From 8ab3820fd5b2896d66da7bb2a906bc382e63e7bc Mon Sep 17 00:00:00 2001 From: Kees Cook Date: Thu, 10 Oct 2013 17:18:14 -0700 Subject: [PATCH] x86, kaslr: Return location from decompress_kernel This allows decompress_kernel to return a new location for the kernel to be relocated to. Additionally, enforces CONFIG_PHYSICAL_START as the minimum relocation position when building with CONFIG_RELOCATABLE. With CONFIG_RANDOMIZE_BASE set, the choose_kernel_location routine will select a new location to decompress the kernel, though here it is presently a no-op. The kernel command line option "nokaslr" is introduced to bypass these routines. Signed-off-by: Kees Cook Link: http://lkml.kernel.org/r/1381450698-28710-3-git-send-email-keescook@chromium.org Signed-off-by: H. Peter Anvin --- Documentation/kernel-parameters.txt | 4 +++ arch/x86/Kconfig | 38 ++++++++++++++++++++++++++--- arch/x86/boot/compressed/Makefile | 2 +- arch/x86/boot/compressed/aslr.c | 23 +++++++++++++++++ arch/x86/boot/compressed/cmdline.c | 2 +- arch/x86/boot/compressed/head_32.S | 10 +++++--- arch/x86/boot/compressed/head_64.S | 16 +++++++----- arch/x86/boot/compressed/misc.c | 8 ++++-- arch/x86/boot/compressed/misc.h | 27 +++++++++++++++----- 9 files changed, 106 insertions(+), 24 deletions(-) create mode 100644 arch/x86/boot/compressed/aslr.c diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index fcbb736d55fe..773fc4c077b4 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1975,6 +1975,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted. noapic [SMP,APIC] Tells the kernel to not make use of any IOAPICs that may be present in the system. + nokaslr [X86] + Disable kernel base offset ASLR (Address Space + Layout Randomization) if built into the kernel. + noautogroup Disable scheduler automatic task group creation. nobats [PPC] Do not use BATs for mapping kernel lowmem diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index ee2fb9d37745..992701d4d4f8 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -1722,16 +1722,46 @@ config RELOCATABLE Note: If CONFIG_RELOCATABLE=y, then the kernel runs from the address it has been loaded at and the compile time physical address - (CONFIG_PHYSICAL_START) is ignored. + (CONFIG_PHYSICAL_START) is used as the minimum location. -# Relocation on x86-32 needs some additional build support +config RANDOMIZE_BASE + bool "Randomize the address of the kernel image" + depends on RELOCATABLE + depends on !HIBERNATION + default n + ---help--- + Randomizes the physical and virtual address at which the + kernel image is decompressed, as a security feature that + deters exploit attempts relying on knowledge of the location + of kernel internals. + + Entropy is generated using the RDRAND instruction if it + is supported. If not, then RDTSC is used, if supported. If + neither RDRAND nor RDTSC are supported, then no randomness + is introduced. + + The kernel will be offset by up to RANDOMIZE_BASE_MAX_OFFSET, + and aligned according to PHYSICAL_ALIGN. + +config RANDOMIZE_BASE_MAX_OFFSET + hex "Maximum ASLR offset allowed" + depends on RANDOMIZE_BASE + default "0x10000000" + range 0x0 0x10000000 + ---help--- + Determines the maximal offset in bytes that will be applied to the + kernel when Address Space Layout Randomization (ASLR) is active. + Must be less than or equal to the actual physical memory on the + system. This must be a power of two. + +# Relocation on x86 needs some additional build support config X86_NEED_RELOCS def_bool y - depends on X86_32 && RELOCATABLE + depends on RANDOMIZE_BASE || (X86_32 && RELOCATABLE) config PHYSICAL_ALIGN hex "Alignment value to which kernel should be aligned" - default "0x1000000" + default "0x200000" range 0x2000 0x1000000 if X86_32 range 0x200000 0x1000000 if X86_64 ---help--- diff --git a/arch/x86/boot/compressed/Makefile b/arch/x86/boot/compressed/Makefile index 3312f1be9fd9..ae8b5dbbd8c5 100644 --- a/arch/x86/boot/compressed/Makefile +++ b/arch/x86/boot/compressed/Makefile @@ -27,7 +27,7 @@ HOST_EXTRACFLAGS += -I$(srctree)/tools/include VMLINUX_OBJS = $(obj)/vmlinux.lds $(obj)/head_$(BITS).o $(obj)/misc.o \ $(obj)/string.o $(obj)/cmdline.o $(obj)/early_serial_console.o \ - $(obj)/piggy.o $(obj)/cpuflags.o + $(obj)/piggy.o $(obj)/cpuflags.o $(obj)/aslr.o $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c new file mode 100644 index 000000000000..b73cc66d201e --- /dev/null +++ b/arch/x86/boot/compressed/aslr.c @@ -0,0 +1,23 @@ +#include "misc.h" + +#ifdef CONFIG_RANDOMIZE_BASE + +unsigned char *choose_kernel_location(unsigned char *input, + unsigned long input_size, + unsigned char *output, + unsigned long output_size) +{ + unsigned long choice = (unsigned long)output; + + if (cmdline_find_option_bool("nokaslr")) { + debug_putstr("KASLR disabled...