[PATCH 2/3] LoongArch: Add support for kernel relocation
From: Youling Tang
Date: Fri Sep 02 2022 - 06:09:29 EST
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@xxxxxxxxxxx>
---
arch/loongarch/Kconfig | 29 ++++
arch/loongarch/Makefile | 7 +
arch/loongarch/Makefile.postlink | 33 +++++
arch/loongarch/kernel/Makefile | 2 +
arch/loongarch/kernel/head.S | 17 +++
arch/loongarch/kernel/relocate.c | 214 ++++++++++++++++++++++++++++
arch/loongarch/kernel/vmlinux.lds.S | 25 ++++
7 files changed, 327 insertions(+)
create mode 100644 arch/loongarch/Makefile.postlink
create mode 100644 arch/loongarch/kernel/relocate.c
diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
index 0721b4b2207a..271221d6036d 100644
--- a/arch/loongarch/Kconfig
+++ b/arch/loongarch/Kconfig
@@ -47,6 +47,7 @@ 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
@@ -207,6 +208,11 @@ 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"
@@ -420,6 +426,29 @@ config ARCH_IOREMAP
protection support. However, you can enable LoongArch DMW-based
ioremap() for better performance.
+config RELOCATABLE
+ bool "Relocatable kernel"
+ depends on SYS_SUPPORTS_RELOCATABLE
+ help
+ This builds a kernel image that retains relocation information
+ so it can be loaded someplace besides the default 1MB.
+
+config RELOCATION_TABLE_SIZE
+ hex "Relocation table size"
+ depends on RELOCATABLE
+ range 0x0 0x01000000
+ default "0x00100000"
+ help
+ A table of relocation data will be appended to the kernel binary
+ and parsed at boot to fix up the relocated kernel.
+
+ This option allows the amount of space reserved for the table to be
+ adjusted, although the default of 1Mb should be ok in most cases.
+
+ The build will fail and a valid size suggested if this is too small.
+
+ If unsure, leave at the default value.
+
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 92c4a52c4c3e..01773114960e 100644
--- a/arch/loongarch/Makefile
+++ b/arch/loongarch/Makefile
@@ -62,12 +62,19 @@ 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 += --emit-relocs
+endif
+
cflags-y += -ffreestanding
cflags-y += $(call cc-option, -mno-check-zero-division)
load-y = 0x9000000000200000
bootvars-y = VMLINUX_LOAD_ADDRESS=$(load-y)
+archscripts: scripts_basic
+ $(Q)$(MAKE) $(build)=arch/loongarch/boot/tools relocs
+
drivers-$(CONFIG_PCI) += arch/loongarch/pci/
KBUILD_AFLAGS += $(cflags-y)
diff --git a/arch/loongarch/Makefile.postlink b/arch/loongarch/Makefile.postlink
new file mode 100644
index 000000000000..2b3576d26cb6
--- /dev/null
+++ b/arch/loongarch/Makefile.postlink
@@ -0,0 +1,33 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Insert relocations into vmlinux
+
+PHONY := __archpost
+__archpost:
+
+-include include/config/auto.conf
+include scripts/Kbuild.include
+
+CMD_RELOCS = arch/loongarch/boot/tools/relocs --keep
+quiet_cmd_relocs = RELOCS $@
+ cmd_relocs = $(CMD_RELOCS) $@
+
+# `@true` prevents complaint when there is nothing to be done
+
+vmlinux: FORCE
+ @true
+ifeq ($(CONFIG_RELOCATABLE),y)
+ $(call if_changed,relocs)
+endif
+
+%.ko: FORCE
+ @true
+
+clean:
+ @true
+
+PHONY += FORCE clean
+
+FORCE:
+
+.PHONY: $(PHONY)
diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 7225916dd378..2998b7d4555d 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -17,6 +17,8 @@ obj-$(CONFIG_CPU_HAS_FPU) += fpu.o
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 eb3f641d5915..74b83e357d49 100644
--- a/arch/loongarch/kernel/head.S
+++ b/arch/loongarch/kernel/head.S
@@ -79,8 +79,25 @@ SYM_CODE_START(kernel_entry) # kernel entry point
PTR_ADD sp, sp, tp
set_saved_sp sp, t0, t1
PTR_ADDI sp, sp, -4 * SZREG # init stack pointer
+#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
+
+ /*
+ * 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
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..492c833322a4
--- /dev/null
+++ b/arch/loongarch/kernel/relocate.c
@@ -0,0 +1,214 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for Kernel relocation at boot time
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ *
+ * Derived from MIPS:
+ * Copyright (C) 2015, Imagination Technologies Ltd.
+ */
+
+#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 u32 __start_relocation[]; /* Start relocation table */
+extern u32 __stop_relocation[]; /* End relocation table */
+
+extern long __start___ex_table[]; /* Start exception table */
+extern long __stop___ex_table[]; /* End exception table */
+
+extern long __start_got[]; /* Start GOT table */
+extern long __stop_got[]; /* End GOT table */
+
+static void __init apply_r_loongarch_64_rel(u32 *loc_new, long offset)
+{
+ *(u64 *)loc_new += offset;
+}
+
+/*
+ * The details about la.abs r1, imm64
+ *
+ * lu12i.w $r1, 0
+ * ori $r1, $r1, 0
+ * lu32i.d $r1, 0
+ * lu52i.d $r1, $r1, 0
+ *
+ * LoongArch use lu12i.w, ori, lu32i.d, lu52i.d to load a 64bit imm.
