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[PATCH v4 4/5] LoongArch: Add support for kernel relocation

Youling Tang posted 5 patches 2 years, 7 months ago
There is a newer version of this series
[PATCH v4 4/5] LoongArch: Add support for kernel relocation
Posted by Youling Tang 2 years, 7 months ago 
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
---
 arch/loongarch/Kconfig              | 15 ++++++
 arch/loongarch/Makefile             |  5 ++
 arch/loongarch/kernel/Makefile      |  2 +
 arch/loongarch/kernel/head.S        |  5 ++
 arch/loongarch/kernel/relocate.c    | 78 +++++++++++++++++++++++++++++
 arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
 6 files changed, 114 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 c8cfbd562921..3341dd5f0926 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..91ce92433bab
--- /dev/null
+++ b/arch/loongarch/kernel/relocate.c
@@ -0,0 +1,78 @@
+// 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/sections.h>
+
+#define RELOCATED(x) ((void *)((long)x + reloc_offset))
+
+extern long __rela_dyn_start;
+extern long __rela_dyn_end;
+
+static unsigned long reloc_offset;
+
+void __init relocate_kernel(void)
+{
+	reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
+
+	if (reloc_offset) {
+		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;
+		}
+	}
+}
+
+/*
+ * 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..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)
-- 
2.37.3
Re: [PATCH v4 4/5] LoongArch: Add support for kernel relocation
Posted by kernel test robot 2 years, 7 months ago 
Hi Youling,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on linus/master]
[also build test WARNING on v6.2-rc7 next-20230210]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Youling-Tang/LoongArch-Use-la-pcrel-instead-of-la-abs-when-it-s-trivially-possible/20230210-165022
patch link:    https://lore.kernel.org/r/1676018856-26520-5-git-send-email-tangyouling%40loongson.cn
patch subject: [PATCH v4 4/5] LoongArch: Add support for kernel relocation
config: loongarch-allmodconfig (https://download.01.org/0day-ci/archive/20230211/202302110150.tIuRIiTp-lkp@intel.com/config)
compiler: loongarch64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/26dc7750408c7f232632db44fab905df7b48d83c
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Youling-Tang/LoongArch-Use-la-pcrel-instead-of-la-abs-when-it-s-trivially-possible/20230210-165022
        git checkout 26dc7750408c7f232632db44fab905df7b48d83c
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=loongarch SHELL=/bin/bash arch/loongarch/kernel/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202302110150.tIuRIiTp-lkp@intel.com/

Note: functions only called from assembly code should be annotated with the asmlinkage attribute
All warnings (new ones prefixed by >>):

>> arch/loongarch/kernel/relocate.c:21:13: warning: no previous prototype for 'relocate_kernel' [-Wmissing-prototypes]
      21 | void __init relocate_kernel(void)
         |             ^~~~~~~~~~~~~~~


vim +/relocate_kernel +21 arch/loongarch/kernel/relocate.c

    20	
  > 21	void __init relocate_kernel(void)
    22	{
    23		reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
    24	
    25		if (reloc_offset) {
    26			Elf64_Rela *rela, *rela_end;
    27			rela = (Elf64_Rela *)&__rela_dyn_start;
    28			rela_end = (Elf64_Rela *)&__rela_dyn_end;
    29	
    30			for ( ; rela < rela_end; rela++) {
    31				Elf64_Addr addr = rela->r_offset;
    32				Elf64_Addr relocated_addr = rela->r_addend;
    33	
    34				if (rela->r_info != R_LARCH_RELATIVE)
    35					continue;
    36	
    37				if (relocated_addr >= VMLINUX_LOAD_ADDRESS)
    38					relocated_addr =
    39						(Elf64_Addr)RELOCATED(relocated_addr);
    40	
    41				*(Elf64_Addr *)RELOCATED(addr) = relocated_addr;
    42			}
    43		}
    44	}
    45	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests
Re: [PATCH v4 4/5] LoongArch: Add support for kernel relocation
Posted by Huacai Chen 2 years, 7 months ago 
Hi, Youling,

On Fri, Feb 10, 2023 at 4:48 PM Youling Tang <tangyouling@loongson.cn> wrote:
>
> 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
> ---
>  arch/loongarch/Kconfig              | 15 ++++++
>  arch/loongarch/Makefile             |  5 ++
>  arch/loongarch/kernel/Makefile      |  2 +
>  arch/loongarch/kernel/head.S        |  5 ++
>  arch/loongarch/kernel/relocate.c    | 78 +++++++++++++++++++++++++++++
>  arch/loongarch/kernel/vmlinux.lds.S | 11 +++-
>  6 files changed, 114 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
We don't need such a Kconfig option since it is always true.

Huacai
>         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 += $(call cc-option, -mno-check-zero-division)
>
> diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
> index c8cfbd562921..3341dd5f0926 100644
> --- a/arch/loongarch/kernel/Makefile
> +++ b/arch/loongarch/kernel/Makefile
> @@ -31,6 +31,8 @@ endif
>  obj-$(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..91ce92433bab
> --- /dev/null
> +++ b/arch/loongarch/kernel/relocate.c
> @@ -0,0 +1,78 @@
> +// 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/sections.h>
> +
> +#define RELOCATED(x) ((void *)((long)x + reloc_offset))
> +
> +extern long __rela_dyn_start;
> +extern long __rela_dyn_end;
> +
> +static unsigned long reloc_offset;
> +
> +void __init relocate_kernel(void)
> +{
> +       reloc_offset = (unsigned long)_text - VMLINUX_LOAD_ADDRESS;
> +
> +       if (reloc_offset) {
> +               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;
> +               }
> +       }
> +}
> +
> +/*
> + * 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..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)
> --
> 2.37.3
>

Patchew 2.1-devel-b67e4c2

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