lkml.org 
[lkml]   [2015]   [Mar]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH v2 8/9] introduce fetch_random_virt_offset to randomize the kernel text mapping address
Date
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 <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 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


\
 
 \ /
  Last update: 2015-03-02 16:21    [W:0.268 / U:1.024 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site