Messages in this thread | | | Subject | Re: [PATCH 3/4] LoongArch: Add support for kernel relocation | From | Youling Tang <> | Date | Wed, 11 Jan 2023 11:18:51 +0800 |
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On 01/09/2023 05:07 PM, Youling Tang wrote: > arch/loongarch/kernel/relocate.c contains the functions necessary to > relocate the kernel elsewhere in memory. > > The kernel makes a copy of itself at the new address. It uses the > relocation table inserted by the relocs tool to fix symbol references > within the new image. > > If copy/relocation is successful then the entry point of the new kernel > is returned, otherwise fall back to starting the kernel in place. > > Signed-off-by: Youling Tang <tangyouling@loongson.cn> > --- > arch/loongarch/Kconfig | 15 +++++ > arch/loongarch/Makefile | 5 ++ > arch/loongarch/kernel/Makefile | 2 + > arch/loongarch/kernel/head.S | 18 ++++++ > arch/loongarch/kernel/relocate.c | 96 +++++++++++++++++++++++++++++ > arch/loongarch/kernel/vmlinux.lds.S | 11 +++- > 6 files changed, 145 insertions(+), 2 deletions(-) > create mode 100644 arch/loongarch/kernel/relocate.c > > diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig > index 9cc8b84f7eb0..089a4695b1b3 100644 > --- a/arch/loongarch/Kconfig > +++ b/arch/loongarch/Kconfig > @@ -48,6 +48,7 @@ config LOONGARCH > select ARCH_SUPPORTS_ATOMIC_RMW > select ARCH_SUPPORTS_HUGETLBFS > select ARCH_SUPPORTS_NUMA_BALANCING > + select SYS_SUPPORTS_RELOCATABLE > select ARCH_USE_BUILTIN_BSWAP > select ARCH_USE_CMPXCHG_LOCKREF > select ARCH_USE_QUEUED_RWLOCKS > @@ -229,6 +230,11 @@ config SCHED_OMIT_FRAME_POINTER > config AS_HAS_EXPLICIT_RELOCS > def_bool $(as-instr,x:pcalau12i \$t0$(comma)%pc_hi20(x)) > > +config SYS_SUPPORTS_RELOCATABLE > + bool > + help > + Selected if the platform supports relocating the kernel. > + > menu "Kernel type and options" > > source "kernel/Kconfig.hz" > @@ -474,6 +480,15 @@ config PHYSICAL_START > specified in the "crashkernel=YM@XM" command line boot parameter > passed to the panic-ed kernel). > > +config RELOCATABLE > + bool "Relocatable kernel" > + depends on SYS_SUPPORTS_RELOCATABLE > + 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 4402387d2755..27b5a70ff31c 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 += $(call cc-option, -mno-check-zero-division) > > diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile > index fcaa024a685e..33787d22e6f4 100644 > --- a/arch/loongarch/kernel/Makefile > +++ b/arch/loongarch/kernel/Makefile > @@ -31,6 +31,8 @@ endif > obj-$(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 e8a4bf9d7599..6db1549177ad 100644 > --- a/arch/loongarch/kernel/head.S > +++ b/arch/loongarch/kernel/head.S > @@ -88,7 +88,25 @@ SYM_CODE_START(kernel_entry) # kernel entry point > PTR_ADD sp, sp, tp > set_saved_sp sp, t0, t1 > > +#ifdef CONFIG_RELOCATABLE > + /* Copy kernel and apply the relocations */ > + bl relocate_kernel > + > + /* Repoint the sp into the new kernel image */ > + PTR_LI sp, (_THREAD_SIZE - 32 - PT_SIZE) > + PTR_ADD sp, sp, tp > + set_saved_sp sp, t0, t1 > + PTR_ADDI sp, sp, -4 * SZREG # init stack pointer PTR_ADDI sp, sp, -4 * SZREG # init stack pointer
