arm64: KVM: Survive unknown traps from guests

Currently we BUG() if we see an ESR_EL2.EC value we don't recognise. As
configurable disables/enables are added to the architecture (controlled
by RES1/RES0 bits respectively), with associated synchronous exceptions,
it may be possible for a guest to trigger exceptions with classes that
we don't recognise.

While we can't service these exceptions in a manner useful to the guest,
we can avoid bringing down the host. Per ARM DDI 0487A.k_iss10775, page
D7-1937, EC values within the range 0x00 - 0x2c are reserved for future
use with synchronous exceptions, and EC values within the range 0x2d -
0x3f may be used for either synchronous or asynchronous exceptions.

The patch makes KVM handle any unknown EC by injecting an UNDEFINED
exception into the guest, with a corresponding (ratelimited) warning in
the host dmesg. We could later improve on this with with a new (opt-in)
exit to the host userspace.

Cc: Dave Martin <dave.martin@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c
index 1bfe30dfbfe77ffa2395528e008c058bd93b648d..fa1b18e364fc9d73cec1c0fdb6626285c1d7adc2 100644 (file)
--- a/arch/arm64/kvm/handle_exit.c
+++ b/arch/arm64/kvm/handle_exit.c
@@ -135,7 +135,19 @@ static int kvm_handle_guest_debug(struct kvm_vcpu *vcpu, struct kvm_run *run)
        return ret;
 }
 
+static int kvm_handle_unknown_ec(struct kvm_vcpu *vcpu, struct kvm_run *run)
+{
+       u32 hsr = kvm_vcpu_get_hsr(vcpu);
+
+       kvm_pr_unimpl("Unknown exception class: hsr: %#08x -- %s\n",
+                     hsr, esr_get_class_string(hsr));
+
+       kvm_inject_undefined(vcpu);
+       return 1;
+}
+
 static exit_handle_fn arm_exit_handlers[] = {
+       [0 ... ESR_ELx_EC_MAX]  = kvm_handle_unknown_ec,
        [ESR_ELx_EC_WFx]        = kvm_handle_wfx,
        [ESR_ELx_EC_CP15_32]    = kvm_handle_cp15_32,
        [ESR_ELx_EC_CP15_64]    = kvm_handle_cp15_64,
@@ -162,13 +174,6 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
        u32 hsr = kvm_vcpu_get_hsr(vcpu);
        u8 hsr_ec = ESR_ELx_EC(hsr);
 
-       if (hsr_ec >= ARRAY_SIZE(arm_exit_handlers) ||
-           !arm_exit_handlers[hsr_ec]) {
-               kvm_err("Unknown exception class: hsr: %#08x -- %s\n",
-                       hsr, esr_get_class_string(hsr));
-               BUG();
-       }
-
        return arm_exit_handlers[hsr_ec];
 }