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s390/kernel: build a relocatable kernel

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This patch adds support for building a relocatable kernel with -fPIE.
The kernel will be relocated to 0 early in the boot process.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
This commit is contained in:
Gerald Schaefer 2019-02-03 21:35:45 +01:00 committed by Martin Schwidefsky
parent 833b441ec0
commit 805bc0bc23
11 changed files with 124 additions and 42 deletions
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13
arch/s390/Kconfig
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@ -624,6 +624,19 @@ config EXPOLINE_FULL
endchoice
config RELOCATABLE
bool "Build a relocatable kernel"
select MODULE_REL_CRCS if MODVERSIONS
default y
help
This builds a kernel image that retains relocation information
so it can be loaded at an arbitrary address.
The kernel is linked as a position-independent executable (PIE)
and contains dynamic relocations which are processed early in the
bootup process.
The relocations make the kernel image about 15% larger (compressed
10%), but are discarded at runtime.
endmenu
menu "Memory setup"

4
arch/s390/Makefile
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@ -16,6 +16,10 @@ KBUILD_AFLAGS_MODULE += -fPIC
KBUILD_CFLAGS_MODULE += -fPIC
KBUILD_AFLAGS += -m64
KBUILD_CFLAGS += -m64
ifeq ($(CONFIG_RELOCATABLE),y)
KBUILD_CFLAGS += -fPIE
LDFLAGS_vmlinux := -pie
endif
aflags_dwarf := -Wa,-gdwarf-2
KBUILD_AFLAGS_DECOMPRESSOR := -m64 -D__ASSEMBLY__
KBUILD_AFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),$(aflags_dwarf))

1
arch/s390/boot/Makefile
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@ -32,6 +32,7 @@ obj-y := head.o als.o startup.o mem_detect.o ipl_parm.o ipl_report.o
obj-y += string.o ebcdic.o sclp_early_core.o mem.o ipl_vmparm.o cmdline.o
obj-y += ctype.o
obj-$(CONFIG_PROTECTED_VIRTUALIZATION_GUEST) += uv.o
obj-$(CONFIG_RELOCATABLE) += machine_kexec_reloc.o
targets := bzImage startup.a section_cmp.boot.data section_cmp.boot.preserved.data $(obj-y)
subdir- := compressed

3
arch/s390/boot/compressed/decompressor.h
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@ -19,6 +19,9 @@ struct vmlinux_info {
unsigned long bootdata_size;
unsigned long bootdata_preserved_off;
unsigned long bootdata_preserved_size;
unsigned long dynsym_start;
unsigned long rela_dyn_start;
unsigned long rela_dyn_end;
};
extern char _vmlinux_info[];

2
arch/s390/boot/machine_kexec_reloc.c Normal file
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@ -0,0 +1,2 @@
// SPDX-License-Identifier: GPL-2.0
#include "../kernel/machine_kexec_reloc.c"

27
arch/s390/boot/startup.c
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@ -1,6 +1,8 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/string.h>
#include <linux/elf.h>
#include <asm/setup.h>
#include <asm/kexec.h>
#include <asm/sclp.h>
#include <asm/uv.h>
#include "compressed/decompressor.h"
@ -47,6 +49,29 @@ static void copy_bootdata(void)
memcpy((void *)vmlinux.bootdata_preserved_off, __boot_data_preserved_start, vmlinux.bootdata_preserved_size);
}
static void handle_relocs(unsigned long offset)
{
Elf64_Rela *rela_start, *rela_end, *rela;
int r_type, r_sym, rc;
Elf64_Addr loc, val;
Elf64_Sym *dynsym;
rela_start = (Elf64_Rela *) vmlinux.rela_dyn_start;
rela_end = (Elf64_Rela *) vmlinux.rela_dyn_end;
dynsym = (Elf64_Sym *) vmlinux.dynsym_start;
for (rela = rela_start; rela < rela_end; rela++) {
loc = rela->r_offset + offset;
val = rela->r_addend + offset;
r_sym = ELF64_R_SYM(rela->r_info);
if (r_sym)
val += dynsym[r_sym].st_value;
r_type = ELF64_R_TYPE(rela->r_info);
rc = arch_kexec_do_relocs(r_type, (void *) loc, val, 0);
if (rc)
error("Unknown relocation type");
}
}
void startup_kernel(void)
{
unsigned long safe_addr;
@ -67,5 +92,7 @@ void startup_kernel(void)
memmove((void *)vmlinux.default_lma, img, vmlinux.image_size);
}
copy_bootdata();
if (IS_ENABLED(CONFIG_RELOCATABLE))
handle_relocs(0);
vmlinux.entry();
}

2
arch/s390/include/asm/kexec.h
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@ -71,6 +71,8 @@ int s390_verify_sig(const char *kernel, unsigned long kernel_len);
void *kexec_file_add_components(struct kimage *image,
int (*add_kernel)(struct kimage *image,
struct s390_load_data *data));
int arch_kexec_do_relocs(int r_type, void *loc, unsigned long val,
unsigned long addr);
extern const struct kexec_file_ops s390_kexec_image_ops;
extern const struct kexec_file_ops s390_kexec_elf_ops;

