Execute "SMC" instruction in Guest OS

Execute "SMC" instruction in Guest OS

[Chenxu Wang]

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Hi all,

I want the Guest OS to use the Arm-TF service in Host OS (It is the same as
using Trusted Application in OP-TEE). So I should provide some parameters
and call SMC instruction.

But it returns an "Undefined Instruction" in my Linux v4.9.51.
I find that KVM calls a " kvm_inject_undefined(vcpu);" when handling the
SMC instruction.

So, if I want the Guest OS to use the "Arm-TF service" or "TA", should I
simply change the kvm_inject_undefined() as "SMC #0", and carefully handle
the input parameters? What else should I do?

Sincerely,
Wang Chenxu

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Re: Execute "SMC" instruction in Guest OS

[Marc Zyngier]

Hi Chenxu,

On 2021-09-25 07:45, Chenxu Wang wrote:
> Hi all,
> 
> I want the Guest OS to use the Arm-TF service in Host OS (It is the
> same as using Trusted Application in OP-TEE). So I should provide some
> parameters and call SMC instruction.

It is unlikely to work out of the box. For a start, the guest is a
different entity altogether, and it is unlikely that ATF can directly
deal with a request coming from the guest, specially if you are passing
any sort of memory reference.

> But it returns an "Undefined Instruction" in my Linux v4.9.51.
> I find that KVM calls a " kvm_inject_undefined(vcpu);" when handling
> the SMC instruction.

You should really get rid of this kernel and move to something more
recent. This UNDEF injection is a bug which has been fixed in more
recent versions of the kernel (by returning -1 instead).

> So, if I want the Guest OS to use the "Arm-TF service" or "TA", should
> I simply change the kvm_inject_undefined() as "SMC #0", and carefully
> handle the input parameters? What else should I do?

You should probably consider relaying the SMC to userspace, and then get
the VMM to do the talking with with the platform TEE driver.

         M.
-- 
Who you jivin' with that Cosmik Debris?
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