s390/kernel: build a relocatable kernel

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>

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 21e851b..4c99e4f 100644 (file)
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -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"

diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index 9c079a5..54b8a12 100644 (file)
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -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))

diff --git a/arch/s390/boot/Makefile b/arch/s390/boot/Makefile
index c1993c5..4df43e8 100644 (file)
--- a/arch/s390/boot/Makefile
+++ b/arch/s390/boot/Makefile
@@ -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
 

diff --git a/arch/s390/boot/compressed/decompressor.h b/arch/s390/boot/compressed/decompressor.h
index 424cf52..c15eb71 100644 (file)
--- a/arch/s390/boot/compressed/decompressor.h
+++ b/arch/s390/boot/compressed/decompressor.h
@@ -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[];

diff --git a/arch/s390/boot/machine_kexec_reloc.c b/arch/s390/boot/machine_kexec_reloc.c
new file mode 100644 (file)
index 0000000..b7a5d0f
--- /dev/null
+++ b/arch/s390/boot/machine_kexec_reloc.c
@@ -0,0 +1,2 @@
+// SPDX-License-Identifier: GPL-2.0
+#include "../kernel/machine_kexec_reloc.c"

diff --git a/arch/s390/boot/startup.c b/arch/s390/boot/startup.c
index 9089897..b7d6a76 100644 (file)
--- a/arch/s390/boot/startup.c
+++ b/arch/s390/boot/startup.c
@@ -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();
 }

diff --git a/arch/s390/include/asm/kexec.h b/arch/s390/include/asm/kexec.h
index 305d346..ea398a0 100644 (file)
--- a/arch/s390/include/asm/kexec.h
+++ b/arch/s390/include/asm/kexec.h
@@ -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;

diff --git a/arch/s390/kernel/Makefile b/arch/s390/kernel/Makefile
index d28acd7..1942560 100644 (file)
--- a/arch/s390/kernel/Makefile
+++ b/arch/s390/kernel/Makefile
@@ -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
 

diff --git a/arch/s390/kernel/machine_kexec_file.c b/arch/s390/kernel/machine_kexec_file.c
index 48cab96..42c23a5 100644 (file)
--- a/arch/s390/kernel/machine_kexec_file.c
+++ b/arch/s390/kernel/machine_kexec_file.c
@@ -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;
 }

diff --git a/arch/s390/kernel/machine_kexec_reloc.c b/arch/s390/kernel/machine_kexec_reloc.c
new file mode 100644 (file)
index 0000000..1dded39
--- /dev/null
+++ b/arch/s390/kernel/machine_kexec_reloc.c
@@ -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;
+}

diff --git a/arch/s390/kernel/vmlinux.lds.S b/arch/s390/kernel/vmlinux.lds.S
index 6ef9c62..49d5532 100644 (file)
--- a/arch/s390/kernel/vmlinux.lds.S
+++ b/arch/s390/kernel/vmlinux.lds.S
@@ -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.  */