[PATCH 4/4] accel/amdxdna: check the command payload before using it in the exec requests

[Eva Crystal <0xiviel@gmail.com>]

aie2_init_exec_dpu_req() takes the payload of a command BO and subtracts
the fixed header from its length before establishing that the length
covers the header at all:

	sn = amdxdna_cmd_get_payload(cmd_bo, &cmd_len);
	if (cmd_len - sizeof(*sn) > sizeof(dpu_req->payload))
		return -EINVAL;
	...
	dpu_req->inst_buf_addr = sn->buffer;
	memcpy(dpu_req->payload, sn->prop_args, cmd_len - sizeof(*sn));

It also dereferences sn without testing it, although
amdxdna_cmd_get_payload() returns NULL for a command header whose count
field does not fit the BO, setting cmd_len to 0 as it does so.

Both work out today, and for the same reason: cmd_len is a u32 and
sizeof() is a size_t, so the subtraction is evaluated in 64-bit. A short
command produces a value near 2^64, which is larger than the payload
field, so the test returns -EINVAL before sn is dereferenced and before
the memcpy. The NULL case is caught by the same comparison, because
cmd_len is then 0.

The guarantee is therefore supplied entirely by the operand types. A
later change that computes the difference into a u32 first - as the
sibling slot-filling functions in this file already do - would truncate
the underflow to a small value, and the function would dereference NULL
and copy from a short payload. Those siblings, aie2_cmdlist_fill_dpu()
and friends, all carry an explicit "cmd_len < sizeof(*sn)" test for
exactly this reason; this path was left without one.

Add the explicit length and NULL tests here, matching the siblings, and
add the missing NULL test to aie2_init_exec_cu_req(), which copies
cmd_len bytes from a pointer it likewise never checks. No behavioural
change is intended: every input rejected by the new tests is already
rejected today.

Signed-off-by: Eva Crystal <0xiviel@gmail.com>
---
 drivers/accel/amdxdna/aie2_message.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/accel/amdxdna/aie2_message.c b/drivers/accel/amdxdna/aie2_message.c
index 3028968..ab9e7c4 100644
--- a/drivers/accel/amdxdna/aie2_message.c
+++ b/drivers/accel/amdxdna/aie2_message.c
@@ -556,7 +556,7 @@ static int aie2_init_exec_cu_req(struct amdxdna_gem_obj *cmd_bo, void *req,
 	void *cmd;
 
 	cmd = amdxdna_cmd_get_payload(cmd_bo, &cmd_len);
-	if (cmd_len > sizeof(cu_req->payload))
+	if (!cmd || cmd_len > sizeof(cu_req->payload))
 		return -EINVAL;
 
 	cu_req->cu_idx = amdxdna_cmd_get_cu_idx(cmd_bo);
@@ -578,7 +578,8 @@ static int aie2_init_exec_dpu_req(struct amdxdna_gem_obj *cmd_bo, void *req,
 	u32 cmd_len;
 
 	sn = amdxdna_cmd_get_payload(cmd_bo, &cmd_len);
-	if (cmd_len - sizeof(*sn) > sizeof(dpu_req->payload))
+	if (!sn || cmd_len < sizeof(*sn) ||
+	    cmd_len - sizeof(*sn) > sizeof(dpu_req->payload))
 		return -EINVAL;
 
 	dpu_req->cu_idx = amdxdna_cmd_get_cu_idx(cmd_bo);
-- 
2.53.0