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Message-ID: <3b281ec1-c432-eb7b-3131-3049a0d0ea95@loongson.cn>
Date: Wed, 11 Jan 2023 11:18:51 +0800
From: Youling Tang <tangyouling@...ngson.cn>
To: Huacai Chen <chenhuacai@...nel.org>,
Xi Ruoyao <xry111@...111.site>,
Jinyang He <hejinyang@...ngson.cn>
Cc: Xuerui Wang <kernel@...0n.name>, loongarch@...ts.linux.dev,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] LoongArch: Add support for kernel relocation
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@...ngson.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
This line needs to be removed.
> +
> + /*
> + * 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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