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 very simple to get a slot according to random value.
Signed-off-by: Baoquan He <b...@redhat.com>
---
arch/x86/boot/compressed/aslr.c | 21 +++++++++++++++++++++
1 file changed, 21 insertions(+)
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index fa6192b..3730a33 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -366,6 +366,27 @@ 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;
+}
+
unsigned char *choose_kernel_location(unsigned char *input,
unsigned long input_size,
unsigned char *output,
--
2.5.0
