From a02150610776f66b40257624822a879311592bb2 Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Mon, 8 Jul 2013 09:15:17 -0700 Subject: [PATCH] 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 Link: http://lkml.kernel.org/r/20130708161517.GA4832@www.outflux.net Acked-by: Zhang Yanfei Signed-off-by: H. Peter Anvin --- 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 b32ebf92b0ce..8002668d60a1 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 07639c656fcd..41250fb33985 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 1e3184f6072f..5d6f6891b188 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 06e71c2c16bf..c337422b575d 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 0319c88290a5..434f077d2c4d 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 ef17af013475..f48b17df4224 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 6c896fbe21db..43dcd804ebd5 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 54c97879195e..f97fbe3abb67 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 #else