[PATCH] KVM: arm64: Check the untrusted offset in FF-A memory share

[Sebastian Ene <sebastianene@google.com>]

Verify the offset to prevent OOB access in the hypervisor
FF-A buffer in case an untrusted large enough value
[U32_MAX - sizeof(struct ffa_composite_mem_region) + 1, U32_MAX]
is set from the host kernel.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 4e16f9b96f63..58b7d0c477d7 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -479,7 +479,7 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 	struct ffa_mem_region_attributes *ep_mem_access;
 	struct ffa_composite_mem_region *reg;
 	struct ffa_mem_region *buf;
-	u32 offset, nr_ranges;
+	u32 offset, nr_ranges, checked_offset;
 	int ret = 0;
 
 	if (addr_mbz || npages_mbz || fraglen > len ||
@@ -516,7 +516,12 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 		goto out_unlock;
 	}
 
-	if (fraglen < offset + sizeof(struct ffa_composite_mem_region)) {
+	if (check_add_overflow(offset, sizeof(struct ffa_composite_mem_region), &checked_offset)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out_unlock;
+	}
+
+	if (fraglen < checked_offset) {
 		ret = FFA_RET_INVALID_PARAMETERS;
 		goto out_unlock;
 	}
-- 
2.51.0.858.gf9c4a03a3a-goog