[PATCH v2 07/15] x86, kaslr, 64bit: set new or extra ident_mapping

Yinghai Lu
2015-03-04T08:04:25Z

aslr will support to put random VO above 4G, so we need to set ident
mapping for the range even we come from startup_32 path.

At the same time, when boot from 64bit bootloader, bootloader will
set ident mapping, and boot via ZO startup_64.
Then pages for pagetable need to be avoided when selecting new random VO base.
otherwise decompressor will overwrite the pgtable.

One solution: go through pagetable and find out every page is
used by pagetable for every mem_aovid checking.
but kexec could put those page anywhere, and we will need extra code.

Other solution: create new ident mapping instead, and pages for pagetable
will sit in _pagetable area of ZO, and they are in mem_avoid array already.

so the _pgtable will be shared 32bit and 64bit path to reduce init_size.

Need to increase buffer size. As we need to cover old VO, params, cmdline
and new VO, in extreme case we could have all cross 512G boundary, will need
1+(2+2)*4 pages with 2M mapping.

Cc: Kees Cook <keescook@chromium.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Borislav Petkov <bp@suse.de>
Cc: Matt Fleming <matt.fleming@intel.com>
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
---
arch/x86/boot/compressed/aslr.c | 28 +++++++++++
arch/x86/boot/compressed/head_64.S | 4 +-
arch/x86/boot/compressed/misc_pgt.c | 96 +++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/boot.h | 13 +++++
4 files changed, 139 insertions(+), 2 deletions(-)
create mode 100644 arch/x86/boot/compressed/misc_pgt.c

diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
index e8486a5..10ed3c7 100644
--- a/arch/x86/boot/compressed/aslr.c
+++ b/arch/x86/boot/compressed/aslr.c
@@ -1,3 +1,8 @@
+#ifdef CONFIG_X86_64
+#define __pa(x) ((unsigned long)(x))
+#define __va(x) ((void *)((unsigned long)(x)))
+#endif
+
#include "misc.h"

#include <asm/msr.h>
@@ -21,6 +26,8 @@ struct kaslr_setup_data {
__u8 data[1];
} kaslr_setup_data;

+#include "misc_pgt.c"
+
#define I8254_PORT_CONTROL 0x43
#define I8254_PORT_COUNTER0 0x40
#define I8254_CMD_READBACK 0xC0
@@ -160,6 +167,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
unsafe = (unsigned long)input + input_size;
mem_avoid[0].start = unsafe;
mem_avoid[0].size = unsafe_len;
+ fill_linux64_pagetable(output, init_size);

/* Avoid initrd. */
initrd_start = (u64)real_mode->ext_ramdisk_image << 32;
@@ -168,6 +176,7 @@ static void mem_avoid_init(unsigned long input, unsigned long input_size,
initrd_size |= real_mode->hdr.ramdisk_size;
mem_avoid[1].start = initrd_start;
mem_avoid[1].size = initrd_size;
+ /* don't need to set mapping for initrd */

/* Avoid kernel command line. */
cmd_line = (u64)real_mode->ext_cmd_line_ptr << 32;
@@ -178,10 +187,25 @@ 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;
+ fill_linux64_pagetable(cmd_line, cmd_line_size);

/* Avoid params */
mem_avoid[3].start = (unsigned long)real_mode;
mem_avoid[3].size = sizeof(*real_mode);
+ fill_linux64_pagetable((unsigned long)real_mode, sizeof(*real_mode));
+}
+
+static void init_linux64_pagetable(void)
+{
+ struct setup_data *ptr;
+
+ ptr = (struct setup_data *)(unsigned long)real_mode->hdr.setup_data;
+ while (ptr) {
+ fill_linux64_pagetable((unsigned long)ptr,
+ sizeof(*ptr) + ptr->len);
+
+ ptr = (struct setup_data *)(unsigned long)ptr->next;
+ }
}

/* Does this memory vector overlap a known avoided area? */
@@ -346,6 +370,7 @@ unsigned char *choose_kernel_location(struct boot_params *params,
#endif
add_kaslr_setup_data(params, 1);

+ init_linux64_pagetable();
/* Record the various known unsafe memory ranges. */
mem_avoid_init((unsigned long)input, input_size,
(unsigned long)output, init_size);
@@ -362,6 +387,9 @@ unsigned char *choose_kernel_location(struct boot_params *params,
goto out;

choice = random;
+
+ fill_linux64_pagetable(choice, init_size);
+ switch_linux64_pagetable();
out:
return (unsigned char *)choice;
}
diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
index 69015b5..1b6e34a 100644
--- a/arch/x86/boot/compressed/head_64.S
+++ b/arch/x86/boot/compressed/head_64.S
@@ -125,7 +125,7 @@ ENTRY(startup_32)
/* Initialize Page tables to 0 */
leal pgtable(%ebx), %edi
xorl %eax, %eax
- movl $((4096*6)/4), %ecx
+ movl $(BOOT_INIT_PGT_SIZE/4), %ecx
rep stosl

