ARM: PIE: Add position independent executable embedding to ARM

Add support to ARM for embedding PIEs into the kernel, loading them into
genalloc pools (such as SRAM) and executing them. Support for ARM means
performing R_ARM_RELATIVE fixups within the .rel.dyn section.

Signed-off-by: Russ Dill <Russ.Dill@ti.com>

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 02b9bf9268dd95f1d712dff4285a3998c5f009df..2092322106d0731422cb089e8031d65046b39cf7 100644 (file)
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -47,6 +47,7 @@ config ARM
        select HAVE_MEMBLOCK
        select HAVE_OPROFILE if (HAVE_PERF_EVENTS)
        select HAVE_PERF_EVENTS
+       select HAVE_PIE
        select HAVE_REGS_AND_STACK_ACCESS_API
        select HAVE_SYSCALL_TRACEPOINTS
        select HAVE_UID16

diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 883e4bec807fe3614a767de19b21783e93b11cfd..4b5ff1e590ddc08011fe6402ab2a76e0f3d98bed 100644 (file)
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -121,6 +121,8 @@ KBUILD_AFLAGS       +=$(CFLAGS_ABI) $(AFLAGS_ISA) $(arch-y) $(tune-y) -include asm/uni
 
 CHECKFLAGS     += -D__arm__
 
+OBJCOPY_OUTPUT_FORMAT := elf32-littlearm
+
 #Default value
 head-y         := arch/arm/kernel/head$(MMUEXT).o
 textofs-y      := 0x00008000
@@ -261,6 +263,9 @@ drivers-$(CONFIG_OPROFILE)      += arch/arm/oprofile/
 
 libs-y                         := arch/arm/lib/ $(libs-y)
 
+PIE_LDS                                := arch/arm/kernel/pie.lds
+libpie-$(CONFIG_PIE)           += arch/arm/libpie/
+
 # Default target when executing plain make
 ifeq ($(CONFIG_XIP_KERNEL),y)
 KBUILD_IMAGE := xipImage

diff --git a/arch/arm/include/asm/elf.h b/arch/arm/include/asm/elf.h
index 56211f2084ef871841215a0c4adfec6f778689d3..a8d036b482de5699a9f4e23593bf221a6510dfa6 100644 (file)
--- a/arch/arm/include/asm/elf.h
+++ b/arch/arm/include/asm/elf.h
@@ -50,6 +50,7 @@ typedef struct user_fp elf_fpregset_t;
 #define R_ARM_NONE             0
 #define R_ARM_PC24             1
 #define R_ARM_ABS32            2
+#define R_ARM_RELATIVE         23
 #define R_ARM_CALL             28
 #define R_ARM_JUMP24           29
 #define R_ARM_V4BX             40

diff --git a/arch/arm/kernel/.gitignore b/arch/arm/kernel/.gitignore
index c5f676c3c224b67afb51c50589e82fbf6d333c46..a055a4811aa801f3a0ee086e032aed37af143199 100644 (file)
--- a/arch/arm/kernel/.gitignore
+++ b/arch/arm/kernel/.gitignore
@@ -1 +1,2 @@
 vmlinux.lds
+pie.lds

diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
index dd9d90ab65d0cd7975031c0d67bf2cb8d1aefbb7..609536d9426632c9d1a610184fe598cad388445f 100644 (file)
--- a/arch/arm/kernel/Makefile
+++ b/arch/arm/kernel/Makefile
@@ -87,4 +87,6 @@ obj-y                         += psci.o
 obj-$(CONFIG_SMP)              += psci_smp.o
 endif
 
-extra-y := $(head-y) vmlinux.lds
+obj-$(CONFIG_PIE)              += pie.o
+
+extra-y := $(head-y) vmlinux.lds pie.lds

diff --git a/arch/arm/kernel/pie.c b/arch/arm/kernel/pie.c
new file mode 100644 (file)
index 0000000..5dff5d6
--- /dev/null
+++ b/arch/arm/kernel/pie.c
@@ -0,0 +1,83 @@
+/*
+ * Copyright 2013 Texas Instruments, Inc.
+ *     Russ Dill <russ.dill@ti.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/pie.h>
+#include <linux/elf.h>
+
+#include <asm/elf.h>
+
+extern char __pie_rel_dyn_start[];
+extern char __pie_rel_dyn_end[];
+extern char __pie_tail_offset[];
+
+struct arm_pie_tail {
+       int count;
+       uintptr_t offset[0];
+};
+
+int pie_arch_fill_tail(void *tail, void *common_start, void *common_end,
+                       void *overlay_start, void *code_start, void *code_end)
+{
+       Elf32_Rel *rel;
+       int records;
+       int i;
+       struct arm_pie_tail *pie_tail = tail;
+       int count;
+
+       rel = (Elf32_Rel *) __pie_rel_dyn_start;
+       records = (__pie_rel_dyn_end - __pie_rel_dyn_start) /
+                                               sizeof(*rel);
+
+       count = 0;
+       for (i = 0; i < records; i++, rel++) {
+               void *kern_off;
+               if (ELF32_R_TYPE(rel->r_info) != R_ARM_RELATIVE)
+                       return -ENOEXEC;
+
+               /* Adjust offset to match area in kernel */
+               kern_off = common_start + rel->r_offset;
+
+               if (kern_off >= common_start && kern_off < code_end) {
+                       if (tail)
+                               pie_tail->offset[count] = rel->r_offset;
+                       count++;
+               } else if (kern_off >= code_start && kern_off < code_end) {
+                       if (tail)
+                               pie_tail->offset[count] = rel->r_offset -
+                                               (code_start - overlay_start);
+                       count++;
+               }
+       }
+
+       if (tail)
+               pie_tail->count = count;
+
+       return count * sizeof(uintptr_t) + sizeof(*pie_tail);
+}
+EXPORT_SYMBOL_GPL(pie_arch_fill_tail);
+
+/*
+ * R_ARM_RELATIVE: B(S) + A
+ * B(S) - Addressing origin of the output segment defining the symbol S.
+ * A - Addend for the relocation.
+ */
+int pie_arch_fixup(struct pie_chunk *chunk, void *base, void *tail,
+                                               unsigned long offset)
+{
+       struct arm_pie_tail *pie_tail = tail;
+       int i;
+
+       /* Perform relocation fixups for given offset */
+       for (i = 0; i < pie_tail->count; i++)
+               *((uintptr_t *) (pie_tail->offset[i] + base)) += offset;
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(pie_arch_fixup);

