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Message-ID: <51D398FE.7060700@cn.fujitsu.com>
Date: Wed, 03 Jul 2013 11:22:38 +0800
From: Zhang Yanfei <zhangyanfei@...fujitsu.com>
To: Kees Cook <keescook@...omium.org>
CC: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>,
"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
Yinghai Lu <yinghai@...nel.org>,
Matt Fleming <matt.fleming@...el.com>,
Borislav Petkov <bp@...en8.de>,
Alexander Duyck <alexander.h.duyck@...el.com>,
Jacob Shin <jacob.shin@....com>,
Pekka Enberg <penberg@...nel.org>
Subject: Re: [RESEND][PATCH] x86, relocs: move ELF relocation handling to
C
Hello Kees,
On 07/03/2013 02:22 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 support in support of KASLR.
>
> Based on work by Neill Clift and Michael Davidson.
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> 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 fe120da..f11ad6f 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
Here it still actually depends on x86_32, so why change the comment?
>
> 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
If you open this option for x86_64, the range should be modified a bit
to indicate the fact that on x86_64, the alignment of the kernel should
be at least 2M and the alignment itself should be 2M aligned.
otherwise, someone specifies an incorrect value here, say 0x300000,
which will cause the error:
#error "Invalid value for CONFIG_PHYSICAL_ALIGN"
when compiling the kernel.
> ---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))
I know you just moved the code. Could this macro be like this:
#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
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