.arch.enable_ptrauth && kvm->cfg.arch.disable_ptrauth)
- die("Both enable-ptrauth and disable-ptrauth option cannot be present");
+ die("--enable-ptrauth conflicts with --disable-ptrauth");
+
+ supported = kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
+ kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC);
+
+ if (kvm->cfg.arch.enable_ptrauth && !supported)
+ die("--enable-ptrauth not supported on this host");
+
/*
* Always enable Pointer Authentication if system supports
* this extension unless disable-ptrauth option is present.
*/
- if (kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_ADDRESS) &&
- kvm__supports_extension(kvm, KVM_CAP_ARM_PTRAUTH_GENERIC) &&
- !kvm->cfg.arch.disable_ptrauth) {
+ if (supported && !kvm->cfg.arch.disable_ptrauth) {
init->features[0] |= 1UL << KVM_ARM_VCPU_PTRAUTH_ADDRESS;
init->features[0] |= 1UL << KVM_ARM_VCPU_PTRAUTH_GENERIC;
}
diff --git a/arm/kvm-cpu.c b/arm/kvm-cpu.c
index 764fb05..1652f6f 100644
--- a/arm/kvm-cpu.c
+++ b/arm/kvm-cpu.c
@@ -108,12 +108,8 @@ struct kvm_cpu *kvm_cpu__arch_init(struct kvm *kvm, unsigned long cpu_id)
die("Unable to find matching target");
}

- if (err || target->init(vcpu)) {
- if (kvm->cfg.arch.enable_ptrauth)
- die("Unable to initialise vcpu with pointer authentication feature");
- else
- die("Unable to initialise vcpu");
- }
+ if (err || target->init(vcpu))
+ die("Unable to initialise vcpu");

coalesced_offset = ioctl(kvm->sys_fd, KVM_CHECK_EXTENSION,
KVM_CAP_COALESCED_MMIO);
--
2.1.4