platform/x86/amd/pmf: Fix possible out-of-bound memory accesses

The length of the policy buffer is not validated before accessing it,
which means that multiple out-of-bounds memory accesses can occur.

This is especially bad since userspace can load policy binaries over
debugfs.

Compile-tested only.

Fixes: 7c45534a ("platform/x86/amd/pmf: Add support for PMF Policy Binary")
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Shyam Sundar S K <Shyam-sundar.S-k@amd.com>
Link: https://lore.kernel.org/r/20240304205005.10078-5-W_Armin@gmx.deReviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

drivers/platform/x86/amd/pmf/tee-if.c

@@ -249,11 +249,17 @@ static int amd_pmf_start_policy_engine(struct amd_pmf_dev *dev)
 	struct cookie_header *header;
 	int res;
 
+	if (dev->policy_sz < POLICY_COOKIE_OFFSET + sizeof(*header))
+		return -EINVAL;
+
 	header = (struct cookie_header *)(dev->policy_buf + POLICY_COOKIE_OFFSET);
 
 	if (header->sign != POLICY_SIGN_COOKIE || !header->length)
 		return -EINVAL;
 
+	if (dev->policy_sz < header->length + 512)
+		return -EINVAL;
+
 	/* Update the actual length */
 	dev->policy_sz = header->length + 512;
 	res = amd_pmf_invoke_cmd_init(dev);