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

Marc Zyngier
2017-03-28T13:22:58Z

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 <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)) {
>
> 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...