From: Yinghai Lu <ying...@kernel.org>
We are going to support kaslr with 64bit above 4G, and new random output
could be anywhere. Array mem_avoid is used for kaslr to search new output
address. Current code only track range that is after output+output_size.
So we need to track all ranges instead of just after output+output_size.
Current code has first entry which is extra bytes before input+input_size,
and it is according to output_size. Other entries are for initrd, cmdline,
and heap/stack for ZO running.
At first, let's check the first entry that should be in the mem_avoid array.
Now ZO sit end of the buffer always, we can find out where is text and
data/bss etc of ZO.
Since init_size >= run_size, and input+input_len >= output+output_len,
here make several assumptions for better presentation by graph:
- init_size > run_size
- input+input_len > output+output_len
- run_size > output_len
0 output input input+input_len
output+init_size
| | | |
|
|-----|-------------------|--------|------------------|----|------------|----------|
| | |
output+init_size-ZO_INIT_SIZE output+output_len
output+run_size
[output, output+init_size) is the for decompressing buffer for compressed
kernel.
[output, output+run_size) is for VO run size.
[output, output+output_len) is (VO (vmlinux after objcopy) plus relocs)
[output+init_size-ZO_INIT_SIZE, output+init_size) is copied ZO.
[input, input+input_len) is copied compressed (VO (vmlinux after objcopy)
plus relocs), not the ZO.
[input+input_len, output+init_size) is [_text, _end) for ZO. that could be
first range in mem_avoid. Now the new first entry already includes heap and
stack for ZO running. So no need to put them separately into mem_avoid array.
Also [input, input+input_size) need be put in mem_avoid array. It is adjacent
to new first entry, so merge them.
At last we need to put boot_params into the mem_avoid too. As with 64bit
bootloader could put it anywhere.
After these changes, we have all ranges which need be avoided in mem_avoid
array.
Cc: Kees Cook <keesc...@chromium.org>
Signed-off-by: Yinghai Lu <ying...@kernel.org>
---
v2->v3:
Adjust the patch log.
arch/x86/boot/compressed/aslr.c | 29 +++++++++++++----------------
1 file changed, 13 insertions(+), 16 deletions(-)
diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index 622aa88..b93be03 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -109,7 +109,7 @@ struct mem_vector {
unsigned long size;
};
-#define MEM_AVOID_MAX 5
+#define MEM_AVOID_MAX 4
static struct mem_vector mem_avoid[MEM_AVOID_MAX];
static bool mem_contains(struct mem_vector *region, struct mem_vector *item)
@@ -135,21 +135,22 @@ static bool mem_overlaps(struct mem_vector *one, struct
mem_vector *two)
}
static void mem_avoid_init(unsigned long input, unsigned long input_size,
- unsigned long output, unsigned long output_size)
+ unsigned long output)
{
+ unsigned long init_size = real_mode->hdr.init_size;
u64 initrd_start, initrd_size;
u64 cmd_line, cmd_line_size;
- unsigned long unsafe, unsafe_len;
char *ptr;
/*
* Avoid the region that is unsafe to overlap during
- * decompression (see calculations at top of misc.c).
+ * decompression.
+ * As we already move ZO (arch/x86/boot/compressed/vmlinux)
+ * to the end of buffer, [input+input_size, output+init_size)
+ * has [_text, _end) for ZO.
*/
- unsafe_len = (output_size >> 12) + 32768 + 18;
- unsafe = (unsigned long)input + input_size - unsafe_len;
- mem_avoid[0].start = unsafe;
- mem_avoid[0].size = unsafe_len;
+ mem_avoid[0].start = input;
+ mem_avoid[0].size = (output + init_size) - input;
/* Avoid initrd. */
initrd_start = (u64)real_mode->ext_ramdisk_image << 32;
@@ -169,13 +170,9 @@ static void mem_avoid_init(unsigned long input, unsigned
long input_size,
mem_avoid[2].start = cmd_line;
mem_avoid[2].size = cmd_line_size;
- /* Avoid heap memory. */
- mem_avoid[3].start = (unsigned long)free_mem_ptr;
- mem_avoid[3].size = BOOT_HEAP_SIZE;
-
- /* Avoid stack memory. */
- mem_avoid[4].start = (unsigned long)free_mem_end_ptr;
- mem_avoid[4].size = BOOT_STACK_SIZE;
+ /* Avoid params */
+ mem_avoid[3].start = (unsigned long)real_mode;
+ mem_avoid[3].size = sizeof(*real_mode);
}
/* Does this memory vector overlap a known avoided area? */
@@ -319,7 +316,7 @@ unsigned char *choose_kernel_location(unsigned char *input,
/* Record the various known unsafe memory ranges. */
mem_avoid_init((unsigned long)input, input_size,
- (unsigned long)output, output_size);
+ (unsigned long)output);
/* Walk e820 and find a random address. */
random = find_random_addr(choice, output_size);
--
2.5.0