\n"); + goto out; + } + + /* XXX: choose random location. */ + +out: + return (unsigned char *)choice; +} + +#endif /* CONFIG_RANDOMIZE_BASE */ diff --git a/arch/x86/boot/compressed/cmdline.c b/arch/x86/boot/compressed/cmdline.c index bffd73b45b1f..b68e3033e6b9 100644 --- a/arch/x86/boot/compressed/cmdline.c +++ b/arch/x86/boot/compressed/cmdline.c @@ -1,6 +1,6 @@ #include "misc.h" -#ifdef CONFIG_EARLY_PRINTK +#if CONFIG_EARLY_PRINTK || CONFIG_RANDOMIZE_BASE static unsigned long fs; static inline void set_fs(unsigned long seg) diff --git a/arch/x86/boot/compressed/head_32.S b/arch/x86/boot/compressed/head_32.S index 5d6f6891b188..9116aac232c7 100644 --- a/arch/x86/boot/compressed/head_32.S +++ b/arch/x86/boot/compressed/head_32.S @@ -117,9 +117,11 @@ preferred_addr: addl %eax, %ebx notl %eax andl %eax, %ebx -#else - movl $LOAD_PHYSICAL_ADDR, %ebx + cmpl $LOAD_PHYSICAL_ADDR, %ebx + jge 1f #endif + movl $LOAD_PHYSICAL_ADDR, %ebx +1: /* Target address to relocate to for decompression */ addl $z_extract_offset, %ebx @@ -191,14 +193,14 @@ relocated: leal boot_heap(%ebx), %eax pushl %eax /* heap area */ pushl %esi /* real mode pointer */ - call decompress_kernel + call decompress_kernel /* returns kernel location in %eax */ addl $24, %esp /* * Jump to the decompressed kernel. */ xorl %ebx, %ebx - jmp *%ebp + jmp *%eax /* * Stack and heap for uncompression diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index c337422b575d..c5c1ae0997e7 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -94,9 +94,11 @@ ENTRY(startup_32) addl %eax, %ebx notl %eax andl %eax, %ebx -#else - movl $LOAD_PHYSICAL_ADDR, %ebx + cmpl $LOAD_PHYSICAL_ADDR, %ebx + jge 1f #endif + movl $LOAD_PHYSICAL_ADDR, %ebx +1: /* Target address to relocate to for decompression */ addl $z_extract_offset, %ebx @@ -269,9 +271,11 @@ preferred_addr: addq %rax, %rbp notq %rax andq %rax, %rbp -#else - movq $LOAD_PHYSICAL_ADDR, %rbp + cmpq $LOAD_PHYSICAL_ADDR, %rbp + jge 1f #endif + movq $LOAD_PHYSICAL_ADDR, %rbp +1: /* Target address to relocate to for decompression */ leaq z_extract_offset(%rbp), %rbx @@ -339,13 +343,13 @@ relocated: movl $z_input_len, %ecx /* input_len */ movq %rbp, %r8 /* output target address */ movq $z_output_len, %r9 /* decompressed length */ - call decompress_kernel + call decompress_kernel /* returns kernel location in %rax */ popq %rsi /* * Jump to the decompressed kernel. */ - jmp *%rbp + jmp *%rax .code32 no_longmode: diff --git a/arch/x86/boot/compressed/misc.c b/arch/x86/boot/compressed/misc.c index 434f077d2c4d..71387685dc16 100644 --- a/arch/x86/boot/compressed/misc.c +++ b/arch/x86/boot/compressed/misc.c @@ -395,7 +395,7 @@ static void parse_elf(void *output) free(phdrs); } -asmlinkage void decompress_kernel(void *rmode, memptr heap, +asmlinkage void *decompress_kernel(void *rmode, memptr heap, unsigned char *input_data, unsigned long input_len, unsigned char *output, @@ -422,6 +422,10 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap, free_mem_ptr = heap; /* Heap */ free_mem_end_ptr = heap + BOOT_HEAP_SIZE; + output = choose_kernel_location(input_data, input_len, + output, output_len); + + /* Validate memory location choices. */ if ((unsigned long)output & (MIN_KERNEL_ALIGN - 1)) error("Destination address inappropriately aligned"); #ifdef CONFIG_X86_64 @@ -441,5 +445,5 @@ asmlinkage void decompress_kernel(void *rmode, memptr heap, parse_elf(output); handle_relocations(output, output_len); debug_putstr("done.\nBooting the kernel.\n"); - return; + return output; } diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h index 674019d8e235..9077af7fd0b8 100644 --- a/arch/x86/boot/compressed/misc.h +++ b/arch/x86/boot/compressed/misc.h @@ -39,23 +39,38 @@ static inline void debug_putstr(const char *s) #endif -#ifdef CONFIG_EARLY_PRINTK - +#if CONFIG_EARLY_PRINTK || CONFIG_RANDOMIZE_BASE /* cmdline.c */ int cmdline_find_option(const char *option, char *buffer, int bufsize); int cmdline_find_option_bool(const char *option); +#endif -/* early_serial_console.c */ -extern int early_serial_base; -void console_init(void); +#if CONFIG_RANDOMIZE_BASE +/* aslr.c */ +unsigned char *choose_kernel_location(unsigned char *input, + unsigned long input_size, + unsigned char *output, + unsigned long output_size); #else +static inline +unsigned char *choose_kernel_location(unsigned char *input, + unsigned long input_size, + unsigned char *output, + unsigned long output_size) +{ + return output; +} +#endif +#ifdef CONFIG_EARLY_PRINTK /* early_serial_console.c */ +extern int early_serial_base; +void console_init(void); +#else static const int early_serial_base; static inline void console_init(void) { } - #endif #endif -- GitLab