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x86, relocs: Move ELF relocation handling to C 

Moves the relocation handling into C, after decompression. This requires
that the decompressed size is passed to the decompression routine as
well so that relocations can be found. Only kernels that need relocation
support will use the code (currently just x86_32), but this is laying
the ground work for 64-bit using it in support of KASLR.

Based on work by Neill Clift and Michael Davidson.

Signed-off-by: Kees Cook <keescook@chromium.org>
Link: http://lkml.kernel.org/r/20130708161517.GA4832@www.outflux.net
Acked-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
This commit is contained in:
Kees Cook 2013-07-08 09:15:17 -07:00 committed by H. Peter Anvin
parent c095ba7224
commit a021506107
8 changed files with 97 additions and 40 deletions
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8
arch/x86/Kconfig
View File

@ -1716,9 +1716,10 @@ config X86_NEED_RELOCS
depends on X86_32 && RELOCATABLE
config PHYSICAL_ALIGN
hex "Alignment value to which kernel should be aligned" if X86_32
hex "Alignment value to which kernel should be aligned"
default "0x1000000"
range 0x2000 0x1000000
range 0x2000 0x1000000 if X86_32
range 0x200000 0x1000000 if X86_64
---help---
This value puts the alignment restrictions on physical address
where kernel is loaded and run from. Kernel is compiled for an
@ -1736,6 +1737,9 @@ config PHYSICAL_ALIGN
end result is that kernel runs from a physical address meeting
above alignment restrictions.
On 32-bit this value must be a multiple of 0x2000. On 64-bit
this value must be a multiple of 0x200000.
Don't change this unless you know what you are doing.
config HOTPLUG_CPU

8
arch/x86/Makefile
View File

@ -16,6 +16,10 @@ endif
# e.g.: obj-y += foo_$(BITS).o
export BITS
ifdef CONFIG_X86_NEED_RELOCS
LDFLAGS_vmlinux := --emit-relocs
endif
ifeq ($(CONFIG_X86_32),y)
BITS := 32
UTS_MACHINE := i386
@ -25,10 +29,6 @@ ifeq ($(CONFIG_X86_32),y)
KBUILD_AFLAGS += $(biarch)
KBUILD_CFLAGS += $(biarch)
ifdef CONFIG_RELOCATABLE
LDFLAGS_vmlinux := --emit-relocs
endif
KBUILD_CFLAGS += -msoft-float -mregparm=3 -freg-struct-return
# Never want PIC in a 32-bit kernel, prevent breakage with GCC built

31
arch/x86/boot/compressed/head_32.S
View File

@ -181,8 +181,9 @@ relocated:
/*
* Do the decompression, and jump to the new kernel..
*/
leal z_extract_offset_negative(%ebx), %ebp
/* push arguments for decompress_kernel: */
pushl $z_output_len /* decompressed length */
leal z_extract_offset_negative(%ebx), %ebp
pushl %ebp /* output address */
pushl $z_input_len /* input_len */
leal input_data(%ebx), %eax
@ -191,33 +192,7 @@ relocated:
pushl %eax /* heap area */
pushl %esi /* real mode pointer */
call decompress_kernel
addl $20, %esp
#if CONFIG_RELOCATABLE
/*
* Find the address of the relocations.
*/
leal z_output_len(%ebp), %edi
/*
* Calculate the delta between where vmlinux was compiled to run
* and where it was actually loaded.
*/
movl %ebp, %ebx
subl $LOAD_PHYSICAL_ADDR, %ebx
jz 2f /* Nothing to be done if loaded at compiled addr. */
/*
* Process relocations.
*/
1: subl $4, %edi
movl (%edi), %ecx
testl %ecx, %ecx
jz 2f
addl %ebx, -__PAGE_OFFSET(%ebx, %ecx)
jmp 1b
2:
#endif
addl $24, %esp
/*
* Jump to the decompressed kernel.

