[PATCH 1/2] memory: brcmstb_dpfe: Fix out-of-bounds access due to DCPU offset

[Danesh Petigara <danesh.petigara@broadcom.com>]

From: Justin Chen <justin.chen@broadcom.com>

On API v1/v2 boards, the DCPU coprocessor can steer kernel readl_relaxed()
and writel_relaxed() to any address within 256 MB of the ioremapped DPFE
dmem or regs base. The DCPU firmware provides a 28-bit offset which the
driver adds to the ioremap base without any bounds checking in
get_msg_ptr().

This allows a compromised DCPU firmware to trick the host kernel into
reading or writing arbitrary memory-mapped I/O registers in vmalloc
space. When combined with a root-writable sysfs file like dpfe_refresh,
it provides an arbitrary MMIO write primitive. Similarly, world-readable
sysfs files can be used to leak other devices' register contents.

Fix this by recording the resource_size() of the dmem and regs ioremaps
at probe time, and rejecting any offset that, along with the largest
field accessed (DRAM_VENDOR_ERROR + sizeof(u32)), exceeds the recorded
mapping size.

Fixes: fee5f1ef6cf7 ("memory: brcmstb: dpfe: support new way of passing data from the DCPU")
Cc: stable@vger.kernel.org
Signed-off-by: Justin Chen <justin.chen@broadcom.com>
Assisted-by: Gemini:gemini-3.1-pro-preview cursor
Signed-off-by: Danesh Petigara <danesh.petigara@broadcom.com>
---
 drivers/memory/brcmstb_dpfe.c | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/drivers/memory/brcmstb_dpfe.c b/drivers/memory/brcmstb_dpfe.c
index 08d9e05b1b33..66343205f585 100644
--- a/drivers/memory/brcmstb_dpfe.c
+++ b/drivers/memory/brcmstb_dpfe.c
@@ -182,6 +182,8 @@ struct brcmstb_dpfe_priv {
 	void __iomem *regs;
 	void __iomem *dmem;
 	void __iomem *imem;
+	resource_size_t regs_size;
+	resource_size_t dmem_size;
 	struct device *dev;
 	const struct dpfe_api *dpfe_api;
 	struct mutex lock;
@@ -401,9 +403,14 @@ static void __iomem *get_msg_ptr(struct brcmstb_dpfe_priv *priv, u32 response,
 	 */
 	switch (msg_type) {
 	case 1:
+		if (DCPU_MSG_RAM_START + offset + DRAM_VENDOR_ERROR +
+		    sizeof(u32) > priv->regs_size)
+			goto bad_offset;
 		ptr = priv->regs + DCPU_MSG_RAM_START + offset;
 		break;
 	case 0:
+		if (offset + DRAM_VENDOR_ERROR + sizeof(u32) > priv->dmem_size)
+			goto bad_offset;
 		ptr = priv->dmem + offset;
 		break;
 	default:
@@ -415,6 +422,12 @@ static void __iomem *get_msg_ptr(struct brcmstb_dpfe_priv *priv, u32 response,
 	}
 
 	return ptr;
+
+bad_offset:
+	dev_err(priv->dev, "DCPU returned out-of-range offset %#x\n", offset);
+	if (buf && size)
+		*size = sprintf(buf, "ERROR: DCPU offset out of range\n");
+	return NULL;
 }
 
 static void __finalize_command(struct brcmstb_dpfe_priv *priv)
@@ -858,6 +871,7 @@ static int brcmstb_dpfe_probe(struct platform_device *pdev)
 {
 	struct device *dev = &pdev->dev;
 	struct brcmstb_dpfe_priv *priv;
+	struct resource *res;
 	int ret;
 
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
@@ -869,17 +883,21 @@ static int brcmstb_dpfe_probe(struct platform_device *pdev)
 	mutex_init(&priv->lock);
 	platform_set_drvdata(pdev, priv);
 
-	priv->regs = devm_platform_ioremap_resource_byname(pdev, "dpfe-cpu");
+	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dpfe-cpu");
+	priv->regs = devm_ioremap_resource(dev, res);
 	if (IS_ERR(priv->regs)) {
 		dev_err(dev, "couldn't map DCPU registers\n");
 		return -ENODEV;
 	}
+	priv->regs_size = resource_size(res);
 
-	priv->dmem = devm_platform_ioremap_resource_byname(pdev, "dpfe-dmem");
+	res = platform_get_resource_byname(pdev, IORESOURCE_MEM, "dpfe-dmem");
+	priv->dmem = devm_ioremap_resource(dev, res);
 	if (IS_ERR(priv->dmem)) {
 		dev_err(dev, "Couldn't map DCPU data memory\n");
 		return -ENOENT;
 	}
+	priv->dmem_size = resource_size(res);
 
 	priv->imem = devm_platform_ioremap_resource_byname(pdev, "dpfe-imem");
 	if (IS_ERR(priv->imem)) {
-- 
2.54.0