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x86/KASLR: Add virtual address choosing function

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To support randomizing the kernel virtual address separately from the
physical address, this patch adds find_random_virt_addr() to choose
a slot anywhere between LOAD_PHYSICAL_ADDR and KERNEL_IMAGE_SIZE.
Since this address is virtual, not physical, we can place the kernel
anywhere in this region, as long as it is aligned and (in the case of
kernel being larger than the slot size) placed with enough room to load
the entire kernel image.

For clarity and readability, find_random_addr() is renamed to
find_random_phys_addr() and has "size" renamed to "image_size" to match
find_random_virt_addr().

Signed-off-by: Baoquan He <bhe@redhat.com>
[ Rewrote changelog, refactored slot calculation for readability. ]
[ Renamed find_random_phys_addr() and size argument. ]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Yinghai Lu <yinghai@kernel.org>
Cc: kernel-hardening@lists.openwall.com
Cc: lasse.collin@tukaani.org
Link: http://lkml.kernel.org/r/1462825332-10505-6-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Baoquan He 2016-05-09 13:22:08 -07:00 committed by Ingo Molnar
parent 06486d6c97
commit 071a74930e
1 changed files with 28 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
arch/x86/boot/compressed/kaslr.c
View File

@ -417,8 +417,8 @@ static void process_e820_entry(struct e820entry *entry,
}
}
static unsigned long find_random_addr(unsigned long minimum,
unsigned long size)
static unsigned long find_random_phys_addr(unsigned long minimum,
unsigned long image_size)
{
int i;
unsigned long addr;
@ -428,12 +428,36 @@ static unsigned long find_random_addr(unsigned long minimum,
/* Verify potential e820 positions, appending to slots list. */
for (i = 0; i < boot_params->e820_entries; i++) {
process_e820_entry(&boot_params->e820_map[i], minimum, size);
process_e820_entry(&boot_params->e820_map[i], minimum,
image_size);
}
return slots_fetch_random();
}
static unsigned long find_random_virt_addr(unsigned long minimum,
unsigned long image_size)
{
unsigned long slots, random_addr;
/* Make sure minimum is aligned. */
minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
/* Align image_size for easy slot calculations. */
image_size = ALIGN(image_size, CONFIG_PHYSICAL_ALIGN);
/*
* There are how many CONFIG_PHYSICAL_ALIGN-sized slots
* that can hold image_size within the range of minimum to
* KERNEL_IMAGE_SIZE?
*/
slots = (KERNEL_IMAGE_SIZE - minimum - image_size) /
CONFIG_PHYSICAL_ALIGN + 1;
random_addr = get_random_long() % slots;
return random_addr * CONFIG_PHYSICAL_ALIGN + minimum;
}
/*
* Since this function examines addresses much more numerically,
* it takes the input and output pointers as 'unsigned long'.
@ -464,7 +488,7 @@ unsigned char *choose_random_location(unsigned long input,
mem_avoid_init(input, input_size, output);
/* Walk e820 and find a random address. */
random_addr = find_random_addr(output, output_size);
random_addr = find_random_phys_addr(output, output_size);
if (!random_addr) {
warn("KASLR disabled: could not find suitable E820 region!");
goto out;