1
arch/x86/boot/compressed/head_64.S
View File

@ -338,6 +338,7 @@ relocated:
leaq input_data(%rip), %rdx /* input_data */
movl $z_input_len, %ecx /* input_len */
movq %rbp, %r8 /* output target address */
movq $z_output_len, %r9 /* decompressed length */
call decompress_kernel
popq %rsi

77
arch/x86/boot/compressed/misc.c
View File

@ -271,6 +271,79 @@ static void error(char *x)
asm("hlt");
}
#if CONFIG_X86_NEED_RELOCS
static void handle_relocations(void *output, unsigned long output_len)
{
int *reloc;
unsigned long delta, map, ptr;
unsigned long min_addr = (unsigned long)output;
unsigned long max_addr = min_addr + output_len;
/*
* Calculate the delta between where vmlinux was linked to load
* and where it was actually loaded.
*/
delta = min_addr - LOAD_PHYSICAL_ADDR;
if (!delta) {
debug_putstr("No relocation needed... ");
return;
}
debug_putstr("Performing relocations... ");
/*
* The kernel contains a table of relocation addresses. Those
* addresses have the final load address of the kernel in virtual
* memory. We are currently working in the self map. So we need to
* create an adjustment for kernel memory addresses to the self map.
* This will involve subtracting out the base address of the kernel.
*/
map = delta - __START_KERNEL_map;
/*
* Process relocations: 32 bit relocations first then 64 bit after.
* Two sets of binary relocations are added to the end of the kernel
* before compression. Each relocation table entry is the kernel
* address of the location which needs to be updated stored as a
* 32-bit value which is sign extended to 64 bits.
*
* Format is:
*
* kernel bits...
* 0 - zero terminator for 64 bit relocations
* 64 bit relocation repeated
* 0 - zero terminator for 32 bit relocations
* 32 bit relocation repeated
*
* So we work backwards from the end of the decompressed image.
*/
for (reloc = output + output_len - sizeof(*reloc); *reloc; reloc--) {
int extended = *reloc;
extended += map;
ptr = (unsigned long)extended;
if (ptr < min_addr || ptr > max_addr)
error("32-bit relocation outside of kernel!\n");
*(uint32_t *)ptr += delta;
}
#ifdef CONFIG_X86_64
for (reloc--; *reloc; reloc--) {
long extended = *reloc;
extended += map;
ptr = (unsigned long)extended;
if (ptr < min_addr || ptr > max_addr)
error("64-bit relocation outside of kernel!\n");
*(uint64_t *)ptr += delta;
}
#endif
}
#else
static inline void handle_relocations(void *output, unsigned long output_len)
{ }
#endif
static void parse_elf(void *output)
{
#ifdef CONFIG_X86_64
@ -325,7 +398,8 @@ static void parse_elf(void *output)
asmlinkage void decompress_kernel(void *rmode, memptr heap,
unsigned char *input_data,
unsigned long input_len,
unsigned char *output)
unsigned char *output,
unsigned long output_len)
{
real_mode = rmode;
@ -365,6 +439,7 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap,
debug_putstr("\nDecompressing Linux... ");
decompress(input_data, input_len, NULL, NULL, output, NULL, error);
parse_elf(output);
handle_relocations(output, output_len);
debug_putstr("done.\nBooting the kernel.\n");
return;
}

2
arch/x86/include/asm/page_32_types.h
View File

@ -15,6 +15,8 @@
*/
#define __PAGE_OFFSET _AC(CONFIG_PAGE_OFFSET, UL)
#define __START_KERNEL_map __PAGE_OFFSET
#define THREAD_SIZE_ORDER 1
#define THREAD_SIZE (PAGE_SIZE << THREAD_SIZE_ORDER)

5
arch/x86/include/asm/page_64_types.h
View File

@ -32,11 +32,6 @@
*/
#define __PAGE_OFFSET _AC(0xffff880000000000, UL)
#define __PHYSICAL_START ((CONFIG_PHYSICAL_START + \
(CONFIG_PHYSICAL_ALIGN - 1)) & \
~(CONFIG_PHYSICAL_ALIGN - 1))
#define __START_KERNEL (__START_KERNEL_map + __PHYSICAL_START)
#define __START_KERNEL_map _AC(0xffffffff80000000, UL)
/* See Documentation/x86/x86_64/mm.txt for a description of the memory map. */

5
arch/x86/include/asm/page_types.h
View File

@ -33,6 +33,11 @@
(((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \
VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
#define __PHYSICAL_START ALIGN(CONFIG_PHYSICAL_START, \
CONFIG_PHYSICAL_ALIGN)
#define __START_KERNEL (__START_KERNEL_map + __PHYSICAL_START)
#ifdef CONFIG_X86_64
#include <asm/page_64_types.h>
#else