Messages in this thread Patch in this message | | | From | Baoquan He <> | Subject | [Patch v3 4/7] x86, kaslr: Introduce fetch_random_virt_offset to randomize the kernel text mapping address | Date | Sun, 8 Mar 2015 13:38:52 +0800 |
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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 an independent slot_area, it is simple to get a slot according to random value.
Signed-off-by: Baoquan He <bhe@redhat.com> --- 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 afb1641..0ca4c5b 100644 --- a/arch/x86/boot/compressed/aslr.c +++ b/arch/x86/boot/compressed/aslr.c @@ -382,6 +382,28 @@ static unsigned long find_random_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; + + /* 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
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