Re: [PATCH 2/4] KVM: arm64: Add support for FFA_PARTITION_INFO_GET

[Sebastian Ene <sebastianene@google.com>]

On Fri, May 03, 2024 at 04:01:16PM +0100, Will Deacon wrote:
> On Thu, Apr 18, 2024 at 04:30:24PM +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@google.com>
> > ---
> >  arch/arm64/kvm/hyp/nvhe/ffa.c | 46 +++++++++++++++++++++++++++++++++++
> >  1 file changed, 46 insertions(+)
> > 
> > diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > index 023712e8beeb..d53f50c73acb 100644
> > --- a/arch/arm64/kvm/hyp/nvhe/ffa.c
> > +++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
> > @@ -674,6 +674,49 @@ static void do_ffa_version(struct arm_smccc_res *res,
> >  	hyp_spin_unlock(&host_buffers.lock);
> >  }

Hello Will,

> >  
> > +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);
> 
> This should be FFA_RET_BUSY per the spec.
> 

Good catch, thank you ! I am fixing this.

> > +		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;
> > +
> > +	if (host_buffers.ffa_version > FFA_VERSION_1_0) {
> 
> The spec says that the size field is populated based on the flags
> parameter. Why aren't you checking that instead of the version number?
>

Right but the flags were introduced in the latest version (they were not
in 1.0). In 1.0 the content of w5 is reserved and this is why I need the
version check.

> > +		buf_sz = sz = res->a3;
> > +		if (sz > sizeof(struct ffa_partition_info))
> > +			buf_sz = sizeof(struct ffa_partition_info);
> 
> I don't think this is right, as if the payload really is bigger than
> 'struct ffa_partition_info' we'll truncate the data (and you don't
> adjust res->a3 afaict).
> 
> Can't we just copy the whole thing back to the host? We're not
> interpreting the thing, so we can just treat it like a stream of bytes.
>

Let me rewrite this. You are right, we should treat it like a stream of
bytes.

> > +	} else {
> > +		/* FFA_VERSION_1_0 lacks the size in the response */
> > +		buf_sz = sz = 8;
> 
> Can you define that as a constant in arm_ffa.h, please? It's the size of
> a 1.0 partition info structure.
> 

Yup, I am adding this.

> > +	}
> > +
> > +	WARN_ON((count - 1) * sz + buf_sz > PAGE_SIZE);
> 
> We should bounds-check against 'KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE' and
> return an error (FFA_RET_ABORTED) if the size is over that.
> 

Thanks, this should work I will do this.

> > +	for (off = 0; off < count * sz; off += sz)
> > +
> > +		memcpy(host_buffers.rx + off, hyp_buffers.rx + off, buf_sz);
> 
> I think this is wrong if bit 0 of 'flags' is set to 1. In that case, I
> think you just get back the number of partitions and that's it, so we
> shouldn't be going near the mailboxes.
> 

I removed this, thanks for the review !

> Will