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

[Marc Zyngier]

On 28/03/17 13:46, Christoffer Dall wrote:
> On Mon, Mar 27, 2017 at 05:03:43PM +0100, Marc Zyngier wrote:
>> 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 
>> ---
>>  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, , target_specific, nr_specific))
>> -goto out;
>> -if (!emulate_cp(vcpu, , global, nr_global))
>> -goto out;
>> -
>> -unhandled_cp_access(vcpu, );
>> +if (!emulate_cp(vcpu, , target_specific, nr_specific) ||
>> +!emulate_cp(vcpu, , global, nr_global)) {
> 
> super nit: I choked a bit on this contruct, any objections to adding a
> comment like the following above:
> 
>   /*
>* Try to emulate the coprocessor access using the target
>* specific table first, and using the global table aftwards.
>* If either of the tables contains a handler, handle the
>* potential register operation in the case of a read and return
>* with success.
>*/
> 
> Too much?
> 
> (If not, I can also add this when applying).

No, that's great. Thanks!

M.
-- 
Jazz is not dead. It just smells funny...
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[PATCH v2 7/9] arm64: KVM: Do not corrupt registers on failed 64bit CP read

[Marc Zyngier]

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 
---
 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, , target_specific, nr_specific))
-   goto out;
-   if (!emulate_cp(vcpu, , global, nr_global))
-   goto out;
-
-   unhandled_cp_access(vcpu, );
+   if (!emulate_cp(vcpu, , target_specific, nr_specific) ||
+   !emulate_cp(vcpu, , 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, );
return 1;
 }
 
-- 
2.11.0

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