[PATCH v9 4/6] KVM: arm64: Validate the offset to the mem access descriptor

[Sebastian Ene]

Prevent the pKVM hypervisor from making assumptions that the
endpoint memory access descriptor (EMAD) comes right after the
FF-A memory region header.
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 from 1.1 onward:
Type | Field name | Offset
[ Header | ffa_mem_region  | 0
  EMAD 1 | ffa_mem_region_attributes) | ffa_mem_region.ep_mem_offset
]
Verify that the offset to the first endpoint memory access descriptor
is within the mailbox buffer bounds.

Also, fix one hardcoded sizeof(struct ffa_mem_region_attributes) that
should be replaced ffa_emad_size_get() for compatibility with FFA v1.0.

Fixes: 42fb33dde42b ("KVM: arm64: Use FF-A 1.1 with pKVM")
Signed-off-by: Mostafa Saleh <smostafa at google.com>
Signed-off-by: Sebastian Ene <sebastianene at google.com>
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 27 +++++++++++++++++++--------
 include/linux/arm_ffa.h       |  7 +++++++
 2 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 41cc4c1bafeb..2e7ab7e3319d 100644
--- a/arch/arm64/kvm/hyp/nvhe/ffa.c
+++ b/arch/arm64/kvm/hyp/nvhe/ffa.c
@@ -476,11 +476,12 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 	DECLARE_REG(u32, fraglen, ctxt, 2);
 	DECLARE_REG(u64, addr_mbz, ctxt, 3);
 	DECLARE_REG(u32, npages_mbz, ctxt, 4);
+	u32 offset, nr_ranges, checked_offset, em_mem_access_off;
 	struct ffa_mem_region_attributes *ep_mem_access;
 	struct ffa_composite_mem_region *reg;
 	struct ffa_mem_region *buf;
-	u32 offset, nr_ranges, checked_offset;
 	int ret = 0;
+	size_t mem_region_len = FFA_MEM_REGION_SZ(hyp_ffa_version);
 
 	if (addr_mbz || npages_mbz || fraglen > len ||
 	    fraglen > KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE) {
@@ -488,8 +489,7 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 		goto out;
 	}
 
-	if (fraglen < sizeof(struct ffa_mem_region) +
-		      sizeof(struct ffa_mem_region_attributes)) {
+	if (fraglen < mem_region_len + ffa_emad_size_get(hyp_ffa_version)) {
 		ret = FFA_RET_INVALID_PARAMETERS;
 		goto out;
 	}
@@ -508,8 +508,13 @@ static void __do_ffa_mem_xfer(const u64 func_id,
 	buf = hyp_buffers.tx;
 	memcpy(buf, host_buffers.tx, fraglen);
 
-	ep_mem_access = (void *)buf +
-			ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+	em_mem_access_off = ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+	if ((u64)em_mem_access_off + ffa_emad_size_get(hyp_ffa_version) > fraglen) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		goto out_unlock;
+	}
+
+	ep_mem_access = (void *)buf + em_mem_access_off;
 	offset = ep_mem_access->composite_off;
 	if (!offset || buf->ep_count != 1 || buf->sender_id != HOST_FFA_ID) {
 		ret = FFA_RET_INVALID_PARAMETERS;
@@ -574,9 +579,9 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
 	DECLARE_REG(u32, handle_lo, ctxt, 1);
 	DECLARE_REG(u32, handle_hi, ctxt, 2);
 	DECLARE_REG(u32, flags, ctxt, 3);
+	u32 offset, len, fraglen, fragoff, em_mem_access_off;
 	struct ffa_mem_region_attributes *ep_mem_access;
 	struct ffa_composite_mem_region *reg;
-	u32 offset, len, fraglen, fragoff;
 	struct ffa_mem_region *buf;
 	int ret = 0;
 	u64 handle;
@@ -599,8 +604,14 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
 	len = res->a1;
 	fraglen = res->a2;
 
-	ep_mem_access = (void *)buf +
-			ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+	em_mem_access_off = ffa_mem_desc_offset(buf, 0, hyp_ffa_version);
+	if ((u64)em_mem_access_off + ffa_emad_size_get(hyp_ffa_version) > fraglen) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		ffa_rx_release(res);
+		goto out_unlock;
+	}
+
+	ep_mem_access = (void *)buf + em_mem_access_off;
 	offset = ep_mem_access->composite_off;
 	/*
 	 * We can trust the SPMD to get this right, but let's at least
diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
index 033c630b271b..e71d83ee0aef 100644
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -421,6 +421,13 @@ struct ffa_mem_region {
 #define FFA_EMAD_HAS_IMPDEF_FIELD(version)	((version) >= FFA_VERSION_1_2)
 #define FFA_MEM_REGION_HAS_EP_MEM_OFFSET(version) ((version) > FFA_VERSION_1_0)
 
+/* The layout changed from FFA_VERSION_1_0 and the region includes an
+ * ep_mem_offset.
+ */
+#define FFA_MEM_REGION_SZ(version)		(!FFA_MEM_REGION_HAS_EP_MEM_OFFSET((version)) ?\
+						 offsetof(struct ffa_mem_region, ep_mem_offset) :\
+						 sizeof(struct ffa_mem_region))
+
 static inline u32 ffa_emad_size_get(u32 ffa_version)
 {
 	u32 sz;
-- 
2.55.0.rc0.799.gd6f94ed593-goog