/* Build Level 4 */
@@ -477,4 +477,4 @@ boot_stack_end:
.section ".pgtable","a",@nobits
.balign 4096
pgtable:
- .fill 6*4096, 1, 0
+ .fill BOOT_PGT_SIZE, 1, 0
diff --git a/arch/x86/boot/compressed/misc_pgt.c b/arch/x86/boot/compressed/misc_pgt.c
new file mode 100644
index 0000000..afc73bf
--- /dev/null
+++ b/arch/x86/boot/compressed/misc_pgt.c
@@ -0,0 +1,96 @@
+
+#ifdef CONFIG_X86_64
+#include <asm/init.h>
+#include <asm/pgtable.h>
+
+#include "../../mm/ident_map.c"
+
+struct alloc_pgt_data {
+ unsigned char *pgt_buf;
+ unsigned long pgt_buf_size;
+ unsigned long pgt_buf_offset;
+};
+
+static void *alloc_pgt_page(void *context)
+{
+ struct alloc_pgt_data *d = (struct alloc_pgt_data *)context;
+ unsigned char *p = (unsigned char *)d->pgt_buf;
+
+ if (d->pgt_buf_offset >= d->pgt_buf_size) {
+ debug_putstr("out of pgt_buf in misc.c\n");
+ return NULL;
+ }
+
+ p += d->pgt_buf_offset;
+ d->pgt_buf_offset += PAGE_SIZE;
+
+ return p;
+}
+
+/*
+ * Use a normal definition of memset() from string.c. There are already
+ * included header files which expect a definition of memset() and by
+ * the time we define memset macro, it is too late.
+ */
+#undef memset
+#define memzero(s, n) memset((s), 0, (n))
+
+unsigned long __force_order;
+static struct alloc_pgt_data pgt_data;
+static struct x86_mapping_info mapping_info;
+static pgd_t *level4p;
+
+extern unsigned char _pgtable[];
+static void fill_linux64_pagetable(unsigned long start, unsigned long size)
+{
+ unsigned long end = start + size;
+
+ if (!level4p) {
+ pgt_data.pgt_buf_offset = 0;
+ mapping_info.alloc_pgt_page = alloc_pgt_page;
+ mapping_info.context = &pgt_data;
+ mapping_info.pmd_flag = __PAGE_KERNEL_LARGE_EXEC;
+
+ /*
+ * come from startup_32 ?
+ * then cr3 is _pgtable, we can reuse it.
+ */
+ level4p = (pgd_t *)read_cr3();
+ if ((unsigned long)level4p == (unsigned long)_pgtable) {
+ pgt_data.pgt_buf = (unsigned char *)_pgtable +
+ BOOT_INIT_PGT_SIZE;
+ pgt_data.pgt_buf_size = BOOT_PGT_SIZE -
+ BOOT_INIT_PGT_SIZE;
+
+ debug_putstr("boot via startup_32\n");
+ } else {
+ pgt_data.pgt_buf = (unsigned char *)_pgtable;
+ pgt_data.pgt_buf_size = BOOT_PGT_SIZE;
+
+ debug_putstr("boot via startup_64\n");
+ level4p = (pgd_t *)alloc_pgt_page(&pgt_data);
+ }
+ memset((unsigned char *)pgt_data.pgt_buf, 0,
+ pgt_data.pgt_buf_size);
+ }
+
+ /* align boundary to 2M */
+ start = round_down(start, PMD_SIZE);
+ end = round_up(end, PMD_SIZE);
+ if (start < end)
+ kernel_ident_mapping_init(&mapping_info, level4p, start, end);
+}
+
+static void switch_linux64_pagetable(void)
+{
+ write_cr3((unsigned long)level4p);
+}
+
+#else
+static void fill_linux64_pagetable(unsigned long start, unsigned long size)
+{
+}
+static void switch_linux64_pagetable(void)
+{
+}
+#endif
diff --git a/arch/x86/include/asm/boot.h b/arch/x86/include/asm/boot.h
index 4fa687a..3795a77 100644
--- a/arch/x86/include/asm/boot.h
+++ b/arch/x86/include/asm/boot.h
@@ -32,7 +32,20 @@
#endif /* !CONFIG_KERNEL_BZIP2 */

#ifdef CONFIG_X86_64
+
#define BOOT_STACK_SIZE 0x4000
+
+#define BOOT_INIT_PGT_SIZE (6*4096)
+#ifdef CONFIG_RANDOMIZE_BASE
+/*
+ * 17 pages to cover for kernel, param, cmd_line, random kernel
+ * if all cross 512G boundary.
+ */
+#define BOOT_PGT_SIZE (BOOT_INIT_PGT_SIZE + (11*4096))
+#else
+#define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
+#endif
+
#else
#define BOOT_STACK_SIZE 0x1000
#endif
--
1.8.4.5