remoteproc: qcom_q6v5_mss: Use a carveout to authenticate modem headers

Any access to the dynamically allocated metadata region by the application
processor after assigning it to the remote Q6 will result in a XPU
violation. Fix this by replacing the dynamically allocated memory region
with a no-map carveout and unmap the modem metadata memory region before
passing control to the remote Q6.
Reported-and-tested-by: Amit Pundir <amit.pundir@linaro.org>
Fixes: 6c5a9dc2 ("remoteproc: qcom: Make secure world call for mem ownership switch")
Signed-off-by: Sibi Sankar <quic_sibis@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230117085840.32356-7-quic_sibis@quicinc.com

drivers/remoteproc/qcom_q6v5_mss.c

@@ -17,6 +17,7 @@
 #include <linux/module.h>
 #include <linux/of_address.h>
 #include <linux/of_device.h>
+#include <linux/of_reserved_mem.h>
 #include <linux/platform_device.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_runtime.h>
@@ -215,6 +216,9 @@ struct q6v5 {
 	size_t mba_size;
 	size_t dp_size;
 
+	phys_addr_t mdata_phys;
+	size_t mdata_size;
+
 	phys_addr_t mpss_phys;
 	phys_addr_t mpss_reloc;
 	size_t mpss_size;
@@ -973,15 +977,35 @@ static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
 	if (IS_ERR(metadata))
 		return PTR_ERR(metadata);
 
-	ptr = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
-	if (!ptr) {
-		kfree(metadata);
-		dev_err(qproc->dev, "failed to allocate mdt buffer\n");
-		return -ENOMEM;
+	if (qproc->mdata_phys) {
+		if (size > qproc->mdata_size) {
+			ret = -EINVAL;
+			dev_err(qproc->dev, "metadata size outside memory range\n");
+			goto free_metadata;
+		}
+
+		phys = qproc->mdata_phys;
+		ptr = memremap(qproc->mdata_phys, size, MEMREMAP_WC);
+		if (!ptr) {
+			ret = -EBUSY;
+			dev_err(qproc->dev, "unable to map memory region: %pa+%zx\n",
+				&qproc->mdata_phys, size);
+			goto free_metadata;
+		}
+	} else {
+		ptr = dma_alloc_attrs(qproc->dev, size, &phys, GFP_KERNEL, dma_attrs);
+		if (!ptr) {
+			ret = -ENOMEM;
+			dev_err(qproc->dev, "failed to allocate mdt buffer\n");
+			goto free_metadata;
+		}
 	}
 
 	memcpy(ptr, metadata, size);
 
+	if (qproc->mdata_phys)
+		memunmap(ptr);
+
 	/* Hypervisor mapping to access metadata by modem */
 	mdata_perm = BIT(QCOM_SCM_VMID_HLOS);
 	ret = q6v5_xfer_mem_ownership(qproc, &mdata_perm, false, true,
@@ -1010,7 +1034,9 @@ static int q6v5_mpss_init_image(struct q6v5 *qproc, const struct firmware *fw,
 			 "mdt buffer not reclaimed system may become unstable\n");
 
 free_dma_attrs:
-	dma_free_attrs(qproc->dev, size, ptr, phys, dma_attrs);
+	if (!qproc->mdata_phys)
+		dma_free_attrs(qproc->dev, size, ptr, phys, dma_attrs);
+free_metadata:
 	kfree(metadata);
 
 	return ret < 0 ? ret : 0;
@@ -1847,6 +1873,7 @@ static int q6v5_init_reset(struct q6v5 *qproc)
 static int q6v5_alloc_memory_region(struct q6v5 *qproc)
 {
 	struct device_node *child;
+	struct reserved_mem *rmem;
 	struct device_node *node;
 	struct resource r;
 	int ret;
@@ -1893,6 +1920,26 @@ static int q6v5_alloc_memory_region(struct q6v5 *qproc)
 	qproc->mpss_phys = qproc->mpss_reloc = r.start;
 	qproc->mpss_size = resource_size(&r);
 
+	if (!child) {
+		node = of_parse_phandle(qproc->dev->of_node, "memory-region", 2);
+	} else {
+		child = of_get_child_by_name(qproc->dev->of_node, "metadata");
+		node = of_parse_phandle(child, "memory-region", 0);
+		of_node_put(child);
+	}
+
+	if (!node)
+		return 0;
+
+	rmem = of_reserved_mem_lookup(node);
+	if (!rmem) {
+		dev_err(qproc->dev, "unable to resolve metadata region\n");
+		return -EINVAL;
+	}
+
+	qproc->mdata_phys = rmem->base;
+	qproc->mdata_size = rmem->size;
+
 	return 0;
 }