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From: Oliver Upton <oupton@google.com>
To: kvmarm@lists.cs.columbia.edu
Cc: kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	 linux-kernel@vger.kernel.org, maz@kernel.org,
	james.morse@arm.com,  alexandru.elisei@arm.com,
	suzuki.poulose@arm.com, reijiw@google.com,  ricarkol@google.com,
	Oliver Upton <oupton@google.com>
Subject: [PATCH v3 2/5] KVM: arm64: Don't write to Rt unless sys_reg emulation succeeds
Date: Mon, 25 Apr 2022 23:53:39 +0000	[thread overview]
Message-ID: <20220425235342.3210912-3-oupton@google.com> (raw)
In-Reply-To: <20220425235342.3210912-1-oupton@google.com>

emulate_sys_reg() returns 1 unconditionally, even though a a system
register access can fail. Furthermore, kvm_handle_sys_reg() writes to Rt
for every register read, regardless of if it actually succeeded.

Though this pattern is safe (as params.regval is initialized with the
current value of Rt) it is a bit ugly. Indicate failure if the register
access could not be emulated and only write to Rt on success.

Signed-off-by: Oliver Upton <oupton@google.com>
---
 arch/arm64/kvm/sys_regs.c | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 36895c163eae..f0a076e5cc1c 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -2401,7 +2401,14 @@ static bool is_imp_def_sys_reg(struct sys_reg_params *params)
 	return params->Op0 == 3 && (params->CRn & 0b1011) == 0b1011;
 }
 
-static int emulate_sys_reg(struct kvm_vcpu *vcpu,
+/**
+ * emulate_sys_reg - Emulate a guest access to an AArch64 system register
+ * @vcpu: The VCPU pointer
+ * @params: Decoded system register parameters
+ *
+ * Return: true if the system register access was successful, false otherwise.
+ */
+static bool emulate_sys_reg(struct kvm_vcpu *vcpu,
 			   struct sys_reg_params *params)
 {
 	const struct sys_reg_desc *r;
@@ -2410,7 +2417,10 @@ static int emulate_sys_reg(struct kvm_vcpu *vcpu,
 
 	if (likely(r)) {
 		perform_access(vcpu, params, r);
-	} else if (is_imp_def_sys_reg(params)) {
+		return true;
+	}
+
+	if (is_imp_def_sys_reg(params)) {
 		kvm_inject_undefined(vcpu);
 	} else {
 		print_sys_reg_msg(params,
@@ -2418,7 +2428,7 @@ static int emulate_sys_reg(struct kvm_vcpu *vcpu,
 				  *vcpu_pc(vcpu), *vcpu_cpsr(vcpu));
 		kvm_inject_undefined(vcpu);
 	}
-	return 1;
+	return false;
 }
 
 /**
@@ -2446,18 +2456,18 @@ int kvm_handle_sys_reg(struct kvm_vcpu *vcpu)
 	struct sys_reg_params params;
 	unsigned long esr = kvm_vcpu_get_esr(vcpu);
 	int Rt = kvm_vcpu_sys_get_rt(vcpu);
-	int ret;
 
 	trace_kvm_handle_sys_reg(esr);
 
 	params = esr_sys64_to_params(esr);
 	params.regval = vcpu_get_reg(vcpu, Rt);
 
-	ret = emulate_sys_reg(vcpu, &params);
+	if (!emulate_sys_reg(vcpu, &params))
+		return 1;
 
 	if (!params.is_write)
 		vcpu_set_reg(vcpu, Rt, params.regval);
-	return ret;
+	return 1;
 }
 
 /******************************************************************************
-- 
2.36.0.rc2.479.g8af0fa9b8e-goog


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  parent reply	other threads:[~2022-04-25 23:55 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-04-25 23:53 [PATCH v3 0/5] KVM: arm64: Limit feature register reads from AArch32 Oliver Upton
2022-04-25 23:53 ` [PATCH v3 1/5] KVM: arm64: Return a bool from emulate_cp() Oliver Upton
2022-04-25 23:53 ` Oliver Upton [this message]
2022-04-25 23:53 ` [PATCH v3 3/5] KVM: arm64: Wire up CP15 feature registers to their AArch64 equivalents Oliver Upton
2022-04-25 23:53 ` [PATCH v3 4/5] KVM: arm64: Plumb cp10 ID traps through the AArch64 sysreg handler Oliver Upton
2022-04-25 23:53 ` [PATCH v3 5/5] KVM: arm64: Start trapping ID registers for 32 bit guests Oliver Upton
2022-04-26  9:15 ` [PATCH v3 0/5] KVM: arm64: Limit feature register reads from AArch32 Alexandru Elisei

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