[PATCH v2] x86, relocs: move ELF relocation handling to C

[PATCH v2] x86, relocs: move ELF relocation handling to C

[Kees Cook]

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>
---
v2:
 - several suggestions from Zhang Yanfei:
   - adjusted Kconfig ranges to be per-architecture, updated help text.
   - used ALIGN macro
---
 arch/x86/Kconfig                     |    8 +++-
 arch/x86/Makefile                    |    8 ++--
 arch/x86/boot/compressed/head_32.S   |   31 ++------------
 arch/x86/boot/compressed/head_64.S   |    1 +
 arch/x86/boot/compressed/misc.c      |   77 +++++++++++++++++++++++++++++++++-
 arch/x86/include/asm/page_32_types.h |    2 +
 arch/x86/include/asm/page_64_types.h |    5 ---
 arch/x86/include/asm/page_types.h    |    5 +++
 8 files changed, 97 insertions(+), 40 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 265c672..7598b55 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1715,9 +1715,10 @@ 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
@@ -1735,6 +1736,9 @@ 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
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 07639c6..41250fb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 1e3184f..5d6f689 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -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.
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 06e71c2..c337422 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -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
 
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 7cb56c6..b756a04 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -267,6 +267,79 @@ 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
@@ -321,7 +394,8 @@ 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;
 
@@ -361,6 +435,7 @@ 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;
 }
diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index ef17af0..f48b17d 100644
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -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)
 
diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6c896fb..43dcd80 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -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. */
diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
index 54c9787..f97fbe3 100644
--- a/arch/x86/include/asm/page_types.h
+++ b/arch/x86/include/asm/page_types.h
@@ -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
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security

Re: [PATCH v2] x86, relocs: move ELF relocation handling to C

[Zhang Yanfei]

On 07/09/2013 12:15 AM, Kees Cook wrote:
> 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>

Acked-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

> ---
> v2:
>  - several suggestions from Zhang Yanfei:
>    - adjusted Kconfig ranges to be per-architecture, updated help text.
>    - used ALIGN macro
> ---
>  arch/x86/Kconfig                     |    8 +++-
>  arch/x86/Makefile                    |    8 ++--
>  arch/x86/boot/compressed/head_32.S   |   31 ++------------
>  arch/x86/boot/compressed/head_64.S   |    1 +
>  arch/x86/boot/compressed/misc.c      |   77 +++++++++++++++++++++++++++++++++-
>  arch/x86/include/asm/page_32_types.h |    2 +
>  arch/x86/include/asm/page_64_types.h |    5 ---
>  arch/x86/include/asm/page_types.h    |    5 +++
>  8 files changed, 97 insertions(+), 40 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 265c672..7598b55 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1715,9 +1715,10 @@ 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
> @@ -1735,6 +1736,9 @@ 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
> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
> index 07639c6..41250fb 100644
> --- a/arch/x86/Makefile
> +++ b/arch/x86/Makefile
> @@ -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
> diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
> index 1e3184f..5d6f689 100644
> --- a/arch/x86/boot/compressed/head_32.S
> +++ b/arch/x86/boot/compressed/head_32.S
> @@ -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.
> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> index 06e71c2..c337422 100644
> --- a/arch/x86/boot/compressed/head_64.S
> +++ b/arch/x86/boot/compressed/head_64.S
> @@ -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
>  
> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
> index 7cb56c6..b756a04 100644
> --- a/arch/x86/boot/compressed/misc.c
> +++ b/arch/x86/boot/compressed/misc.c
> @@ -267,6 +267,79 @@ 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
> @@ -321,7 +394,8 @@ 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;
>  
> @@ -361,6 +435,7 @@ 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;
>  }
> diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
> index ef17af0..f48b17d 100644
> --- a/arch/x86/include/asm/page_32_types.h
> +++ b/arch/x86/include/asm/page_32_types.h
> @@ -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)
>  
> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
> index 6c896fb..43dcd80 100644
> --- a/arch/x86/include/asm/page_64_types.h
> +++ b/arch/x86/include/asm/page_64_types.h
> @@ -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. */
> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
> index 54c9787..f97fbe3 100644
> --- a/arch/x86/include/asm/page_types.h
> +++ b/arch/x86/include/asm/page_types.h
> @@ -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


-- 
Thanks.
Zhang Yanfei

Re: [PATCH v2] x86, relocs: move ELF relocation handling to C

[Kees Cook]

On Mon, Jul 8, 2013 at 10:35 AM, Zhang Yanfei <zhangyanfei.yes@gmail.com> wrote:
> On 07/09/2013 12:15 AM, Kees Cook wrote:
>> 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>
>
> Acked-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>

Hi Peter,

Can this get added to tip?

