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>

11 files changed, 124 insertions, 42 deletions

diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 21e851b0a989..4c99e4f5f366 100644
--- 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 9c079a506325..54b8a12d64e8 100644
--- 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 c1993c57300f..4df43e83363a 100644
--- 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 424cf524aac1..c15eb7114d83 100644
--- 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
index 000000000000..b7a5d0f72097
--- /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 90898976a941..b7d6a76cb5e9 100644
--- 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 305d3465574f..ea398a05f643 100644
--- 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 d28acd7ba81e..19425605a83d 100644
--- 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 48cab9600ed9..42c23a5c8229 100644
--- 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
index 000000000000..1dded39239f8
--- /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 6ef9c62bb01b..49d55327de0b 100644
--- 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.  */