2
arch/s390/kernel/Makefile
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@ -51,7 +51,7 @@ obj-y += debug.o irq.o ipl.o dis.o diag.o vdso.o early_nobss.o
obj-y += sysinfo.o lgr.o os_info.o machine_kexec.o pgm_check.o
obj-y += runtime_instr.o cache.o fpu.o dumpstack.o guarded_storage.o sthyi.o
obj-y += entry.o reipl.o relocate_kernel.o kdebugfs.o alternative.o
obj-y += nospec-branch.o ipl_vmparm.o
obj-y += nospec-branch.o ipl_vmparm.o machine_kexec_reloc.o
extra-y += head64.o vmlinux.lds

44
arch/s390/kernel/machine_kexec_file.c
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@ -290,7 +290,7 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
const Elf_Shdr *symtab)
{
Elf_Rela *relas;
int i;
int i, r_type;
relas = (void *)pi->ehdr + relsec->sh_offset;
@ -324,46 +324,8 @@ int arch_kexec_apply_relocations_add(struct purgatory_info *pi,
addr = section->sh_addr + relas[i].r_offset;
switch (ELF64_R_TYPE(relas[i].r_info)) {
case R_390_8: /* Direct 8 bit. */
*(u8 *)loc = val;
break;
case R_390_12: /* Direct 12 bit. */
*(u16 *)loc &= 0xf000;
*(u16 *)loc |= val & 0xfff;
break;
case R_390_16: /* Direct 16 bit. */
*(u16 *)loc = val;
break;
case R_390_20: /* Direct 20 bit. */
*(u32 *)loc &= 0xf00000ff;
*(u32 *)loc |= (val & 0xfff) << 16; /* DL */
*(u32 *)loc |= (val & 0xff000) >> 4; /* DH */
break;
case R_390_32: /* Direct 32 bit. */
*(u32 *)loc = val;
break;
case R_390_64: /* Direct 64 bit. */
*(u64 *)loc = val;
break;
case R_390_PC16: /* PC relative 16 bit. */
*(u16 *)loc = (val - addr);
break;
case R_390_PC16DBL: /* PC relative 16 bit shifted by 1. */
*(u16 *)loc = (val - addr) >> 1;
break;
case R_390_PC32DBL: /* PC relative 32 bit shifted by 1. */
*(u32 *)loc = (val - addr) >> 1;
break;
case R_390_PC32: /* PC relative 32 bit. */
*(u32 *)loc = (val - addr);
break;
case R_390_PC64: /* PC relative 64 bit. */
*(u64 *)loc = (val - addr);
break;
default:
break;
}
r_type = ELF64_R_TYPE(relas[i].r_info);
arch_kexec_do_relocs(r_type, loc, val, addr);
}
return 0;
}

53
arch/s390/kernel/machine_kexec_reloc.c Normal file
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@ -0,0 +1,53 @@
// SPDX-License-Identifier: GPL-2.0
#include <linux/elf.h>
int arch_kexec_do_relocs(int r_type, void *loc, unsigned long val,
unsigned long addr)
{
switch (r_type) {
case R_390_NONE:
break;
case R_390_8: /* Direct 8 bit. */
*(u8 *)loc = val;
break;
case R_390_12: /* Direct 12 bit. */
*(u16 *)loc &= 0xf000;
*(u16 *)loc |= val & 0xfff;
break;
case R_390_16: /* Direct 16 bit. */
*(u16 *)loc = val;
break;
case R_390_20: /* Direct 20 bit. */
*(u32 *)loc &= 0xf00000ff;
*(u32 *)loc |= (val & 0xfff) << 16; /* DL */
*(u32 *)loc |= (val & 0xff000) >> 4; /* DH */
break;
case R_390_32: /* Direct 32 bit. */
*(u32 *)loc = val;
break;
case R_390_64: /* Direct 64 bit. */
*(u64 *)loc = val;
break;
case R_390_PC16: /* PC relative 16 bit. */
*(u16 *)loc = (val - addr);
break;
case R_390_PC16DBL: /* PC relative 16 bit shifted by 1. */
*(u16 *)loc = (val - addr) >> 1;
break;
case R_390_PC32DBL: /* PC relative 32 bit shifted by 1. */
*(u32 *)loc = (val - addr) >> 1;
break;
case R_390_PC32: /* PC relative 32 bit. */
*(u32 *)loc = (val - addr);
break;
case R_390_PC64: /* PC relative 64 bit. */
*(u64 *)loc = (val - addr);
break;
case R_390_RELATIVE:
*(unsigned long *) loc = val;
break;
default:
return 1;
}
return 0;
}

15
arch/s390/kernel/vmlinux.lds.S
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@ -144,6 +144,18 @@ SECTIONS
INIT_DATA_SECTION(0x100)
PERCPU_SECTION(0x100)
.dynsym ALIGN(8) : {
__dynsym_start = .;
*(.dynsym)
__dynsym_end = .;
}
.rela.dyn ALIGN(8) : {
__rela_dyn_start = .;
*(.rela*)
__rela_dyn_end = .;
}
. = ALIGN(PAGE_SIZE);
__init_end = .; /* freed after init ends here */
@ -165,6 +177,9 @@ SECTIONS
QUAD(__boot_data_preserved_start) /* bootdata_preserved_off */
QUAD(__boot_data_preserved_end -
__boot_data_preserved_start) /* bootdata_preserved_size */
QUAD(__dynsym_start) /* dynsym_start */
QUAD(__rela_dyn_start) /* rela_dyn_start */
QUAD(__rela_dyn_end) /* rela_dyn_end */
} :NONE
/* Debugging sections. */