[PATCH v2 0/2] arm_ffa, KVM: Fix FF-A emad offset calculations

[PATCH v2 0/2] arm_ffa, KVM: Fix FF-A emad offset calculations

[Sebastian Ene]

Hi all,

This series fixes the Endpoint Memory Access Descriptor (EMAD) offset calculations
and adds the necessary bounds checks for both the core FF-A driver and the pKVM
hypervisor.

Prior to FF-A version 1.1, the memory region header didn't specify an explicit offset
for the EMADs, leading to the assumption that they immediately follow the header.
However, from v1.1 onwards, the specification dictates using the `ep_mem_offset` field
to determine the start of the memory access array.

The patches in this series address this by:
1. Updating the core `arm_ffa` firmware driver to correctly calculate the descriptor
   offset using `ep_mem_offset` rather than defaulting to `sizeof(struct ffa_mem_region)`.
   It also introduces bounds checking against `max_fragsize`.
2. Enhancing the pKVM hypervisor validation logic to no longer strictly enforce that
   the descriptor strictly follows the header, aligning it with the driver behavior
   and the FF-A specification, while also ensuring the offset falls within the mailbox
   buffer bounds.

Changes since v1:
- For pKVM, removed the strict placement enforcement for `ep_mem_offset` as it is not
  compliant with the spec, and avoids making assumptions about the driver's memory
  layout.

Link to v1: https://lore.kernel.org/all/ae9KN9nkOgDYJcGP@google.com/T/#t

Sebastian Ene (2):
  firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset
    calculation
  KVM: arm64: Validate the offset to the mem access descriptor

 arch/arm64/kvm/hyp/nvhe/ffa.c     | 24 ++++++++++++++++++------
 drivers/firmware/arm_ffa/driver.c | 14 ++++++++++----
 include/linux/arm_ffa.h           |  2 +-
 3 files changed, 29 insertions(+), 11 deletions(-)

--
2.54.0.545.g6539524ca2-goog

[PATCH v2 1/2] firmware: arm_ffa: Fix Endpoint Memory Access Descriptor offset calculation

[Sebastian Ene]

Use the descriptor's `ep_mem_offset` to calculate the start of the endpoint
memory access array and to comply with the FF-A spec instead of defaulting
to `sizeof(struct ffa_mem_region)`.
This requires moving `ffa_mem_region_additional_setup()` earlier in the setup
flow.
Also, add sanity checks to ensure the calculated descriptor offsets do not
exceed `max_fragsize`.

Signed-off-by: Sebastian Ene <sebastianene@google.com>
---
 drivers/firmware/arm_ffa/driver.c | 14 ++++++++++----
 include/linux/arm_ffa.h           |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/firmware/arm_ffa/driver.c b/drivers/firmware/arm_ffa/driver.c
index eb2782848283..56b166290b24 100644
--- a/drivers/firmware/arm_ffa/driver.c
+++ b/drivers/firmware/arm_ffa/driver.c
@@ -685,18 +685,25 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize,
 	struct ffa_composite_mem_region *composite;
 	struct ffa_mem_region_addr_range *constituents;
 	struct ffa_mem_region_attributes *ep_mem_access;
-	u32 idx, frag_len, length, buf_sz = 0, num_entries = sg_nents(args->sg);
+	u32 idx, frag_len, length, buf_sz = 0, num_entries = sg_nents(args->sg), ep_offset;
 
 	mem_region->tag = args->tag;
 	mem_region->flags = args->flags;
 	mem_region->sender_id = drv_info->vm_id;
 	mem_region->attributes = ffa_memory_attributes_get(func_id);
+
+	ffa_mem_region_additional_setup(drv_info->version, mem_region);
 	composite_offset = ffa_mem_desc_offset(buffer, args->nattrs,
 					       drv_info->version);
+	if (composite_offset > max_fragsize - sizeof(struct ffa_composite_mem_region))
+		return -ENXIO;
 
 	for (idx = 0; idx < args->nattrs; idx++) {
-		ep_mem_access = buffer +
-			ffa_mem_desc_offset(buffer, idx, drv_info->version);
+		ep_offset = ffa_mem_desc_offset(buffer, idx, drv_info->version);
+		if (ep_offset > max_fragsize - sizeof(struct ffa_mem_region_attributes))
+			return -ENXIO;
+
+		ep_mem_access = buffer + ep_offset;
 		ep_mem_access->receiver = args->attrs[idx].receiver;
 		ep_mem_access->attrs = args->attrs[idx].attrs;
 		ep_mem_access->composite_off = composite_offset;
@@ -708,7 +715,6 @@ ffa_setup_and_transmit(u32 func_id, void *buffer, u32 max_fragsize,
 	}
 	mem_region->handle = 0;
 	mem_region->ep_count = args->nattrs;
-	ffa_mem_region_additional_setup(drv_info->version, mem_region);
 
 	composite = buffer + composite_offset;
 	composite->total_pg_cnt = ffa_get_num_pages_sg(args->sg);
diff --git a/include/linux/arm_ffa.h b/include/linux/arm_ffa.h
index 81e603839c4a..62d67dae8b70 100644
--- a/include/linux/arm_ffa.h
+++ b/include/linux/arm_ffa.h
@@ -445,7 +445,7 @@ ffa_mem_desc_offset(struct ffa_mem_region *buf, int count, u32 ffa_version)
 	if (!FFA_MEM_REGION_HAS_EP_MEM_OFFSET(ffa_version))
 		offset += offsetof(struct ffa_mem_region, ep_mem_offset);
 	else
-		offset += sizeof(struct ffa_mem_region);
+		offset += buf->ep_mem_offset;
 
 	return offset;
 }
-- 
2.54.0.545.g6539524ca2-goog

[PATCH v2 2/2] 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.

Signed-off-by: Sebastian Ene <sebastianene@google.com>

---
v1 -> v2:
 * don't enforce a strict placement for the ep_mem_offset since this is
   not compliant with the spec and we should not make assumptions about
   the driver.

Link to v1: https://lore.kernel.org/all/ae9KN9nkOgDYJcGP@google.com/T/#t

---
---
 arch/arm64/kvm/hyp/nvhe/ffa.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/ffa.c b/arch/arm64/kvm/hyp/nvhe/ffa.c
index 1af722771178..8e9017fc8e39 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, checked_offset;
+	u32 offset, nr_ranges, checked_offset, em_mem_access_off;
 	int ret = 0;
 
 	if (addr_mbz || npages_mbz || fraglen > len ||
@@ -508,8 +508,14 @@ 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 (em_mem_access_off >
+	    KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE - (struct ffa_mem_region_attributes)) {
+		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;
@@ -576,7 +582,7 @@ static void do_ffa_mem_reclaim(struct arm_smccc_1_2_regs *res,
 	DECLARE_REG(u32, flags, ctxt, 3);
 	struct ffa_mem_region_attributes *ep_mem_access;
 	struct ffa_composite_mem_region *reg;
-	u32 offset, len, fraglen, fragoff;
+	u32 offset, len, fraglen, fragoff, em_mem_access_off;
 	struct ffa_mem_region *buf;
 	int ret = 0;
 	u64 handle;
@@ -599,8 +605,14 @@ 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 (em_mem_access_off >
+	    KVM_FFA_MBOX_NR_PAGES * PAGE_SIZE - (struct ffa_mem_region_attributes)) {
+		ret = FFA_RET_INVALID_PARAMETERS;
+		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
-- 
2.54.0.545.g6539524ca2-goog