linux-kernel - [PATCH v3 08/19] x86, kaslr: Consolidate mem

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Date:	Sat,  5 Mar 2016 00:25:06 +0800
From:	Baoquan He <bhe@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	yinghai@...nel.org, keescook@...omium.org, hpa@...or.com,
	vgoyal@...hat.com, mingo@...hat.com, bp@...en8.de, luto@...nel.org,
	lasse.collin@...aani.org, akpm@...ux-foundation.org,
	dyoung@...hat.com
Subject: [PATCH v3 08/19] x86, kaslr: Consolidate mem_avoid array filling

From: Yinghai Lu <yinghai@...nel.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 <keescook@...omium.org>
Signed-off-by: Yinghai Lu <yinghai@...nel.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