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

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
......@@ -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"
......
......@@ -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
......
......@@ -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.
*/
......
......@@ -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)
......
......@@ -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 = .;
......
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