[PATCH] usb: gadget: sdp: Option to enable SDP read register command

[Loic Poulain]

The SDP read register command can be used to read any memory
mapped address of the device (ddr, registers...). It can then
be exploited by an attacker to access sensitive data/values,
especially when running SDP from SPL, as SPL runs with highest
privileges in ARM secure mode.

Without read, SDP still useful to bootstrap and jump on (signed)
blob such as u-boot with write and jump commands, but reading
is optional in that case (debug purpose).

NXP SoCs usually have a dedicated SDP_READ_DISABLE fuse to disable
SDP read command in their ROM SDP implementation, so it seems quite
reasonable to make it optional from u-boot/spl as well.

Signed-off-by: Loic Poulain <loic.poulain at linaro.org>
---
 drivers/usb/gadget/Kconfig | 14 ++++++++++++++
 drivers/usb/gadget/f_sdp.c |  2 ++
 2 files changed, 16 insertions(+)

diff --git a/drivers/usb/gadget/Kconfig b/drivers/usb/gadget/Kconfig
index 1cfe602284..50cf7c0dae 100644
--- a/drivers/usb/gadget/Kconfig
+++ b/drivers/usb/gadget/Kconfig
@@ -195,6 +195,13 @@ config USB_FUNCTION_SDP
 	  allows to download images into memory and execute (jump to) them
 	  using the same protocol as implemented by the i.MX family's boot ROM.
 
+config SDP_READ
+	bool "Enable SDP READ command"
+	depends on USB_FUNCTION_SDP
+	default n
+	help
+	  Enable SDP secure sensitive SDP read register command.
+
 config USB_FUNCTION_THOR
 	bool "Enable USB THOR gadget"
 	help
@@ -344,6 +351,13 @@ config SPL_USB_SDP_SUPPORT
 	  allows to download images into memory and execute (jump to) them
 	  using the same protocol as implemented by the i.MX family's boot ROM.
 
+config SPL_SDP_READ
+	bool "Enable SDP READ command in SPL"
+	depends on SPL_USB_SDP_SUPPORT
+	default n
+	help
+	  Enable SDP secure sensitive SDP read register command.
+
 config SPL_SDP_USB_DEV
 	int "SDP USB controller index in SPL"
 	default 0
diff --git a/drivers/usb/gadget/f_sdp.c b/drivers/usb/gadget/f_sdp.c
index 4da5a160a0..48a68a50d9 100644
--- a/drivers/usb/gadget/f_sdp.c
+++ b/drivers/usb/gadget/f_sdp.c
@@ -310,6 +310,7 @@ static void sdp_rx_command_complete(struct usb_ep *ep, struct usb_request *req)
 	      be32_to_cpu(cmd->addr), be32_to_cpu(cmd->cnt));
 
 	switch (be16_to_cpu(cmd->cmd)) {
+#if CONFIG_IS_ENABLED(SDP_READ)
 	case SDP_READ_REGISTER:
 		sdp->always_send_status = false;
 		sdp->error_status = 0x0;
@@ -321,6 +322,7 @@ static void sdp_rx_command_complete(struct usb_ep *ep, struct usb_request *req)
 		printf("Reading %d registers at 0x%08x... ",
 		       sdp->dnl_bytes_remaining, sdp->dnl_address);
 		break;
+#endif
 	case SDP_WRITE_FILE:
 		sdp->always_send_status = true;
 		sdp->error_status = SDP_WRITE_FILE_COMPLETE;
-- 
2.34.1