Messages in this thread Patch in this message | | | From | Youling Tang <> | Subject | [PATCH v5 4/5] LoongArch: Add support for kernel relocation | Date | Fri, 17 Feb 2023 15:26:28 +0800 |
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This config allows to compile kernel as PIE and to relocate it at any virtual address at runtime: this paves the way to KASLR. Runtime relocation is possible since relocation metadata are embedded into the kernel.
Signed-off-by: Youling Tang <tangyouling@loongson.cn> Signed-off-by: Xi Ruoyao <xry111@xry111.site> # Use arch_initcall Signed-off-by: Jinyang He <hejinyang@loongson.cn> # Provide la_abs idea --- arch/loongarch/Kconfig | 8 ++ arch/loongarch/Makefile | 5 ++ arch/loongarch/include/asm/asmmacro.h | 13 ++++ arch/loongarch/include/asm/setup.h | 14 ++++ arch/loongarch/kernel/Makefile | 2 + arch/loongarch/kernel/head.S | 5 ++ arch/loongarch/kernel/relocate.c | 104 ++++++++++++++++++++++++++ arch/loongarch/kernel/vmlinux.lds.S | 20 ++++- 8 files changed, 169 insertions(+), 2 deletions(-) create mode 100644 arch/loongarch/kernel/relocate.c
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig index 54bd3dbde1f2..406a28758a52 100644 --- a/arch/loongarch/Kconfig +++ b/arch/loongarch/Kconfig @@ -522,6 +522,14 @@ config PHYSICAL_START specified in the "crashkernel=YM@XM" command line boot parameter passed to the panic-ed kernel). +config RELOCATABLE + bool "Relocatable kernel" + 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. + config SECCOMP bool "Enable seccomp to safely compute untrusted bytecode" depends on PROC_FS diff --git a/arch/loongarch/Makefile b/arch/loongarch/Makefile index ccfb52700237..2aba6ff30436 100644 --- a/arch/loongarch/Makefile +++ b/arch/loongarch/Makefile @@ -71,6 +71,11 @@ KBUILD_AFLAGS_MODULE += -Wa,-mla-global-with-abs KBUILD_CFLAGS_MODULE += -fplt -Wa,-mla-global-with-abs,-mla-local-with-abs endif +ifeq ($(CONFIG_RELOCATABLE),y) +LDFLAGS_vmlinux += -static -pie --no-dynamic-linker -z notext +KBUILD_CFLAGS_KERNEL += -fPIE +endif + cflags-y += -ffreestanding cflags-y += $(call cc-option, -mno-check-zero-division) diff --git a/arch/loongarch/include/asm/asmmacro.h b/arch/loongarch/include/asm/asmmacro.h index adc92464afa6..ba99908d7d10 100644 --- a/arch/loongarch/include/asm/asmmacro.h +++ b/arch/loongarch/include/asm/asmmacro.h @@ -668,7 +668,20 @@ .endm .macro la_abs reg, sym +#ifndef CONFIG_RELOCATABLE la.abs \reg, \sym +#else +766: + lu12i.w \reg, 0 + ori \reg, \reg, 0 + lu32i.d \reg, 0 + lu52i.d \reg, \reg, 0 + .pushsection ".la_abs", "aw", %progbits +768: + .dword 768b-766b + .dword \sym + .popsection +#endif .endm #endif /* _ASM_ASMMACRO_H */ diff --git a/arch/loongarch/include/asm/setup.h b/arch/loongarch/include/asm/setup.h index 72ead58039f3..efbd8d7b15df 100644 --- a/arch/loongarch/include/asm/setup.h +++ b/arch/loongarch/include/asm/setup.h @@ -21,4 +21,18 @@ extern void per_cpu_trap_init(int cpu); extern void set_handler(unsigned long offset, void *addr, unsigned long len); extern void set_merr_handler(unsigned long offset, void *addr, unsigned long len); +#ifdef CONFIG_RELOCATABLE +struct rela_la_abs { + long offset; + long symvalue; +}; + +extern long __rela_dyn_start; +extern long __rela_dyn_end; +extern void *__la_abs_begin; +extern void *__la_abs_end; + +extern void __init relocate_kernel(void); +#endif + #endif /* __SETUP_H */ diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile index 45c78aea63ce..3288854dbe36 100644 --- a/arch/loongarch/kernel/Makefile +++ b/arch/loongarch/kernel/Makefile @@ -31,6 +31,8 @@ endif obj-$(CONFIG_MODULES) += module.o module-sections.o obj-$(CONFIG_STACKTRACE) += stacktrace.o +obj-$(CONFIG_RELOCATABLE) += relocate.o + obj-$(CONFIG_PROC_FS) += proc.o obj-$(CONFIG_SMP) += smp.o diff --git a/arch/loongarch/kernel/head.S b/arch/loongarch/kernel/head.S index d2ac26b5b22b..499edc80d8ab 100644 --- a/arch/loongarch/kernel/head.S +++ b/arch/loongarch/kernel/head.S @@ -86,6 +86,11 @@ SYM_CODE_START(kernel_entry) # kernel entry point PTR_ADD sp, sp, tp set_saved_sp sp, t0, t1 +#ifdef CONFIG_RELOCATABLE + /* Apply the relocations */ + bl relocate_kernel +#endif + bl start_kernel ASM_BUG() diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c new file mode 100644 index 000000000000..6f31753be1da --- /dev/null +++ b/arch/loongarch/kernel/relocate.c @@ -0,0 +1,104 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Support for Kernel relocation at boot time + * + * Copyright (C) 2023 Loongson Technology Corporation Limited + */ + +#include <linux/elf.h> +#include <linux/kernel.h> +#include <linux/printk.h> +#include <linux/panic_notifier.h> +#include <asm/inst.h> +#include <asm/sections.h> +#include <asm/setup.h> + +#define RELOCATED(x) ((void *)((long)x + reloc_offset)) + +static unsigned long reloc_offset; + +static inline __init void relocate_relative(void) +{ + Elf64_Rela *rela, *rela_end; + rela = (Elf64_Rela *)&__rela_dyn_start; + rela_end = (Elf64_Rela *)&__rela_dyn_end; + + for ( ; rela < rela_end; rela++) { + Elf64_Addr addr = rela->r_offset; + Elf64_Addr relocated_addr = rela->r_addend; + + if (rela->r_info != R_LARCH_RELATIVE) + continue; + + if (relocated_addr >= VMLINUX_LOAD_ADDRESS) + relocated_addr = + (Elf64_Addr)RELOCATED(relocated_addr); + + *(Elf64_Addr *)RELOCATED(addr) = relocated_addr; + } +} + +static inline void __init relocate_la_abs(void) +{ + struct rela_la_abs *p; + + for (p = (void *)&__la_abs_begin; (void *)p < (void *)&__la_abs_end; p++) { + long v = p->symvalue + reloc_offset; + union loongarch_instruction *insn = (void *)p - p->offset; + u32 lu12iw, ori, lu32id, lu52id; + + lu12iw = (v >> 12) & 0xfffff; + ori = v & 0xfff; + lu32id = (v >> 32) & 0xfffff; + lu52id = v >> 52; + + insn[0].reg1i20_format.immediate = lu12iw; + insn[1].reg2i12_format.immediate = ori; + insn[2].reg1i20_format.immediate = lu32id; + insn[3].reg2i12_format.immediate = lu52id; + } +} + +void __init relocate_kernel(void) +{ + reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS; + + if (reloc_offset) + relocate_relative(); + + relocate_la_abs(); +} + +/* + * Show relocation information on panic. + */ +static void show_kernel_relocation(const char *level) +{ + if (reloc_offset > 0) { + printk(level); + pr_cont("Kernel relocated offset @ 0x%lx\n", reloc_offset); + pr_cont(" .text @ 0x%lx\n", (unsigned long)&_text); + pr_cont(" .data @ 0x%lx\n", (unsigned long)&_sdata); + pr_cont(" .bss @ 0x%lx\n", (unsigned long)&__bss_start); + } +} + +static int kernel_location_notifier_fn(struct notifier_block *self, + unsigned long v, void *p) +{ + show_kernel_relocation(KERN_EMERG); + return NOTIFY_DONE; +} + +static struct notifier_block kernel_location_notifier = { + .notifier_call = kernel_location_notifier_fn +}; + +static int __init register_kernel_offset_dumper(void) +{ + atomic_notifier_chain_register(&panic_notifier_list, + &kernel_location_notifier); + return 0; +} + +arch_initcall(register_kernel_offset_dumper); diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S index 733b16e8d55d..5ec0c008f01d 100644 --- a/arch/loongarch/kernel/vmlinux.lds.S +++ b/arch/loongarch/kernel/vmlinux.lds.S @@ -66,10 +66,21 @@ SECTIONS __alt_instructions_end = .; } +#ifdef CONFIG_RELOCATABLE + . = ALIGN(8); + .la_abs : AT(ADDR(.la_abs) - LOAD_OFFSET) { + __la_abs_begin = .; + *(.la_abs) + __la_abs_end = .; + } +#endif + .got : ALIGN(16) { *(.got) } .plt : ALIGN(16) { *(.plt) } .got.plt : ALIGN(16) { *(.got.plt) } + .data.rel : { *(.data.rel*) } + . = ALIGN(PECOFF_SEGMENT_ALIGN); __init_begin = .; __inittext_begin = .; @@ -93,8 +104,6 @@ SECTIONS PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT) #endif - .rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) } - .init.bss : { *(.init.bss) } @@ -107,6 +116,12 @@ SECTIONS RO_DATA(4096) RW_DATA(1 << CONFIG_L1_CACHE_SHIFT, PAGE_SIZE, THREAD_SIZE) + .rela.dyn : ALIGN(8) { + __rela_dyn_start = .; + *(.rela.dyn) *(.rela*) + __rela_dyn_end = .; + } + .sdata : { *(.sdata) } @@ -133,6 +148,7 @@ SECTIONS DISCARDS /DISCARD/ : { + *(.dynamic .dynsym .dynstr .hash .gnu.hash) *(.gnu.attributes) *(.options) *(.eh_frame) -- 2.37.3
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