[PATCH] KVM: arm64: Validate the FF-A memory access descriptor placement

[Sebastian Ene <sebastianene@google.com>]

Prevent the pKVM hypervisor from making assumptions that the
endpoint memory access descriptor (EMAD) comes right after the
FF-A memory region header and enforce a strict placement for it
when validating an FF-A memory lend/share transaction.

Prior to FF-A version 1.1 the header of the memory region
didn't contain an offset to the endpoint memory access descriptor.
The layout of a memory transaction looks like this:

  Field name				| Offset
					 -- 0
[ Header (ffa_mem_region)               |__ ep_mem_offset
  EMAD 1 (ffa_mem_region_attributes)	|
]

Reject the host from specifying a memory access descriptor offset
that is different than the size of the memory region header.

Cc: stable@vger.kernel.org
Fixes: 42fb33dde42b ("KVM: arm64: Use FF-A 1.1 with pKVM")
Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 94161ea1cd60..0703c0ad8dff 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -508,6 +508,12 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 	buf = hyp_buffers.tx;
 	memcpy(buf, host_buffers.tx, fraglen);
 
+	if (FFA_MEM_REGION_HAS_EP_MEM_OFFSET(hyp_ffa_version) &&
+	    buf->ep_mem_offset != sizeof(struct ffa_mem_region)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out_unlock;
+	}
+
 	ep_mem_access = (void *)buf +
 			ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
 	offset = ep_mem_access->composite_off;
-- 
2.54.0.rc1.555.g9c883467ad-goog