KVM: arm64: Add memory length checks and remove inline in do_ffa_mem_xfer

When we share memory through FF-A and the description of the buffers
exceeds the size of the mapped buffer, the fragmentation API is used.
The fragmentation API allows specifying chunks of descriptors in subsequent
FF-A fragment calls and no upper limit has been established for this.
The entire memory region transferred is identified by a handle which can be
used to reclaim the transferred memory.
To be able to reclaim the memory, the description of the buffers has to fit
in the ffa_desc_buf.
Add a bounds check on the FF-A sharing path to prevent the memory reclaim
from failing.

Also do_ffa_mem_xfer() does not need __always_inline, except for the
BUILD_BUG_ON() aspect, which gets moved to a macro.

[maz: fixed the BUILD_BUG_ON() breakage with LLVM, thanks to Wei-Lin Chang
 for the timely report]

Fixes: 634d90c ("KVM: arm64: Handle FFA_MEM_LEND calls from the host")
Cc: stable@vger.kernel.org
Reviewed-by: Sebastian Ene <sebastianene@google.com>
Signed-off-by: Snehal Koukuntla <snehalreddy@google.com>
Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20240909180154.3267939-1-snehalreddy@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Snehal-Reddy

arch/arm64/kvm/hyp/nvhe/ffa.c

@@ -426,9 +426,9 @@ static void do_ffa_mem_frag_tx(struct arm_smccc_res *res,
 	return;
 }
 
-static __always_inline void do_ffa_mem_xfer(const u64 func_id,
-					    struct arm_smccc_res *res,
-					    struct kvm_cpu_context *ctxt)
+static void __do_ffa_mem_xfer(const u64 func_id,
+			      struct arm_smccc_res *res,
+			      struct kvm_cpu_context *ctxt)
 {
 	DECLARE_REG(u32, len, ctxt, 1);
 	DECLARE_REG(u32, fraglen, ctxt, 2);
@@ -440,9 +440,6 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
 	u32 offset, nr_ranges;
 	int ret = 0;
 
-	BUILD_BUG_ON(func_id != FFA_FN64_MEM_SHARE &&
-		     func_id != FFA_FN64_MEM_LEND);
-
 	if (addr_mbz || npages_mbz || fraglen > len ||
 	    fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
 		ret = FFA_RET_INVALID_PARAMETERS;
@@ -461,6 +458,11 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
 		goto out_unlock;
 	}
 
+	if (len > ffa_desc_buf.len) {
+		ret = FFA_RET_NO_MEMORY;
+		goto out_unlock;
+	}
+
 	buf = hyp_buffers.tx;
 	memcpy(buf, host_buffers.tx, fraglen);
 
@@ -512,6 +514,13 @@ static __always_inline void do_ffa_mem_xfer(const u64 func_id,
 	goto out_unlock;
 }
 
+#define do_ffa_mem_xfer(fid, res, ctxt)				\
+	do {							\
+		BUILD_BUG_ON((fid) != FFA_FN64_MEM_SHARE &&	\
+			     (fid) != FFA_FN64_MEM_LEND);	\
+		__do_ffa_mem_xfer((fid), (res), (ctxt));	\
+	} while (0);
+
 static void do_ffa_mem_reclaim(struct arm_smccc_res *res,
 			       struct kvm_cpu_context *ctxt)
 {