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Commit f050fe7a authored by Mark Rutland's avatar Mark Rutland Committed by Marc Zyngier
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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: default avatarChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: default avatarMark Rutland <mark.rutland@arm.com>
Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
parent 370a0ec1

arch/arm/include/asm/kvm_arm.h

+1 −0
Original line number Diff line number Diff line
@@ -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)

arch/arm/kvm/handle_exit.c

+12 −7
Original line number Diff line number Diff line
@@ -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];

}