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[PATCH] x86: tighten kernel image page access rights

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On x86-64, kernel memory freed after init can be entirely unmapped instead
of just getting 'poisoned' by overwriting with a debug pattern.

On i386 and x86-64 (under CONFIG_DEBUG_RODATA), kernel text and bug table
can also be write-protected.

Compared to the first version, this one prevents re-creating deleted
mappings in the kernel image range on x86-64, if those got removed
previously. This, together with the original changes, prevents temporarily
having inconsistent mappings when cacheability attributes are being
changed on such pages (e.g. from AGP code). While on i386 such duplicate
mappings don't exist, the same change is done there, too, both for
consistency and because checking pte_present() before using various other
pte_XXX functions is a requirement anyway. At once, i386 code gets
adjusted to use pte_huge() instead of open coding this.

AK: split out cpa() changes

Signed-off-by: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Jan Beulich 2007-05-02 19:27:10 +02:00 committed by Andi Kleen
parent d01ad8dd56
commit 6fb14755a6
6 changed files with 40 additions and 23 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
arch/i386/kernel/vmlinux.lds.S
View File

@ -61,8 +61,6 @@ SECTIONS
__stop___ex_table = .;
}
RODATA
BUG_TABLE
. = ALIGN(4);
@ -72,6 +70,8 @@ SECTIONS
__tracedata_end = .;
}
RODATA
/* writeable */
. = ALIGN(4096);
.data : AT(ADDR(.data) - LOAD_OFFSET) { /* Data */

25
arch/i386/mm/init.c
View File

@ -22,6 +22,7 @@
#include <linux/init.h>
#include <linux/highmem.h>
#include <linux/pagemap.h>
#include <linux/pfn.h>
#include <linux/poison.h>
#include <linux/bootmem.h>
#include <linux/slab.h>
@ -751,13 +752,25 @@ static int noinline do_test_wp_bit(void)
void mark_rodata_ro(void)
{
unsigned long addr = (unsigned long)__start_rodata;
unsigned long start = PFN_ALIGN(_text);
unsigned long size = PFN_ALIGN(_etext) - start;
for (; addr < (unsigned long)__end_rodata; addr += PAGE_SIZE)
change_page_attr(virt_to_page(addr), 1, PAGE_KERNEL_RO);
#ifdef CONFIG_HOTPLUG_CPU
/* It must still be possible to apply SMP alternatives. */
if (num_possible_cpus() <= 1)
#endif
{
change_page_attr(virt_to_page(start),
size >> PAGE_SHIFT, PAGE_KERNEL_RX);
printk("Write protecting the kernel text: %luk\n", size >> 10);
}
printk("Write protecting the kernel read-only data: %uk\n",
(__end_rodata - __start_rodata) >> 10);
start += size;
size = (unsigned long)__end_rodata - start;
change_page_attr(virt_to_page(start),
size >> PAGE_SHIFT, PAGE_KERNEL_RO);
printk("Write protecting the kernel read-only data: %luk\n",
size >> 10);
/*
* change_page_attr() requires a global_flush_tlb() call after it.
@ -781,7 +794,7 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
__free_page(page);
totalram_pages++;
}
printk(KERN_INFO "Freeing %s: %ldk freed\n", what, (end - begin) >> 10);
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
}
void free_initmem(void)

1
arch/x86_64/kernel/head.S
View File

@ -280,7 +280,6 @@ early_idt_ripmsg:
.balign PAGE_SIZE
ENTRY(stext)
ENTRY(_stext)
#define NEXT_PAGE(name) \
.balign PAGE_SIZE; \

5
arch/x86_64/kernel/vmlinux.lds.S
View File

@ -29,6 +29,7 @@ SECTIONS
.text : AT(ADDR(.text) - LOAD_OFFSET) {
/* First the code that has to be first for bootstrapping */
*(.bootstrap.text)
_stext = .;
/* Then all the functions that are "hot" in profiles, to group them
onto the same hugetlb entry */
#include "functionlist"
@ -50,10 +51,10 @@ SECTIONS
__ex_table : AT(ADDR(__ex_table) - LOAD_OFFSET) { *(__ex_table) }
__stop___ex_table = .;
RODATA
BUG_TABLE
RODATA
. = ALIGN(PAGE_SIZE); /* Align data segment to page size boundary */
/* Data */
.data : AT(ADDR(.data) - LOAD_OFFSET) {

25
arch/x86_64/mm/init.c
View File

@ -22,6 +22,7 @@
#include <linux/bootmem.h>
#include <linux/proc_fs.h>
#include <linux/pci.h>
#include <linux/pfn.h>
#include <linux/poison.h>
#include <linux/dma-mapping.h>
#include <linux/module.h>
@ -563,21 +564,23 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
if (begin >= end)
return;
printk(KERN_INFO "Freeing %s: %ldk freed\n", what, (end - begin) >> 10);
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);
for (addr = begin; addr < end; addr += PAGE_SIZE) {
struct page *page = pfn_to_page(addr >> PAGE_SHIFT);
ClearPageReserved(page);
init_page_count(page);
memset(page_address(page), POISON_FREE_INITMEM, PAGE_SIZE);
if (addr >= __START_KERNEL_map)
change_page_attr_addr(addr, 1, __pgprot(0));
__free_page(page);
totalram_pages++;
}
if (addr > __START_KERNEL_map)
global_flush_tlb();
}
void free_initmem(void)
{
memset(__initdata_begin, POISON_FREE_INITDATA,
__initdata_end - __initdata_begin);
free_init_pages("unused kernel memory",
__pa_symbol(&__init_begin),
__pa_symbol(&__init_end));
@ -587,14 +590,18 @@ void free_initmem(void)
void mark_rodata_ro(void)
{
unsigned long addr = (unsigned long)__va(__pa_symbol(&__start_rodata));
unsigned long end = (unsigned long)__va(__pa_symbol(&__end_rodata));
unsigned long start = PFN_ALIGN(__va(__pa_symbol(&_stext))), size;
for (; addr < end; addr += PAGE_SIZE)
change_page_attr_addr(addr, 1, PAGE_KERNEL_RO);
#ifdef CONFIG_HOTPLUG_CPU
/* It must still be possible to apply SMP alternatives. */
if (num_possible_cpus() > 1)
start = PFN_ALIGN(__va(__pa_symbol(&_etext)));
#endif
size = (unsigned long)__va(__pa_symbol(&__end_rodata)) - start;
change_page_attr_addr(start, size >> PAGE_SHIFT, PAGE_KERNEL_RO);
printk ("Write protecting the kernel read-only data: %luk\n",
(__end_rodata - __start_rodata) >> 10);
printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
size >> 10);
/*
* change_page_attr_addr() requires a global_flush_tlb() call after it.

3
include/linux/poison.h
View File

@ -26,9 +26,6 @@
/********** arch/$ARCH/mm/init.c **********/
#define POISON_FREE_INITMEM 0xcc
/********** arch/x86_64/mm/init.c **********/
#define POISON_FREE_INITDATA 0xba
/********** arch/ia64/hp/common/sba_iommu.c **********/
/*
* arch/ia64/hp/common/sba_iommu.c uses a 16-byte poison string with a