Re: [PATCH v3 7/7] x86, kaslr, 64bit: Set new or extra ident_mapping

[Yinghai Lu <yinghai@kernel.org>]

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On Mon, Mar 9, 2015 at 6:14 PM, Yinghai Lu <yinghai@kernel.org> wrote:
>>>
>>> +#include "misc_pgt.c"
>>
>> Shouldn't this just be a normal built .o file that is linked together
>> in the Makefile, specifically tracking CONFIG_RANDOMIZE_BASE as aslr.o
>> already is?
>
> Yes, we could go that way.

Please check attached version with link misc_pgt.o.

BTW, here are difference between include misc_pgt.c and link misc_pgt.o:

include misc_pgt.c
   text       data        bss        dec        hex    filename
13934290        304      50064    13984658     d56392
arch/x86/boot/compressed/vmlinux

link misc_pgt.o
   text       data        bss        dec        hex    filename
13934336        304      50064    13984704     d563c0
arch/x86/boot/compressed/vmlinux

Thanks

Yinghai

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[-- Type: text/x-patch, Size: 9231 bytes --]

From: Yinghai Lu <yinghai@kernel.org>
Subject: [PATCH v4] x86, kaslr, 64bit: Set new or extra ident_mapping

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

Second, when boot from 64bit bootloader, bootloader set ident mapping,
and boot via ZO (arch/x86/boot/compressed/vmlinux) startup_64.
Those pages for pagetable need to be avoided when we select new random
VO (vmlinux) base. Otherwise decompressor would overwrite them during
decompressing.

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

Other solution: create new ident mapping instead, and pages for pagetable
will sit in _pagetable section of ZO, and they are in mem_avoid array already.
In this way, we can reuse the code for setting ident mapping.

The _pgtable will be shared 32bit and 64bit path to reduce init_size,
as now ZO _rodata to _end will contribute init_size.

Need to increase pgt buffer size.
When boot via startup_64, as we need to cover old VO, params, cmdline
and new VO, in extreme case we could have them all cross 512G boundary,
will need (2+2)*4 pages with 2M mapping. And need 2 for first 2M for vga ram.
Plus one for level4. Total will be 19 pages.
When boot via startup_32, aslr would move new VO above 4G, we need set extra
ident mapping for new VO, pgt buffer come from _pgtable offset 6 pages.
should only need (2+2) pages at most when it cross 512G boundary.
So 19 pages could make both paths happy.

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>

---
-v3: add mapping for first 2M with video ram when X86_VERBOSE_BOOTUP is set.
     Don't need to set mapping for setup_data, as it is already late
     in boot/ZO stage, will not access it until VO stage, and VO stage
     will use early_memmap or kernel address to access them.
-v4: link misc_pgt.o instead of including misc_pgt.c in aslr.c up to request
     from Kees.

---
 arch/x86/boot/compressed/Makefile   |    3 +
 arch/x86/boot/compressed/aslr.c     |   14 +++++
 arch/x86/boot/compressed/head_64.S  |    4 -
 arch/x86/boot/compressed/misc.h     |   11 ++++
 arch/x86/boot/compressed/misc_pgt.c |   91 ++++++++++++++++++++++++++++++++++++
 arch/x86/include/asm/boot.h         |   19 +++++++
 6 files changed, 140 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/boot/compressed/misc_pgt.c
===================================================================
--- /dev/null
+++ linux-2.6/arch/x86/boot/compressed/misc_pgt.c
@@ -0,0 +1,91 @@
+#define __pa(x)  ((unsigned long)(x))
+#define __va(x)  ((void *)((unsigned long)(x)))
+
+#include "misc.h"
+
+#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;
+
+void fill_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)
+		return;
+
+	kernel_ident_mapping_init(&mapping_info, level4p, start, end);
+}
+
+void switch_pagetable(void)
+{
+	write_cr3((unsigned long)level4p);
+}
Index: linux-2.6/arch/x86/boot/compressed/aslr.c
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/aslr.c
+++ linux-2.6/arch/x86/boot/compressed/aslr.c
@@ -160,6 +160,7 @@ static void mem_avoid_init(unsigned long
 	unsafe = (unsigned long)input + input_size;
 	mem_avoid[0].start = unsafe;
 	mem_avoid[0].size = unsafe_len;
+	fill_pagetable(output, init_size);
 
