[PATCH 1/1] efi_loader: set IMAGE_DLLCHARACTERISTICS_NX_COMPAT

[Heinrich Schuchardt]

The IMAGE_DLLCHARACTERISTICS_NX_COMPAT flag marks an EFI binary where
the following conditions are met [1]:

* Executable and writable sections are separated.
* The application does not run self-modifying code.
* The application uses the EFI_MEMORY_ATTRIBUTE_PROTOCOL when loading
  executable code.
* The application does not assume that all memory ranges are usable.
* The stack is not expected to be executable.

The only EFI binaries U-Boot provides that do not fulfill these
requirements are the EFI app and the EFI payload.

Once we have implemented separation of writable and executable memory in
U-Boot we can use the IMAGE_DLLCHARACTERISTICS_NX_COMPAT flag to decide
if we will load an EFI binary.

[1] New UEFI CA memory mitigation requirements for signing
    https://techcommunity.microsoft.com/t5/hardware-dev-center/new-uefi-ca-memory-mitigation-requirements-for-signing/ba-p/3608714

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
The separation of executable and writable sections for armv7 EFI binaries
is provided by

[PATCH 1/1] arm: separate .data and .text sections of EFI binaries
https://lore.kernel.org/u-boot/20240214190625.13764-1-heinrich.schuchardt@canonical.com/T/#u
---
 arch/arm/lib/crt0_aarch64_efi.S | 4 ++++
 arch/arm/lib/crt0_arm_efi.S     | 4 ++++
 arch/riscv/lib/crt0_riscv_efi.S | 4 ++++
 include/asm-generic/pe.h        | 3 +++
 4 files changed, 15 insertions(+)

diff --git a/arch/arm/lib/crt0_aarch64_efi.S b/arch/arm/lib/crt0_aarch64_efi.S
index 3c2cef6ec7..fe6eca576e 100644
--- a/arch/arm/lib/crt0_aarch64_efi.S
+++ b/arch/arm/lib/crt0_aarch64_efi.S
@@ -66,7 +66,11 @@ extra_header_fields:
 	.long	_start - ImageBase		/* SizeOfHeaders */
 	.long	0				/* CheckSum */
 	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION /* Subsystem */
+#if CONFIG_VENDOR_EFI
 	.short	0				/* DllCharacteristics */
+#else
+	.short	IMAGE_DLLCHARACTERISTICS_NX_COMPAT
+#endif
 	.quad	0				/* SizeOfStackReserve */
 	.quad	0				/* SizeOfStackCommit */
 	.quad	0				/* SizeOfHeapReserve */
diff --git a/arch/arm/lib/crt0_arm_efi.S b/arch/arm/lib/crt0_arm_efi.S
index ba9fada500..afeff3f3fb 100644
--- a/arch/arm/lib/crt0_arm_efi.S
+++ b/arch/arm/lib/crt0_arm_efi.S
@@ -65,7 +65,11 @@ extra_header_fields:
 	.long	_start - image_base		/* SizeOfHeaders */
 	.long	0				/* CheckSum */
 	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION	/* Subsystem */
+#if CONFIG_VENDOR_EFI
 	.short	0				/* DllCharacteristics */
+#else
+	.short	IMAGE_DLLCHARACTERISTICS_NX_COMPAT
+#endif
 	.long	0				/* SizeOfStackReserve */
 	.long	0				/* SizeOfStackCommit */
 	.long	0				/* SizeOfHeapReserve */
diff --git a/arch/riscv/lib/crt0_riscv_efi.S b/arch/riscv/lib/crt0_riscv_efi.S
index 46b0855237..c7a4559eac 100644
--- a/arch/riscv/lib/crt0_riscv_efi.S
+++ b/arch/riscv/lib/crt0_riscv_efi.S
@@ -96,7 +96,11 @@ extra_header_fields:
 	.long	_start - ImageBase		/* SizeOfHeaders */
 	.long	0				/* CheckSum */
 	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION /* Subsystem */
+#if CONFIG_VENDOR_EFI
 	.short	0				/* DllCharacteristics */
+#else
+	.short	IMAGE_DLLCHARACTERISTICS_NX_COMPAT
+#endif
 #if __riscv_xlen == 32
 	.long	0				/* SizeOfStackReserve */
 	.long	0				/* SizeOfStackCommit */
diff --git a/include/asm-generic/pe.h b/include/asm-generic/pe.h
index b9d674b6da..cd5b6ad62b 100644
--- a/include/asm-generic/pe.h
+++ b/include/asm-generic/pe.h
@@ -51,6 +51,9 @@
 #define IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER	12
 #define IMAGE_SUBSYSTEM_EFI_ROM			13
 
+/* DLL characteristics */
+#define IMAGE_DLLCHARACTERISTICS_NX_COMPAT	0x100
+
 /* Section flags */
 #define IMAGE_SCN_CNT_CODE			0x00000020
 #define IMAGE_SCN_CNT_INITIALIZED_DATA		0x00000040
-- 
2.43.0