Re: [PATCH] KVM: arm64: Add support for FFA_PARTITION_INFO_GET

[Sebastian Ene]

On Tue, Apr 09, 2024 at 05:15:20PM +0100, Vincent Donnefort wrote:
> Hi Seb,
> 
> On Tue, Apr 09, 2024 at 03:19:08PM +0000, Sebastian Ene wrote:
> > Handle the FFA_PARTITION_INFO_GET host call inside the pKVM hypervisor
> > and copy the response message back to the host buffers. Save the
> > returned FF-A version as we will need it later to interpret the response
> > from the TEE.
> > 
> > Signed-off-by: Sebastian Ene <sebastianene@xxxxxxxxxx>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/ffa.c | 49 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 49 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > index 320f2eaa14a9..72fc365bc7a8 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > @@ -67,6 +67,7 @@ struct kvm_ffa_buffers {
> >   */
> >  static struct kvm_ffa_buffers hyp_buffers;
> >  static struct kvm_ffa_buffers host_buffers;
> > +static u32 ffa_version;
> >  
> >  static void ffa_to_smccc_error(struct arm_smccc_res *res, u64 ffa_errno)
> >  {
> > @@ -640,6 +641,49 @@ static bool do_ffa_features(struct arm_smccc_res *res,
> >  	return true;
> >  }
> >  
> > +static void do_ffa_part_get(struct arm_smccc_res *res,
> > +			    struct kvm_cpu_context *ctxt)
> > +{
> > +	DECLARE_REG(u32, uuid0, ctxt, 1);
> > +	DECLARE_REG(u32, uuid1, ctxt, 2);
> > +	DECLARE_REG(u32, uuid2, ctxt, 3);
> > +	DECLARE_REG(u32, uuid3, ctxt, 4);
> > +	DECLARE_REG(u32, flags, ctxt, 5);
> > +	u32 off, count, sz, buf_sz;
> > +
> > +	hyp_spin_lock(&host_buffers.lock);
> > +	if (!host_buffers.rx) {
> > +		ffa_to_smccc_res(res, FFA_RET_INVALID_PARAMETERS);
> > +		goto out_unlock;
> > +	}
> > +
> > +	arm_smccc_1_1_smc(FFA_PARTITION_INFO_GET, uuid0, uuid1,
> > +			  uuid2, uuid3, flags, 0, 0,
> > +			  res);
> > +
> > +	if (res->a0 != FFA_SUCCESS)
> > +		goto out_unlock;
> > +
> > +	count = res->a2;
> > +	if (!count)
> > +		goto out_unlock;
> 
> Looking at the table 13.34, it seems what's in "count" depends on the flag.
> Shouldn't we check its value, and only memcpy into the host buffers if the flag
> is 0?
> 

When the flag is `1` the count referes to the number of partitions
deployed. In both cases we have to copy something unless count == 0.

> > +
> > +	if (ffa_version > FFA_VERSION_1_0) {
> > +		buf_sz = sz = res->a3;
> > +		if (sz > sizeof(struct ffa_partition_info))
> > +			buf_sz = sizeof(struct ffa_partition_info);
> 
> What are you trying to protect against here? We have to trust EL3 anyway, (as
> other functions do).
> 
> The WARN() could be kept though to make sure we won't overflow our buffer. But
> it could be transformed into an error? FFA_RET_ABORTED?
> 
>

I think we can keep it as a WARN_ON because it is not expected to have
a return code of FFA_SUCCESS but the buffer to be overflown. The TEE is
expected to return NO_MEMORY in w2 if the results cannot fit in the RX
buffer.

Thanks,
Seb

> > +	} else {
> > +		/* FFA_VERSION_1_0 lacks the size in the response */
> > +		buf_sz = sz = 8;
> > +	}
> > +
> > +	WARN_ON((count - 1) * sz + buf_sz > PAGE_SIZE);
> > +	for (off = 0; off < count * sz; off += sz)
> > +		memcpy(host_buffers.rx + off, hyp_buffers.rx + off, buf_sz);
> > +out_unlock:
> > +	hyp_spin_unlock(&host_buffers.lock);
> > +}
> > +
> >  bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
> >  {
> >  	struct arm_smccc_res res;
> > @@ -686,6 +730,9 @@ bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt, u32 func_id)
> >  	case FFA_MEM_FRAG_TX:
> >  		do_ffa_mem_frag_tx(&res, host_ctxt);
> >  		goto out_handled;
> > +	case FFA_PARTITION_INFO_GET:
> > +		do_ffa_part_get(&res, host_ctxt);
> > +		break;
> >  	}
> >  
> >  	if (ffa_call_supported(func_id))
> > @@ -726,6 +773,8 @@ int hyp_ffa_init(void *pages)
> >  	if (FFA_MAJOR_VERSION(res.a0) != 1)
> >  		return -EOPNOTSUPP;
> >  
> > +	ffa_version = res.a0;
> > +
> >  	arm_smccc_1_1_smc(FFA_ID_GET, 0, 0, 0, 0, 0, 0, 0, &res);
> >  	if (res.a0 != FFA_SUCCESS)
> >  		return -EOPNOTSUPP;
> > -- 
> > 2.44.0.478.gd926399ef9-goog
> >