 	/* Avoid initrd. */
 	initrd_start  = (u64)real_mode->ext_ramdisk_image << 32;
@@ -168,6 +169,7 @@ static void mem_avoid_init(unsigned long
 	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 +180,19 @@ static void mem_avoid_init(unsigned long
 		;
 	mem_avoid[2].start = cmd_line;
 	mem_avoid[2].size = cmd_line_size;
+	fill_pagetable(cmd_line, cmd_line_size);
 
 	/* Avoid params */
 	mem_avoid[3].start = (unsigned long)real_mode;
 	mem_avoid[3].size = sizeof(*real_mode);
+	fill_pagetable((unsigned long)real_mode, sizeof(*real_mode));
+
+	/* don't need to set mapping for setup_data */
+
+#ifdef CONFIG_X86_VERBOSE_BOOTUP
+	/* for video ram */
+	fill_pagetable(0, PMD_SIZE);
+#endif
 }
 
 /* Does this memory vector overlap a known avoided area? */
@@ -362,6 +373,9 @@ unsigned char *choose_kernel_location(st
 		goto out;
 
 	choice = random;
+
+	fill_pagetable(choice, init_size);
+	switch_pagetable();
 out:
 	return (unsigned char *)choice;
 }
Index: linux-2.6/arch/x86/boot/compressed/head_64.S
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/head_64.S
+++ linux-2.6/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
Index: linux-2.6/arch/x86/include/asm/boot.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/boot.h
+++ linux-2.6/arch/x86/include/asm/boot.h
@@ -32,7 +32,26 @@
 #endif /* !CONFIG_KERNEL_BZIP2 */
 
 #ifdef CONFIG_X86_64
+
 #define BOOT_STACK_SIZE	0x4000
+
+#define BOOT_INIT_PGT_SIZE (6*4096)
+#ifdef CONFIG_RANDOMIZE_BASE
+/*
+ * 1 page for level4, 2 pages for first 2M.
+ * (2+2)*4 pages for kernel, param, cmd_line, random kernel
+ * if all cross 512G boundary.
+ * So total will be 19 pages.
+ */
+#ifdef CONFIG_X86_VERBOSE_BOOTUP
+#define BOOT_PGT_SIZE (19*4096)
+#else
+#define BOOT_PGT_SIZE (17*4096)
+#endif
+#else
+#define BOOT_PGT_SIZE BOOT_INIT_PGT_SIZE
+#endif
+
 #else
 #define BOOT_STACK_SIZE	0x1000
 #endif
Index: linux-2.6/arch/x86/boot/compressed/Makefile
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/Makefile
+++ linux-2.6/arch/x86/boot/compressed/Makefile
@@ -46,6 +46,9 @@ vmlinux-objs-y := $(obj)/vmlinux.lds $(o
 
 vmlinux-objs-$(CONFIG_EARLY_PRINTK) += $(obj)/early_serial_console.o
 vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/aslr.o
+ifdef CONFIG_X86_64
+	vmlinux-objs-$(CONFIG_RANDOMIZE_BASE) += $(obj)/misc_pgt.o
+endif
 
 $(obj)/eboot.o: KBUILD_CFLAGS += -fshort-wchar -mno-red-zone
 
Index: linux-2.6/arch/x86/boot/compressed/misc.h
===================================================================
--- linux-2.6.orig/arch/x86/boot/compressed/misc.h
+++ linux-2.6/arch/x86/boot/compressed/misc.h
@@ -76,6 +76,17 @@ unsigned char *choose_kernel_location(st
 }
 #endif
 
+#ifdef CONFIG_X86_64
+void fill_pagetable(unsigned long start, unsigned long size);
+void switch_pagetable(void);
+extern unsigned char _pgtable[];
+#else
+static inline void fill_pagetable(unsigned long start, unsigned long size)
+{ }
+static inline void switch_pagetable(void)
+{ }
+#endif
+
 #ifdef CONFIG_EARLY_PRINTK
 /* early_serial_console.c */
 extern int early_serial_base;