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Subject[PATCH v4 2/7] KVM: arm64: Don't write to Rt unless sys_reg emulation succeeds
From
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;
}

/******************************************************************************
--
2.36.0.464.gb9c8b46e94-goog
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