[PATCH v5 06/19] x86, kaslr: Consolidate mem_avoid array filling

Yinghai Lu
2015-03-18T07:28:13Z

We are going to support kaslr with 64bit above 4G, and new random output
buffer could be anywhere.

mem_avoid array is used for kaslr to search new output buffer.
Current code only track range that is after output+output_run_size.

We need to track all range not just after output+output_run_size.

Current code has first entry is extra bytes after input+input_size, and it
is according to output_run_size. Other entries are for initrd, cmdline,
and heap/stack for ZO running.

At first, 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 ZO text
and data/bss etc.
output+run_size
|
0 output input input+input_size | output+init_size
| | | | | |
|-----|-----------------|--|---------------|------|---|----------|
| |
output+init_size-ZO_SIZE output+output_size

[output, output+init_size) is the buffer for decompress.

[output, output+run_size) is for VO run size.
[output, output+output_size) is (VO (vmlinux after objcopy) plus relocs)

[output+init_size-ZO_SIZE, output+init_size) is copied ZO.
[input, input+input_size) is copied compressed (VO (vmlinux after objcopy)
plus relocs), not the ZO.

[input+input_size, output+init_size) is [_text, _end) for ZO. that could be
first range in mem_avoid.

That new first entry already include heap and stack for ZO running. So we
don't need to put them separatedly into mem_avoid array.

Also we need to put [input, input+input_size) in mem_avoid array, ant it
is connected to first one, 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 those changes, we have all range needed to be avoided in mem_avoid array.

Cc: Kees Cook <keescook@chromium.org>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
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 5dc1a65..9dab0d6 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -112,7 +112,7 @@ 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)
@@ -138,21 +138,22 @@ 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_run_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_run_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;
@@ -172,13 +173,9 @@ 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? */
@@ -343,7 +340,7 @@ 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_run_size);
+ (unsigned long)output);

/* Walk e820 and find a random address. */
random = find_random_addr(choice, output_run_size);
--
1.8.4.5