Thanks,

-Kees

>
>> ---
>> v2:
>>  - several suggestions from Zhang Yanfei:
>>    - adjusted Kconfig ranges to be per-architecture, updated help text.
>>    - used ALIGN macro
>> ---
>>  arch/x86/Kconfig                     |    8 +++-
>>  arch/x86/Makefile                    |    8 ++--
>>  arch/x86/boot/compressed/head_32.S   |   31 ++------------
>>  arch/x86/boot/compressed/head_64.S   |    1 +
>>  arch/x86/boot/compressed/misc.c      |   77 +++++++++++++++++++++++++++++++++-
>>  arch/x86/include/asm/page_32_types.h |    2 +
>>  arch/x86/include/asm/page_64_types.h |    5 ---
>>  arch/x86/include/asm/page_types.h    |    5 +++
>>  8 files changed, 97 insertions(+), 40 deletions(-)
>>
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 265c672..7598b55 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1715,9 +1715,10 @@ 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
>> @@ -1735,6 +1736,9 @@ 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
>> diff --git a/arch/x86/Makefile b/arch/x86/Makefile
>> index 07639c6..41250fb 100644
>> --- a/arch/x86/Makefile
>> +++ b/arch/x86/Makefile
>> @@ -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
>> diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
>> index 1e3184f..5d6f689 100644
>> --- a/arch/x86/boot/compressed/head_32.S
>> +++ b/arch/x86/boot/compressed/head_32.S
>> @@ -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.
>> diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
>> index 06e71c2..c337422 100644
>> --- a/arch/x86/boot/compressed/head_64.S
>> +++ b/arch/x86/boot/compressed/head_64.S
>> @@ -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
>>
>> diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
>> index 7cb56c6..b756a04 100644
>> --- a/arch/x86/boot/compressed/misc.c
>> +++ b/arch/x86/boot/compressed/misc.c
>> @@ -267,6 +267,79 @@ 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
>> @@ -321,7 +394,8 @@ 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;
>>
>> @@ -361,6 +435,7 @@ 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;
>>  }
>> diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
>> index ef17af0..f48b17d 100644
>> --- a/arch/x86/include/asm/page_32_types.h
>> +++ b/arch/x86/include/asm/page_32_types.h
>> @@ -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)
>>
>> diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
>> index 6c896fb..43dcd80 100644
>> --- a/arch/x86/include/asm/page_64_types.h
>> +++ b/arch/x86/include/asm/page_64_types.h
>> @@ -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. */
>> diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
>> index 54c9787..f97fbe3 100644
>> --- a/arch/x86/include/asm/page_types.h
>> +++ b/arch/x86/include/asm/page_types.h
>> @@ -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
>
>
> --
> Thanks.
> Zhang Yanfei



-- 
Kees Cook
Chrome OS Security

Re: [PATCH v2] x86, relocs: move ELF relocation handling to C

[H. Peter Anvin]

On 08/07/2013 06:34 PM, Kees Cook wrote:
> 
> Hi Peter,
> 
> Can this get added to tip?
> 
> Thanks,
> 
> -Kees
> 

Sorry, missed the 7/8 update...

	-hpa

[tip:x86/kaslr] x86, relocs: Move ELF relocation handling to C

[tip-bot for Kees Cook]

Commit-ID:  a02150610776f66b40257624822a879311592bb2
Gitweb:     http://git.kernel.org/tip/a02150610776f66b40257624822a879311592bb2
Author:     Kees Cook <keescook@chromium.org>
AuthorDate: Mon, 8 Jul 2013 09:15:17 -0700
Committer:  H. Peter Anvin <hpa@linux.intel.com>
CommitDate: Wed, 7 Aug 2013 21:00:04 -0700

