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Subject[PATCH 4.9 094/148] arm: KVM: Survive unknown traps from guests
Date
4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Mark Rutland <mark.rutland@arm.com>


[ Upstream commit f050fe7a9164945dd1c28be05bf00e8cfb082ccf ]

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>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/arm/include/asm/kvm_arm.h | 1 +
arch/arm/kvm/handle_exit.c | 19 ++++++++++++-------
2 files changed, 13 insertions(+), 7 deletions(-)

--- a/arch/arm/include/asm/kvm_arm.h
+++ b/arch/arm/include/asm/kvm_arm.h
@@ -208,6 +208,7 @@
#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)

--- 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_vcp
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_handl
{
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];
}


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