[PATCH v3 5/7] x86, kaslr: Consolidate mem_avoid array filling

Yinghai Lu
2015-03-07T22:07:19Z

Now ZO sit end of the buffer, we can find out where is ZO text
and data/bss etc.

[input, input+input_size) is copied compressed kernel, not the whole ZO.
[output, output+init_size) is the buffer for VO.

[input+input_size, output+init_size) is [_text, _end) for ZO.
that could be first range in mem_avoid. We don't need to guess that anymore.

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

We need to put boot_params into the mem_avoid too. As with 64bit bootloader
could put it anywhere.

Also change output_size referring to init_size, as we pass init_size instead.

Cc: Kees Cook <keescook-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
Signed-off-by: Yinghai Lu <yinghai-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
arch/x86/boot/compressed/aslr.c | 29 ++++++++++++++---------------
arch/x86/boot/compressed/misc.h | 4 ++--
2 files changed, 16 insertions(+), 17 deletions(-)

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index 7083c16..a279514 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -116,7 +116,7 @@ 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)
@@ -142,7 +142,7 @@ 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)
{
u64 initrd_start, initrd_size;
u64 cmd_line, cmd_line_size;
@@ -151,10 +151,13 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,

/*
* 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;
+ unsafe_len = output + init_size - (input + input_size);
+ unsafe = (unsigned long)input + input_size;
mem_avoid[0].start = unsafe;
mem_avoid[0].size = unsafe_len;

@@ -176,13 +179,9 @@ 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? */
@@ -327,7 +326,7 @@ unsigned char *choose_kernel_location(struct boot_params *params,
unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size)
+ unsigned long init_size)
{
unsigned long choice = (unsigned long)output;
unsigned long random;
@@ -349,10 +348,10 @@ unsigned char *choose_kernel_location(struct boot_params *params,

/* Record the various known unsafe memory ranges. */
mem_avoid_init((unsigned long)input, input_size,
- (unsigned long)output, output_size);
+ (unsigned long)output, init_size);

/* Walk e820 and find a random address. */
- random = find_random_addr(choice, output_size);
+ random = find_random_addr(choice, init_size);
if (!random) {
debug_putstr("KASLR could not find suitable E820 region...\n");
goto out;
diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
index ee3576b..23156e7 100644
--- a/arch/x86/boot/compressed/misc.h
+++ b/arch/x86/boot/compressed/misc.h
@@ -61,7 +61,7 @@ unsigned char *choose_kernel_location(struct boot_params *params,
unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size);
+ unsigned long init_size);
/* cpuflags.c */
bool has_cpuflag(int flag);
#else
@@ -70,7 +70,7 @@ unsigned char *choose_kernel_location(struct boot_params *params,
unsigned char *input,
unsigned long input_size,
unsigned char *output,
- unsigned long output_size)
+ unsigned long init_size)
{
return output;
}
--
1.8.4.5