[PATCH v1 6/6] arm64: Enable RW, RX and RO mappings for the relocated binary

[Ilias Apalodimas]

Now that we have everything in place switch the page permissions for
.rodata, .text and .data just after we relocate everything in top of the
RAM.

Unfortunately we can't enable this by default, since we have examples of
U-Boot crashing due to invalid access. This usually happens because code
defines const variables that it later writes. So hide it behind a Kconfig
option until we sort it out.

It's worth noting that EFI runtime services are not covered by this
patch on purpose. Since the OS can call SetVirtualAddressMap which can
relocate runtime services, we need to set them to RX initially but remap
them as RWX right before ExitBootServices.

Link: https://lore.kernel.org/u-boot/20250129-rockchip-pinctrl-const-v1-0-450ccdadfa7e@cherry.de/
Link: https://lore.kernel.org/u-boot/20250130133646.2177194-1-andre.przywara@arm.com/
Signed-off-by: Ilias Apalodimas <ilias.apalodimas at linaro.org>
---
 common/Kconfig   | 13 +++++++++++++
 common/board_r.c | 20 ++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/common/Kconfig b/common/Kconfig
index 7685914fa6fd..dbae7e062b0a 100644
--- a/common/Kconfig
+++ b/common/Kconfig
@@ -914,6 +914,19 @@ config STACKPROTECTOR
 	  Enable stack smash detection through compiler's stack-protector
 	  canary logic
 
+config MMU_PGPROT
+	bool "Enable RO, RW and RX mappings"
+	help
+	  U-Boot maps all pages as RWX. If selected pages will
+	  be marked as RO(.rodata), RX(.text), RW(.data) right after
+	  we relocate. Since code sections needs to be page aligned
+	  the final binary size will increase.
+	  The mapping can be dumped using the 'meminfo' command.
+	  We should make this default 'y' in the future, but currently
+	  we have code defining const variables that are later written.
+	  Enabling this will crash U-Boot if that code path runs, so keep
+	  it off by default until we fix invalid accesses.
+
 config SPL_STACKPROTECTOR
 	bool "Stack Protector buffer overflow detection for SPL"
 	depends on STACKPROTECTOR && SPL
diff --git a/common/board_r.c b/common/board_r.c
index 179259b00de8..c1e9aa46e3fa 100644
--- a/common/board_r.c
+++ b/common/board_r.c
@@ -170,7 +170,27 @@ static int initr_reloc_global_data(void)
 	efi_save_gd();
 
 	efi_runtime_relocate(gd->relocaddr, NULL);
+
 #endif
+	/*
+	 * We are done with all relocations change the permissions of the binary
+	 * NOTE: __start_rodata etc are defined in arm64 linker scripts and
+	 * sections.h. If you want to add support for your platform you need to
+	 * add the symbols on your linker script, otherwise they will point to
+	 * random addresses.
+	 *
+	 */
+	if (IS_ENABLED(CONFIG_MMU_PGPROT)) {
+		pgprot_set_attrs((phys_addr_t)(uintptr_t)(__start_rodata),
+				 (phys_addr_t)(uintptr_t)(__end_rodata - __start_rodata),
+				 MMU_ATTR_RO);
+		pgprot_set_attrs((phys_addr_t)(uintptr_t)(__start_data),
+				 (phys_addr_t)(uintptr_t)(__end_data - __start_data),
+				 MMU_ATTR_RW);
+		pgprot_set_attrs((phys_addr_t)(uintptr_t)(__text_start),
+				 (phys_addr_t)(uintptr_t)(__text_end - __text_start),
+				 MMU_ATTR_RX);
+	}
 
 	return 0;
 }
-- 
2.47.2