diff --git a/arch/arm/kernel/pie.lds.S b/arch/arm/kernel/pie.lds.S
new file mode 100644 (file)
index 0000000..4fd5ac5
--- /dev/null
+++ b/arch/arm/kernel/pie.lds.S
@@ -0,0 +1,40 @@
+/*
+ * ld script to make ARM PIEs
+ * taken from the ARM vmlinux.lds.S version by Russ Dill <russ.dill@ti.com.
+ */
+
+#include <asm-generic/pie.lds.h>
+
+OUTPUT_ARCH(arm)
+
+SECTIONS
+{
+       . = 0x0;
+
+       PIE_COMMON_START
+       .got.plt : {
+               *(.got)
+               *(.got.plt)
+       }
+       .text : {
+               PIE_TEXT_TEXT
+       }
+       PIE_COMMON_END
+
+       PIE_OVERLAY_START
+       OVERLAY : NOCROSSREFS {
+       }
+       PIE_OVERLAY_SEND
+
+       __pie_rel_dyn_start : {
+               VMLINUX_SYMBOL(__pie_rel_dyn_start) = .;
+       }
+       .rel.dyn : {
+               KEEP(*(.rel*))
+       }
+       __pie_rel_dyn_end : {
+               VMLINUX_SYMBOL(__pie_rel_dyn_end) = .;
+       }
+
+       PIE_DISCARDS
+}

diff --git a/arch/arm/kernel/vmlinux.lds.S b/arch/arm/kernel/vmlinux.lds.S
index 33f2ea32f5a03602d5fc3c52d1b4d4e108a84ed6..fb1e0d78c285be0c948656b225effb4e376bbf83 100644 (file)
--- a/arch/arm/kernel/vmlinux.lds.S
+++ b/arch/arm/kernel/vmlinux.lds.S
@@ -81,6 +81,8 @@ SECTIONS
 #ifndef CONFIG_SMP_ON_UP
                *(.alt.smp.init)
 #endif
+               *(.pie.*)
+               *(.ARM.exidx.pie.*.text)
                *(.discard)
                *(.discard.*)
        }

diff --git a/arch/arm/libpie/.gitignore b/arch/arm/libpie/.gitignore
new file mode 100644 (file)
index 0000000..02e3cd5
--- /dev/null
+++ b/arch/arm/libpie/.gitignore
@@ -0,0 +1,3 @@
+lib1funcs.S
+ashldi3.S
+string.c

diff --git a/arch/arm/libpie/Makefile b/arch/arm/libpie/Makefile
new file mode 100644 (file)
index 0000000..5662e99
--- /dev/null
+++ b/arch/arm/libpie/Makefile
@@ -0,0 +1,32 @@
+#
+# linux/arch/arm/libpie/Makefile
+#
+ccflags-y      := -fpic -mno-single-pic-base -fno-builtin
+
+obj-y          := empty.o
+obj-y          += lib1funcs.o ashldi3.o string.o
+
+# string library code (-Os is enforced to keep it much smaller)
+string = $(obj)/string.o
+CFLAGS_string.o := -Os
+
+$(obj)/string.c: $(srctree)/arch/$(SRCARCH)/boot/compressed/string.c
+       $(call cmd,shipped)
+
+# For __aeabi_uidivmod
+lib1funcs = $(obj)/lib1funcs.o
+
+$(obj)/lib1funcs.S: $(srctree)/arch/$(SRCARCH)/lib/lib1funcs.S
+       $(call cmd,shipped)
+
+# For __aeabi_llsl
+ashldi3 = $(obj)/ashldi3.o
+
+$(obj)/ashldi3.S: $(srctree)/arch/$(SRCARCH)/lib/ashldi3.S
+       $(call cmd,shipped)
+
+$(obj)/libpie.o: $(string) $(lib1funcs) $(ashldi3) $(addprefix $(obj)/,$(OBJS))
+       $(call if_changed,ld)
+
+# Make sure files are removed during clean
+extra-y                += string.c lib1funcs.S ashldi3.S

diff --git a/arch/arm/libpie/empty.S b/arch/arm/libpie/empty.S
new file mode 100644 (file)
index 0000000..2416862
--- /dev/null
+++ b/arch/arm/libpie/empty.S
@@ -0,0 +1,12 @@
+#include <linux/linkage.h>
+
+ENTRY(__div0)
+ENTRY(__aeabi_unwind_cpp_pr0)
+ENTRY(__aeabi_unwind_cpp_pr1)
+ENTRY(__aeabi_unwind_cpp_pr2)
+       mov     pc, lr
+ENDPROC(__div0)
+ENDPROC(__aeabi_unwind_cpp_pr0)
+ENDPROC(__aeabi_unwind_cpp_pr1)
+ENDPROC(__aeabi_unwind_cpp_pr2)
+