Messages in this thread Patch in this message | | | From | Kees Cook <> | Subject | [PATCH 5/6] x86: kaslr: select memory region from e820 maps | Date | Thu, 25 Apr 2013 14:54:19 -0700 |
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This chooses the largest contiguous RAM region for the KASLR offset to live in.
Signed-off-by: Kees Cook <keescook@chromium.org> --- arch/x86/boot/compressed/aslr.c | 43 +++++++++++++++++++++++++++++++++------ 1 file changed, 37 insertions(+), 6 deletions(-)
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index 11a91c6..8f21ebe 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -1,6 +1,7 @@ #include "misc.h" #ifdef CONFIG_RANDOMIZE_BASE +#include <asm/e820.h> #include <asm/archrandom.h> static inline int rdrand(unsigned long *v) @@ -56,28 +57,58 @@ static unsigned long get_random_long(void) return 0; } +int largest_ram_region(unsigned long *start, unsigned long *size) +{ + int i, rc = 0; + + *size = 0; + for (i = 0; i < real_mode->e820_entries; i++) { + struct e820entry *entry = &real_mode->e820_map[i]; + + if (entry->type != E820_RAM) + continue; + + if (entry->size > *size) { + *size = entry->size; + *start = entry->addr; + rc = 1; + } + } + return rc; +} + unsigned char *choose_kernel_location(unsigned char *hint, unsigned long size) { unsigned char *choice = hint; unsigned long random, mask; + unsigned long addr, length; if (cmdline_find_option_bool("noaslr")) { debug_putstr("KASLR disabled...\n"); goto out; } + /* Find an appropriate E820 entry. */ + if (!largest_ram_region(&addr, &length)) { + debug_putstr("KASLR could not find suitable E820 region...\n"); + goto out; + } + random = get_random_long(); - /* Clip off top of the range. */ + /* XXX: Rework page tables to handle arbitrary physical location. */ mask = CONFIG_RANDOMIZE_BASE_MAX_OFFSET - 1; random &= mask; - /* XXX: Find an appropriate E820 hole, instead of adding hint. */ - random += (unsigned long)hint; + /* Clip to E820 entry size. */ + while (random > length) + random >>= 1; + + /* Offset the target. */ + random += addr; - /* XXX: Clip to E820 hole, instead of just using hint. */ - mask = (unsigned long)hint + CONFIG_RANDOMIZE_BASE_MAX_OFFSET; - while (random + size > mask) + /* Clip end to E820 entry size. */ + while (random + size > addr + length) random >>= 1; /* Clip off bottom of range (via alignment). */ -- 1.7.9.5
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