+ * lu12i.w load bit31~bit12, ori load bit11~bit0,
+ * lu32i.d load bit51~bit32, lu52i.d load bit63~bit52
+ */
+
+static void __init apply_r_loongarch_la_rel(u32 *loc_new, long offset)
+{
+ unsigned long long dest;
+ union loongarch_instruction *ori, *lu12iw, *lu32id, *lu52id;
+
+ ori = (union loongarch_instruction *)&loc_new[1];
+ lu12iw = (union loongarch_instruction *)&loc_new[0];
+ lu32id = (union loongarch_instruction *)&loc_new[2];
+ lu52id = (union loongarch_instruction *)&loc_new[3];
+
+ dest = ori->reg2i12_format.immediate & 0xfff;
+ dest |= (lu12iw->reg1i20_format.immediate & 0xfffff) << 12;
+ dest |= ((u64)lu32id->reg1i20_format.immediate & 0xfffff) << 32;
+ dest |= ((u64)lu52id->reg2i12_format.immediate & 0xfff) << 52;
+ dest += offset;
+
+ ori->reg2i12_format.immediate = dest & 0xfff;
+ lu12iw->reg1i20_format.immediate = (dest >> 12) & 0xfffff;
+ lu32id->reg1i20_format.immediate = (dest >> 32) & 0xfffff;
+ lu52id->reg2i12_format.immediate = (dest >> 52) & 0xfff;
+}
+
+static int __init reloc_handler(u32 type, u32 *loc_new, long offset)
+{
+ switch (type) {
+ case 1:
+ apply_r_loongarch_64_rel(loc_new, offset);
+ break;
+ case 2:
+ apply_r_loongarch_la_rel(loc_new, offset);
+ break;
+ default:
+ pr_err("Unhandled relocation type %d\n", type);
+ return -ENOEXEC;
+ }
+
+ return 0;
+
+}
+
+static int __init do_relocations(void *kbase_new, long offset, u32 *rstart, u32 *rend)
+{
+ u32 *r;
+ u32 *loc_new;
+ int type;
+ int res;
+
+ /* r->offset is relative to _stext instead of _text */
+ kbase_new = (void *)((u64)kbase_new + (u64)_stext - (u64)_text);
+
+ for (r = rstart; r < rend; r++) {
+ /* Sentinel for last relocation */
+ if (*r == 0)
+ break;
+
+ type = (*r >> 28) & 0xf;
+ loc_new = (void *)(kbase_new + ((*r & 0x0fffffff) << 2));
+
+ res = reloc_handler(type, loc_new, offset);
+ if (res)
+ return res;
+
+ }
+
+ return 0;
+}
+
+/*
+ * The exception table is filled in by the relocs tool after vmlinux is linked.
+ * It must be relocated separately since there will not be any relocation
+ * information for it filled in by the linker.
+ */
+static void __init relocate_exception_table(long offset)
+{
+#ifdef CONFIG_BUILDTIME_TABLE_SORT
+ unsigned long *etable_start, *etable_end, *e;
+
+ etable_start = RELOCATED((unsigned long)__start___ex_table
+ - (unsigned long)_text + VMLINUX_LOAD_ADDRESS);
+ etable_end = RELOCATED((unsigned long)__stop___ex_table
+ - (unsigned long)_text + VMLINUX_LOAD_ADDRESS);
+
+ for (e = etable_start; e < etable_end; e++)
+ *e += offset;
+#endif
+}
+
+static void __init relocate_got_table(long offset)
+{
+ unsigned long *got_start, *got_end, *got;
+
+ got_start = RELOCATED((unsigned long)__start_got
+ - (unsigned long)_text + VMLINUX_LOAD_ADDRESS);
+ got_end = RELOCATED((unsigned long)__stop_got
+ - (unsigned long)_text + VMLINUX_LOAD_ADDRESS);
+
+ for (got = got_start + 1; got < got_end; got++)
+ *got += offset;
+}
+
+/*
+ * 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)
+{
+ 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");
+
+ /* Perform relocations on the new kernel */
+ res = do_relocations(loc_new, offset, __start_relocation,
+ __stop_relocation);
+ if (res < 0)
+ goto out;
+
+ relocate_exception_table(offset);
+ relocate_got_table(offset);
+
+ /* 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 e5890bec2bf6..512bf699c877 100644
--- a/arch/loongarch/kernel/vmlinux.lds.S
+++ b/arch/loongarch/kernel/vmlinux.lds.S
@@ -55,6 +55,12 @@ SECTIONS
EXCEPTION_TABLE(16)
+ .got : {
+ __start_got = .;
+ *(.got) /* Global offset table */
+ __stop_got = .;
+ }
+
. = ALIGN(PECOFF_SEGMENT_ALIGN);
__init_begin = .;
__inittext_begin = .;
@@ -80,6 +86,25 @@ SECTIONS
.rela.dyn : ALIGN(8) { *(.rela.dyn) *(.rela*) }
+#ifdef CONFIG_RELOCATABLE
+ . = ALIGN(4);
+ .data.reloc : {
+ __start_relocation = .;
+ /*
+ * Space for relocation table
+ * This needs to be filled so that the
+ * relocs tool can overwrite the content.
+ * An invalid value is left at the start of the
+ * section to abort relocation if the table
+ * has not been filled in.
+ */
+ LONG(0xFFFFFFFF);
+ FILL(0);
+ . += CONFIG_RELOCATION_TABLE_SIZE - 4;
+ __stop_relocation = .;
+ }
+#endif
+
.init.bss : {
*(.init.bss)
}
--
2.36.1