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>
---
 arch/x86/Kconfig                     |  8 +++-
 arch/x86/Makefile                    |  8 ++--
 arch/x86/boot/compressed/head_32.S   | 31 ++-------------
 arch/x86/boot/compressed/head_64.S   |  1 +
 arch/x86/boot/compressed/misc.c      | 77 +++++++++++++++++++++++++++++++++++-
 arch/x86/include/asm/page_32_types.h |  2 +
 arch/x86/include/asm/page_64_types.h |  5 ---
 arch/x86/include/asm/page_types.h    |  5 +++
 8 files changed, 97 insertions(+), 40 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b32ebf9..8002668 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -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
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 07639c6..41250fb 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 1e3184f..5d6f689 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -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.
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 06e71c2..c337422 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -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
 
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 0319c88..434f077 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -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;
 }
diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index ef17af0..f48b17d 100644
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -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)
 
diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6c896fb..43dcd80 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -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. */
diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
index 54c9787..f97fbe3 100644
--- a/arch/x86/include/asm/page_types.h
+++ b/arch/x86/include/asm/page_types.h
@@ -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

[PATCH v2] x86, relocs: move ELF relocation handling to C

[Kees Cook]

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 support in support of KASLR.

Based on work by Neill Clift and Michael Davidson.

Signed-off-by: Kees Cook <keescook@chromium.org>
---
v2:
 - clarified commit message.
---
 arch/x86/Kconfig                     |    4 +-
 arch/x86/Makefile                    |    8 ++--
 arch/x86/boot/compressed/head_32.S   |   31 ++------------
 arch/x86/boot/compressed/head_64.S   |    1 +
 arch/x86/boot/compressed/misc.c      |   77 +++++++++++++++++++++++++++++++++-
 arch/x86/include/asm/page_32_types.h |    2 +
 arch/x86/include/asm/page_64_types.h |    5 ---
 arch/x86/include/asm/page_types.h    |    6 +++
 8 files changed, 94 insertions(+), 40 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 685692c..b4797b9 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1695,13 +1695,13 @@ config RELOCATABLE
 	  it has been loaded at and the compile time physical address
 	  (CONFIG_PHYSICAL_START) is ignored.
 
-# Relocation on x86-32 needs some additional build support
+# Relocation on x86 needs some additional build support
 config X86_NEED_RELOCS
 	def_bool y
 	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
 	---help---
diff --git a/arch/x86/Makefile b/arch/x86/Makefile
index 5c47726..43f8cef 100644
--- a/arch/x86/Makefile
+++ b/arch/x86/Makefile
@@ -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
diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S
index 1e3184f..5d6f689 100644
--- a/arch/x86/boot/compressed/head_32.S
+++ b/arch/x86/boot/compressed/head_32.S
@@ -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.
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 16f24e6..6632693 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -340,6 +340,7 @@ 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
 
diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c
index 7cb56c6..b756a04 100644
--- a/arch/x86/boot/compressed/misc.c
+++ b/arch/x86/boot/compressed/misc.c
@@ -267,6 +267,79 @@ 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
@@ -321,7 +394,8 @@ 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;
 
@@ -361,6 +435,7 @@ 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;
 }
diff --git a/arch/x86/include/asm/page_32_types.h b/arch/x86/include/asm/page_32_types.h
index ef17af0..f48b17d 100644
--- a/arch/x86/include/asm/page_32_types.h
+++ b/arch/x86/include/asm/page_32_types.h
@@ -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)
 
diff --git a/arch/x86/include/asm/page_64_types.h b/arch/x86/include/asm/page_64_types.h
index 6c896fb..43dcd80 100644
--- a/arch/x86/include/asm/page_64_types.h
+++ b/arch/x86/include/asm/page_64_types.h
@@ -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. */
diff --git a/arch/x86/include/asm/page_types.h b/arch/x86/include/asm/page_types.h
index 54c9787..086c2fa 100644
--- a/arch/x86/include/asm/page_types.h
+++ b/arch/x86/include/asm/page_types.h
@@ -33,6 +33,12 @@
 	(((current->personality & READ_IMPLIES_EXEC) ? VM_EXEC : 0 ) | \
 	 VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC)
 
+#define __PHYSICAL_START	((CONFIG_PHYSICAL_START +		\
+				  (CONFIG_PHYSICAL_ALIGN - 1)) &	\
+				 ~(CONFIG_PHYSICAL_ALIGN - 1))
+
+#define __START_KERNEL		(__START_KERNEL_map + __PHYSICAL_START)
+
 #ifdef CONFIG_X86_64
 #include <asm/page_64_types.h>
 #else
-- 
1.7.9.5


-- 
Kees Cook
Chrome OS Security