arm: KVM: Survive unknown traps from guests

Currently we BUG() if we see a HSR.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 0406C.c, all currently
unallocated HSR EC encodings are reserved, and per ARM DDI
0487A.k_iss10775, page G6-4395, 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/arm/include/asm/kvm_arm.h b/arch/arm/include/asm/kvm_arm.h
index e22089fb44dc86b7ed2fdb175bc6ec7b47ee4001..a3f0b3d500895b349004921b5f1b9435a45a0f5b 100644 (file)
--- a/arch/arm/include/asm/kvm_arm.h
+++ b/arch/arm/include/asm/kvm_arm.h
@@ -209,6 +209,7 @@
 #define HSR_EC_IABT_HYP        (0x21)
 #define HSR_EC_DABT    (0x24)
 #define HSR_EC_DABT_HYP        (0x25)
+#define HSR_EC_MAX     (0x3f)
 
 #define HSR_WFI_IS_WFE         (_AC(1, UL) << 0)
 

diff --git a/arch/arm/kvm/handle_exit.c b/arch/arm/kvm/handle_exit.c
index 4e40d1955e35341b7756efe72f2da6bf2360b224..96af65a30d78b1e09182d8e41f8b8e3ff4aae81e 100644 (file)
--- a/arch/arm/kvm/handle_exit.c
+++ b/arch/arm/kvm/handle_exit.c
@@ -79,7 +79,19 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu, struct kvm_run *run)
        return 1;
 }
 
+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\n",
+                     hsr);
+
+       kvm_inject_undefined(vcpu);
+       return 1;
+}
+
 static exit_handle_fn arm_exit_handlers[] = {
+       [0 ... HSR_EC_MAX]      = kvm_handle_unknown_ec,
        [HSR_EC_WFI]            = kvm_handle_wfx,
        [HSR_EC_CP15_32]        = kvm_handle_cp15_32,
        [HSR_EC_CP15_64]        = kvm_handle_cp15_64,
@@ -98,13 +110,6 @@ static exit_handle_fn kvm_get_exit_handler(struct kvm_vcpu *vcpu)
 {
        u8 hsr_ec = kvm_vcpu_trap_get_class(vcpu);
 
-       if (hsr_ec >= ARRAY_SIZE(arm_exit_handlers) ||
-           !arm_exit_handlers[hsr_ec]) {
-               kvm_err("Unknown exception class: hsr: %#08x\n",
-                       (unsigned int)kvm_vcpu_get_hsr(vcpu));
-               BUG();
-       }
-
        return arm_exit_handlers[hsr_ec];
 }