linux-kernel - [PATCH 5.15 037/110] KVM: arm64: Avoid consuming a stale esr value when SError occur

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Message-Id: <20220207103803.530037238@linuxfoundation.org>
Date:   Mon,  7 Feb 2022 12:06:10 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Steven Price <steven.price@....com>,
        James Morse <james.morse@....com>,
        Marc Zyngier <maz@...nel.org>
Subject: [PATCH 5.15 037/110] KVM: arm64: Avoid consuming a stale esr value when SError occur

From: James Morse <james.morse@....com>

commit 1c71dbc8a179d99dd9bb7e7fc1888db613cf85de upstream.

When any exception other than an IRQ occurs, the CPU updates the ESR_EL2
register with the exception syndrome. An SError may also become pending,
and will be synchronised by KVM. KVM notes the exception type, and whether
an SError was synchronised in exit_code.

When an exception other than an IRQ occurs, fixup_guest_exit() updates
vcpu->arch.fault.esr_el2 from the hardware register. When an SError was
synchronised, the vcpu esr value is used to determine if the exception
was due to an HVC. If so, ELR_EL2 is moved back one instruction. This
is so that KVM can process the SError first, and re-execute the HVC if
the guest survives the SError.

But if an IRQ synchronises an SError, the vcpu's esr value is stale.
If the previous non-IRQ exception was an HVC, KVM will corrupt ELR_EL2,
causing an unrelated guest instruction to be executed twice.

Check ARM_EXCEPTION_CODE() before messing with ELR_EL2, IRQs don't
update this register so don't need to check.

Fixes: defe21f49bc9 ("KVM: arm64: Move PC rollback on SError to HYP")
Cc: stable@...r.kernel.org
Reported-by: Steven Price <steven.price@....com>
Signed-off-by: James Morse <james.morse@....com>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Link: https://lore.kernel.org/r/20220127122052.1584324-3-james.morse@arm.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kvm/hyp/include/hyp/switch.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/arch/arm64/kvm/hyp/include/hyp/switch.h
+++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
@@ -425,7 +425,8 @@ static inline bool fixup_guest_exit(stru
 	if (ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ)
 		vcpu->arch.fault.esr_el2 = read_sysreg_el2(SYS_ESR);

-	if (ARM_SERROR_PENDING(*exit_code)) {
+	if (ARM_SERROR_PENDING(*exit_code) &&
+	    ARM_EXCEPTION_CODE(*exit_code) != ARM_EXCEPTION_IRQ) {
 		u8 esr_ec = kvm_vcpu_trap_get_class(vcpu);

 		/*