arm64: efi: split Image code and data into separate PE/COFF sections

To prevent unintended modifications to the kernel text (malicious or
otherwise) while running the EFI stub, describe the kernel image as
two separate sections: a .text section with read-execute permissions,
covering .text, .rodata and .init.text, and a .data section with
read-write permissions, covering .init.data, .data and .bss.

This relies on the firmware to actually take the section permission
flags into account, but this is something that is currently being
implemented in EDK2, which means we will likely start seeing it in
the wild between one and two years from now.

Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

2 files changed, 20 insertions, 5 deletions

diff --git a/arch/arm64/kernel/efi-header.S b/arch/arm64/kernel/efi-header.S
index 7637226ea9ca..613fc3000677 100644
--- a/arch/arm64/kernel/efi-header.S
+++ b/arch/arm64/kernel/efi-header.S
@@ -27,8 +27,8 @@ optional_header:
         .short  PE_OPT_MAGIC_PE32PLUS                   // PE32+ format
         .byte   0x02                                    // MajorLinkerVersion
         .byte   0x14                                    // MinorLinkerVersion
-        .long   _end - efi_header_end                   // SizeOfCode
-        .long   0                                       // SizeOfInitializedData
+        .long   __initdata_begin - efi_header_end       // SizeOfCode
+        .long   __pecoff_data_size                      // SizeOfInitializedData
         .long   0                                       // SizeOfUninitializedData
         .long   __efistub_entry - _head                 // AddressOfEntryPoint
         .long   efi_header_end - _head                  // BaseOfCode
@@ -74,9 +74,9 @@ extra_header_fields:
         // Section table
 section_table:
         .ascii  ".text\0\0\0"
-        .long   _end - efi_header_end                   // VirtualSize
+        .long   __initdata_begin - efi_header_end       // VirtualSize
         .long   efi_header_end - _head                  // VirtualAddress
-        .long   _edata - efi_header_end                 // SizeOfRawData
+        .long   __initdata_begin - efi_header_end       // SizeOfRawData
         .long   efi_header_end - _head                  // PointerToRawData
 
         .long   0                                       // PointerToRelocations
@@ -84,7 +84,20 @@ section_table:
         .short  0                                       // NumberOfRelocations
         .short  0                                       // NumberOfLineNumbers
         .long   IMAGE_SCN_CNT_CODE | \
-                IMAGE_SCN_MEM_EXECUTE | \
+                IMAGE_SCN_MEM_READ | \
+                IMAGE_SCN_MEM_EXECUTE                   // Characteristics
+
+        .ascii  ".data\0\0\0"
+        .long   __pecoff_data_size                      // VirtualSize
+        .long   __initdata_begin - _head                // VirtualAddress
+        .long   __pecoff_data_rawsize                   // SizeOfRawData
+        .long   __initdata_begin - _head                // PointerToRawData
+
+        .long   0                                       // PointerToRelocations
+        .long   0                                       // PointerToLineNumbers
+        .short  0                                       // NumberOfRelocations
+        .short  0                                       // NumberOfLineNumbers
+        .long   IMAGE_SCN_CNT_INITIALIZED_DATA | \
                 IMAGE_SCN_MEM_READ | \
                 IMAGE_SCN_MEM_WRITE                     // Characteristics
 
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index 2c93d259046c..987a00ee446c 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -213,6 +213,7 @@ SECTIONS
         }
 
         PECOFF_EDATA_PADDING
+        __pecoff_data_rawsize = ABSOLUTE(. - __initdata_begin);
         _edata = .;
 
         BSS_SECTION(0, 0, 0)
@@ -228,6 +229,7 @@ SECTIONS
         . += RESERVED_TTBR0_SIZE;
 #endif
 
+        __pecoff_data_size = ABSOLUTE(. - __initdata_begin);
         _end = .;
 
         STABS_DEBUG