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> + > + /* > + * relocate_kernel returns the entry point either > + * in the relocated kernel or the original if for > + * some reason relocation failed. > + */ > + jr a0 > +#else > bl start_kernel > +#endif > ASM_BUG() > > SYM_CODE_END(kernel_entry) > diff --git a/arch/loongarch/kernel/relocate.c b/arch/loongarch/kernel/relocate.c > new file mode 100644 > index 000000000000..a58551c0698d > --- /dev/null > +++ b/arch/loongarch/kernel/relocate.c > @@ -0,0 +1,96 @@ > +// 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/start_kernel.h> > +#include <linux/printk.h> > +#include <linux/panic_notifier.h> > +#include <asm/bootinfo.h> > +#include <asm/inst.h> > +#include <asm/sections.h> > + > +#define RELOCATED(x) ((void *)((long)x + offset)) > + > +extern long __rela_dyn_start; > +extern long __rela_dyn_end; > + > +/* > + * Choose a new address for the kernel, for now we'll hard > + * code the destination. > + */ > +static inline void __init *determine_relocation_address(void) > +{ > + return (void *)(CACHE_BASE + 0x02000000); > +} > + > +static inline int __init relocation_addr_valid(void *loc_new) > +{ > + if ((unsigned long)loc_new & 0x0000ffff) { > + /* Inappropriately aligned new location */ > + return 0; > + } > + if ((unsigned long)loc_new < (unsigned long)_end) { > + /* New location overlaps original kernel */ > + return 0; > + } > + return 1; > +} > + > +void *__init relocate_kernel(void) > +{ > + Elf64_Rela *rela, *rela_end; > + void *loc_new; > + unsigned long kernel_length; > + long offset = 0; > + int res = 1; > + /* Default to original kernel entry point */ > + void *kernel_entry = start_kernel; > + > + kernel_length = (long)(_end) - (long)(_text); > + > + loc_new = determine_relocation_address(); > + > + /* Sanity check relocation address */ > + if (relocation_addr_valid(loc_new)) > + offset = (unsigned long)loc_new - (unsigned long)(_text); > + > + if (offset) { > + /* Copy the kernel to it's new location */ > + memcpy(loc_new, _text, kernel_length); > + > + /* Sync the caches ready for execution of new kernel */ > + __asm__ __volatile__ ( > + "ibar 0 \t\n" > + "dbar 0 \t\n"); > + > + rela = (Elf64_Rela *)RELOCATED(&__rela_dyn_start); > + rela_end = (Elf64_Rela *)RELOCATED(&__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 = RELOCATED(relocated_addr); > + > + *(Elf64_Addr *)RELOCATED(addr) = relocated_addr; > + > + } > + > + /* The current thread is now within the relocated image */ > + __current_thread_info = RELOCATED(__current_thread_info); > + > + /* Return the new kernel's entry point */ > + kernel_entry = RELOCATED(start_kernel); > + } > +out: > + return kernel_entry; > +} > diff --git a/arch/loongarch/kernel/vmlinux.lds.S b/arch/loongarch/kernel/vmlinux.lds.S > index 733b16e8d55d..aec0b6567d24 100644 > --- a/arch/loongarch/kernel/vmlinux.lds.S > +++ b/arch/loongarch/kernel/vmlinux.lds.S > @@ -70,6 +70,8 @@ SECTIONS > .plt : ALIGN(16) { *(.plt) } > .got.plt : ALIGN(16) { *(.got.plt) } > > + .data.rel : { *(.data.rel*) } > + > . = ALIGN(PECOFF_SEGMENT_ALIGN); > __init_begin = .; > __inittext_begin = .; > @@ -93,8 +95,6 @@ SECTIONS > PERCPU_SECTION(1 << CONFIG_L1_CACHE_SHIFT) > #endif > > - .rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) } > - > .init.bss : { > *(.init.bss) > } > @@ -107,6 +107,12 @@ 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 +139,7 @@ SECTIONS > > DISCARDS > /DISCARD/ : { > + *(.dynamic .dynsym .dynstr .hash .gnu.hash) > *(.gnu.attributes) > *(.options) > *(.eh_frame) >
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