[PATCH v2 7/9] arm64: KVM: Do not corrupt registers on failed 64bit CP read

Marc Zyngier
2017-03-27T16:02:11Z

If we fail to emulate a mrrc instruction, we:
1) deliver an exception,
2) spit a nastygram on the console,
3) write back some garbage to Rt/Rt2

While 1) and 2) are perfectly acceptable, 3) is out of the scope of
the architecture... Let's mimick the code in kvm_handle_cp_32 and
be more cautious.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
---
arch/arm64/kvm/sys_regs.c | 20 +++++++++-----------
1 file changed, 9 insertions(+), 11 deletions(-)

diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
index 4e5d4eee8cec..1080a76e960f 100644
--- a/arch/arm64/kvm/sys_regs.c
+++ b/arch/arm64/kvm/sys_regs.c
@@ -1678,20 +1678,18 @@ static int kvm_handle_cp_64(struct kvm_vcpu *vcpu,
params.regval |= vcpu_get_reg(vcpu, Rt2) << 32;
}

- if (!emulate_cp(vcpu, &params, target_specific, nr_specific))
- goto out;
- if (!emulate_cp(vcpu, &params, global, nr_global))
- goto out;
-
- unhandled_cp_access(vcpu, &params);
+ if (!emulate_cp(vcpu, &params, target_specific, nr_specific) ||
+ !emulate_cp(vcpu, &params, global, nr_global)) {
+ /* Split up the value between registers for the read side */
+ if (!params.is_write) {
+ vcpu_set_reg(vcpu, Rt, lower_32_bits(params.regval));
+ vcpu_set_reg(vcpu, Rt2, upper_32_bits(params.regval));
+ }

-out:
- /* Split up the value between registers for the read side */
- if (!params.is_write) {
- vcpu_set_reg(vcpu, Rt, lower_32_bits(params.regval));
- vcpu_set_reg(vcpu, Rt2, upper_32_bits(params.regval));
+ return 1;
}

+ unhandled_cp_access(vcpu, &params);
return 1;
}

--
2.11.0