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Commit 1e48ef7f authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Catalin Marinas
Browse files

arm64: add support for building vmlinux as a relocatable PIE binary 



This implements CONFIG_RELOCATABLE, which links the final vmlinux
image with a dynamic relocation section, allowing the early boot code
to perform a relocation to a different virtual address at runtime.

This is a prerequisite for KASLR (CONFIG_RANDOMIZE_BASE).

Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarCatalin Marinas <catalin.marinas@arm.com>
parent 6c94f27a

arch/arm64/Kconfig

+11 −0
Original line number Diff line number Diff line
@@ -787,6 +787,17 @@ config ARM64_MODULE_PLTS 
	select ARM64_MODULE_CMODEL_LARGE

	select HAVE_MOD_ARCH_SPECIFIC



config RELOCATABLE

	bool

	help

	  This builds the kernel as a Position Independent Executable (PIE),

	  which retains all relocation metadata required to relocate the

	  kernel binary at runtime to a different virtual address than the

	  address it was linked at.

	  Since AArch64 uses the RELA relocation format, this requires a

	  relocation pass at runtime even if the kernel is loaded at the

	  same address it was linked at.



endmenu



menu "Boot options"

arch/arm64/Makefile

+4 −0
Original line number Diff line number Diff line
@@ -15,6 +15,10 @@ CPPFLAGS_vmlinux.lds = -DTEXT_OFFSET=$(TEXT_OFFSET) 
OBJCOPYFLAGS	:=-O binary -R .note -R .note.gnu.build-id -R .comment -S

GZFLAGS		:=-9



ifneq ($(CONFIG_RELOCATABLE),)

LDFLAGS_vmlinux		+= -pie

endif



KBUILD_DEFCONFIG := defconfig



# Check for binutils support for specific extensions

arch/arm64/include/asm/elf.h

+2 −0
Original line number Diff line number Diff line
@@ -77,6 +77,8 @@ 
#define R_AARCH64_MOVW_PREL_G2_NC	292

#define R_AARCH64_MOVW_PREL_G3		293



#define R_AARCH64_RELATIVE		1027



/*

 * These are used to set parameters in the core dumps.

 */

arch/arm64/kernel/head.S

+32 −0
Original line number Diff line number Diff line
@@ -29,6 +29,7 @@ 
#include <asm/asm-offsets.h>

#include <asm/cache.h>

#include <asm/cputype.h>

#include <asm/elf.h>

#include <asm/kernel-pgtable.h>

#include <asm/memory.h>

#include <asm/pgtable-hwdef.h>
@@ -432,6 +433,37 @@ __mmap_switched: 
	bl	__pi_memset

	dsb	ishst				// Make zero page visible to PTW



#ifdef CONFIG_RELOCATABLE



	/*

	 * Iterate over each entry in the relocation table, and apply the

	 * relocations in place.

	 */

	adr_l	x8, __dynsym_start		// start of symbol table

	adr_l	x9, __reloc_start		// start of reloc table

	adr_l	x10, __reloc_end		// end of reloc table



0:	cmp	x9, x10

	b.hs	2f

	ldp	x11, x12, [x9], #24

	ldr	x13, [x9, #-8]

	cmp	w12, #R_AARCH64_RELATIVE

	b.ne	1f

	str	x13, [x11]

	b	0b



1:	cmp	w12, #R_AARCH64_ABS64

	b.ne	0b

	add	x12, x12, x12, lsl #1		// symtab offset: 24x top word

	add	x12, x8, x12, lsr #(32 - 3)	// ... shifted into bottom word

	ldr	x15, [x12, #8]			// Elf64_Sym::st_value

	add	x15, x13, x15

	str	x15, [x11]

	b	0b



2:

#endif



	adr_l	sp, initial_sp, x4

	mov	x4, sp

	and	x4, x4, #~(THREAD_SIZE - 1)

arch/arm64/kernel/vmlinux.lds.S

+16 −0
Original line number Diff line number Diff line
@@ -87,6 +87,7 @@ SECTIONS 
		EXIT_CALL

		*(.discard)

		*(.discard.*)

		*(.interp .dynamic)

	}



	. = KIMAGE_VADDR + TEXT_OFFSET;
@@ -149,6 +150,21 @@ SECTIONS 
	.altinstr_replacement : {

		*(.altinstr_replacement)

	}

	.rela : ALIGN(8) {

		__reloc_start = .;

		*(.rela .rela*)

		__reloc_end = .;

	}

	.dynsym : ALIGN(8) {

		__dynsym_start = .;

		*(.dynsym)

	}

	.dynstr : {

		*(.dynstr)

	}

	.hash : {

		*(.hash)

	}



	. = ALIGN(PAGE_SIZE);

	__init_end = .;