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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>
This commit is contained in:
Mark Rutland 2017-02-20 12:30:11 +00:00 committed by Marc Zyngier
parent 370a0ec181
commit f050fe7a91
2 changed files with 13 additions and 7 deletions
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1
arch/arm/include/asm/kvm_arm.h
View File

@ -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)

19
arch/arm/kvm/handle_exit.c
View File

@ -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];
}