Kaslr extended kernel text mapping region size from 512M to 1G, namely CONFIG_RANDOMIZE_BASE_MAX_OFFSET. This means kernel text can be mapped to below region:
[__START_KERNEL_map + LOAD_PHYSICAL_ADDR, __START_KERNEL_map + 1G] Introduce a function find_random_virt_offset() to get random value between LOAD_PHYSICAL_ADDR and CONFIG_RANDOMIZE_BASE_MAX_OFFSET. This random value will be added to __START_KERNEL_map to get the starting address which kernel text is mapped from. Since slot can be anywhere of this region, means it is a independent slot_area, it is easy to get a slot w.r.t random value. Signed-off-by: Baoquan He <[email protected]> --- arch/x86/boot/compressed/aslr.c | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c index 55adee2..332a8c4 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -383,6 +383,28 @@ static unsigned long find_random_phy_addr(unsigned long minimum, return slots_fetch_random(); } +static unsigned long find_random_virt_offset(unsigned long minimum, + unsigned long image_size) +{ + unsigned long slot_num, random; + struct mem_vector region, img; + + /* Make sure minimum is aligned. */ + minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN); + + if ( image_size <= CONFIG_PHYSICAL_ALIGN) + slot_num = ( CONFIG_RANDOMIZE_BASE_MAX_OFFSET - minimum ) / + CONFIG_PHYSICAL_ALIGN; + else + slot_num = ( CONFIG_RANDOMIZE_BASE_MAX_OFFSET - minimum - image_size ) / + CONFIG_PHYSICAL_ALIGN + 1; + + random = get_random_long() % slot_num; + + return random * CONFIG_PHYSICAL_ALIGN + minimum; +} + + static void add_kaslr_setup_data(struct boot_params *params, __u8 enabled) { struct setup_data *data; -- 1.9.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
