Sorry, hit send a bit too early. Reviewing the patch itself:
On Wed, Nov 16, 2022 at 05:03:26PM +0000, Quentin Perret wrote:
[...]
> +static bool ffa_call_unsupported(u64 func_id)
> +{
> + switch (func_id) {
> + /* Unsupported memory management calls */
> + case FFA_FN64_MEM_RETRIEVE_REQ:
> + case FFA_MEM_RETRIEVE_RESP:
> + case FFA_MEM_RELINQUISH:
> + case FFA_MEM_OP_PAUSE:
> + case FFA_MEM_OP_RESUME:
> + case FFA_MEM_FRAG_RX:
> + case FFA_FN64_MEM_DONATE:
> + /* Indirect message passing via RX/TX buffers */
> + case FFA_MSG_SEND:
> + case FFA_MSG_POLL:
> + case FFA_MSG_WAIT:
> + /* 32-bit variants of 64-bit calls */
> + case FFA_MSG_SEND_DIRECT_REQ:
> + case FFA_MSG_SEND_DIRECT_RESP:
> + case FFA_RXTX_MAP:
> + case FFA_MEM_DONATE:
> + case FFA_MEM_RETRIEVE_REQ:
> + return true;
> + }
> +
> + return false;
> +}
Wouldn't an allowlist behave better in this case? While unlikely, you
wouldn't want EL3 implementing some FFA_BACKDOOR_PVM SMC that falls
outside of the denylist and is passed through.
> +bool kvm_host_ffa_handler(struct kvm_cpu_context *host_ctxt)
> +{
> + DECLARE_REG(u64, func_id, host_ctxt, 0);
> + struct arm_smccc_res res;
> +
> + if (!is_ffa_call(func_id))
> + return false;
> +
> + switch (func_id) {
> + /* Memory management */
> + case FFA_FN64_RXTX_MAP:
> + case FFA_RXTX_UNMAP:
> + case FFA_MEM_SHARE:
> + case FFA_FN64_MEM_SHARE:
> + case FFA_MEM_LEND:
> + case FFA_FN64_MEM_LEND:
> + case FFA_MEM_RECLAIM:
> + case FFA_MEM_FRAG_TX:
> + break;
> + }
What is the purpose of this switch?
> +
> + if (!ffa_call_unsupported(func_id))
> + return false; /* Pass through */
Another (tiny) benefit of implementing an allowlist is that it avoids
the use of double-negative logic like this.
--
Thanks,
Oliver
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