[PATCH v2 2/2] arm: separate .data and .text sections of EFI binaries

[Heinrich Schuchardt]

EFI binaries should not contain sections that are both writable and
executable. Separate the RX .text section from the RW .data section.

We currently don't created relocation sections (.rel.*) for our EFI
binaries. Anyway these would have to be converted to PE/COFF relocations.
Enumerate them under DISCARD and add a comment.

Correct the characteristics of the sections.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt at canonical.com>
---
v2:
	Consider that 32-bit arm uses .rel and not .rela relocations
	and discard them as they are cannot be used in EFI binaries.
	Correct the characteristics of the .reloc section.
---
 arch/arm/lib/crt0_arm_efi.S  | 40 ++++++++++++++++++++++++++++--------
 arch/arm/lib/elf_arm_efi.lds | 28 ++++++++++++++++++-------
 2 files changed, 52 insertions(+), 16 deletions(-)

diff --git a/arch/arm/lib/crt0_arm_efi.S b/arch/arm/lib/crt0_arm_efi.S
index 7a4e5dff75..7219c0f2fe 100644
--- a/arch/arm/lib/crt0_arm_efi.S
+++ b/arch/arm/lib/crt0_arm_efi.S
@@ -23,7 +23,7 @@ pe_header:
 	.long	IMAGE_NT_SIGNATURE		/* 'PE' */
 coff_header:
 	.short	IMAGE_FILE_MACHINE_THUMB	/* Mixed ARM/Thumb */
-	.short	2				/* nr_sections */
+	.short	3				/* nr_sections */
 	.long	0				/* TimeDateStamp */
 	.long	0				/* PointerToSymbolTable */
 	.long	0				/* NumberOfSymbols */
@@ -98,22 +98,44 @@ section_table:
 	.long	0			/* PointerToLineNumbers */
 	.short	0			/* NumberOfRelocations */
 	.short	0			/* NumberOfLineNumbers */
-	.long	0x42100040		/* Characteristics (section flags) */
+	/* Characteristics (section flags) */
+	.long	(IMAGE_SCN_MEM_READ | \
+		 IMAGE_SCN_MEM_DISCARDABLE | \
+		 IMAGE_SCN_CNT_INITIALIZED_DATA)
 
 	.ascii	".text"
 	.byte	0
 	.byte	0
 	.byte	0			/* end of 0 padding of section name */
-	.long	_edata - _start		/* VirtualSize */
+	.long	_text_size		/* VirtualSize */
 	.long	_start - image_base	/* VirtualAddress */
-	.long	_edata - _start		/* SizeOfRawData */
+	.long	_text_size		/* SizeOfRawData */
 	.long	_start - image_base	/* PointerToRawData */
+	.long	0			/* PointerToRelocations */
+	.long	0			/* PointerToLineNumbers */
+	.short	0			/* NumberOfRelocations */
+	.short	0			/* NumberOfLineNumbers */
+	/* Characteristics (section flags) */
+	.long	(IMAGE_SCN_MEM_READ | \
+		 IMAGE_SCN_MEM_EXECUTE | \
+		 IMAGE_SCN_CNT_CODE)
 
-	.long	0		/* PointerToRelocations (0 for executables) */
-	.long	0		/* PointerToLineNumbers (0 for executables) */
-	.short	0		/* NumberOfRelocations  (0 for executables) */
-	.short	0		/* NumberOfLineNumbers  (0 for executables) */
-	.long	0xe0500020	/* Characteristics (section flags) */
+	.ascii	".data"
+	.byte	0
+	.byte	0
+	.byte	0			/* end of 0 padding of section name */
+	.long	_data_size		/* VirtualSize */
+	.long	_data - image_base	/* VirtualAddress */
+	.long	_data_size		/* SizeOfRawData */
+	.long	_data - image_base	/* PointerToRawData */
+	.long	0			/* PointerToRelocations */
+	.long	0			/* PointerToLineNumbers */
+	.short	0			/* NumberOfRelocations */
+	.short	0			/* NumberOfLineNumbers */
+	/* Characteristics (section flags) */
+	.long	(IMAGE_SCN_MEM_WRITE | \
+		 IMAGE_SCN_MEM_READ | \
+		 IMAGE_SCN_CNT_INITIALIZED_DATA)
 
 	.align		12
 _start:
diff --git a/arch/arm/lib/elf_arm_efi.lds b/arch/arm/lib/elf_arm_efi.lds
index 767ebda635..41440594aa 100644
--- a/arch/arm/lib/elf_arm_efi.lds
+++ b/arch/arm/lib/elf_arm_efi.lds
@@ -7,6 +7,12 @@
 
 OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 OUTPUT_ARCH(arm)
+
+PHDRS
+{
+	data PT_LOAD FLAGS(3); /* PF_W | PF_X */
+}
+
 ENTRY(_start)
 SECTIONS
 {
@@ -18,11 +24,13 @@ SECTIONS
 		*(.gnu.linkonce.t.*)
 		*(.srodata)
 		*(.rodata*)
+		. = ALIGN(16);
+		*(.dynamic);
 		. = ALIGN(512);
 	}
 	_etext = .;
 	_text_size = . - _text;
-	.dynamic  : { *(.dynamic) }
+	. = ALIGN(4096);
 	.data : {
 		_data = .;
 		*(.sdata)
@@ -47,14 +55,20 @@ SECTIONS
 		. = ALIGN(512);
 		_bss_end = .;
 		_edata = .;
-	}
-	.rel.dyn : { *(.rel.dyn) }
-	.rel.plt : { *(.rel.plt) }
-	.rel.got : { *(.rel.got) }
-	.rel.data : { *(.rel.data) *(.rel.data*) }
-	_data_size = . - _etext;
+	} :data
+	_data_size = . - _data;
 
 	/DISCARD/ : {
+		/*
+		 * We don't support relocations. These would have to be
+		 * translated from ELF to PE format and added to the .reloc
+		 * section.
+		 */
+		*(.rel.dyn)
+		*(.rel.plt)
+		*(.rel.got)
+		*(.rel.data)
+		*(.rel.data*)
 		*(.rel.reloc)
 		*(.eh_frame)
 		*(.note.GNU-stack)
-- 
2.43.0