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x86: Add NX protection for kernel data 

This patch expands functionality of CONFIG_DEBUG_RODATA to set main
(static) kernel data area as NX.

The following steps are taken to achieve this:

 1. Linker script is adjusted so .text always starts and ends on a page bound
 2. Linker script is adjusted so .rodata always start and end on a page boundary
 3. NX is set for all pages from _etext through _end in mark_rodata_ro.
 4. free_init_pages() sets released memory NX in arch/x86/mm/init.c
 5. bios rom is set to x when pcibios is used.

The results of patch application may be observed in the diff of kernel page
table dumps:

pcibios:

 -- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
 ++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
  0x00000000-0xc0000000           3G                           pmd
  ---[ Kernel Mapping ]---
 -0xc0000000-0xc0100000           1M     RW             GLB x  pte
 +0xc0000000-0xc00a0000         640K     RW             GLB NX pte
 +0xc00a0000-0xc0100000         384K     RW             GLB x  pte
 -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
 +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
 +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
 -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
 +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
  0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
  0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
  0xf7bfe000-0xf7c00000           8K                           pte

No pcibios:

 -- data_nx_pt_before.txt       2009-10-13 07:48:59.000000000 -0400
 ++ data_nx_pt_after.txt        2009-10-13 07:26:46.000000000 -0400
  0x00000000-0xc0000000           3G                           pmd
  ---[ Kernel Mapping ]---
 -0xc0000000-0xc0100000           1M     RW             GLB x  pte
 +0xc0000000-0xc0100000           1M     RW             GLB NX pte
 -0xc0100000-0xc03d7000        2908K     ro             GLB x  pte
 +0xc0100000-0xc0318000        2144K     ro             GLB x  pte
 +0xc0318000-0xc03d7000         764K     ro             GLB NX pte
 -0xc03d7000-0xc0600000        2212K     RW             GLB x  pte
 +0xc03d7000-0xc0600000        2212K     RW             GLB NX pte
  0xc0600000-0xf7a00000         884M     RW         PSE GLB NX pmd
  0xf7a00000-0xf7bfe000        2040K     RW             GLB NX pte
  0xf7bfe000-0xf7c00000           8K                           pte

The patch has been originally developed for Linux 2.6.34-rc2 x86 by
Siarhei Liakh <sliakh.lkml@gmail.com> and Xuxian Jiang <jiang@cs.ncsu.edu>.

 -v1:  initial patch for 2.6.30
 -v2:  patch for 2.6.31-rc7
 -v3:  moved all code into arch/x86, adjusted credits
 -v4:  fixed ifdef, removed credits from CREDITS
 -v5:  fixed an address calculation bug in mark_nxdata_nx()
 -v6:  added acked-by and PT dump diff to commit log
 -v7:  minor adjustments for -tip
 -v8:  rework with the merge of "Set first MB as RW+NX"

Signed-off-by: Siarhei Liakh <sliakh.lkml@gmail.com>
Signed-off-by: Xuxian Jiang <jiang@cs.ncsu.edu>
Signed-off-by: Matthieu CASTET <castet.matthieu@free.fr>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: James Morris <jmorris@namei.org>
Cc: Andi Kleen <ak@muc.de>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Dave Jones <davej@redhat.com>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <4CE2F82E.60601@free.fr>
[ minor cleanliness edits ]
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Matthieu Castet 2010-11-16 22:31:26 +01:00 committed by Ingo Molnar
parent 64edc8ed5f
commit 5bd5a45266
7 changed files with 57 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
arch/x86/include/asm/pci.h
View File

@ -65,6 +65,7 @@ extern unsigned long pci_mem_start;
#define PCIBIOS_MIN_CARDBUS_IO 0x4000
extern int pcibios_enabled;
void pcibios_config_init(void);
struct pci_bus *pcibios_scan_root(int bus);

8
arch/x86/kernel/vmlinux.lds.S
View File

@ -69,7 +69,7 @@ jiffies_64 = jiffies;
PHDRS {
text PT_LOAD FLAGS(5); /* R_E */
data PT_LOAD FLAGS(7); /* RWE */
data PT_LOAD FLAGS(6); /* RW_ */
#ifdef CONFIG_X86_64
user PT_LOAD FLAGS(5); /* R_E */
#ifdef CONFIG_SMP
@ -116,6 +116,10 @@ SECTIONS
EXCEPTION_TABLE(16) :text = 0x9090
#if defined(CONFIG_DEBUG_RODATA)
/* .text should occupy whole number of pages */
. = ALIGN(PAGE_SIZE);
#endif
X64_ALIGN_DEBUG_RODATA_BEGIN
RO_DATA(PAGE_SIZE)
X64_ALIGN_DEBUG_RODATA_END
@ -335,7 +339,7 @@ SECTIONS
__bss_start = .;
*(.bss..page_aligned)
*(.bss)
. = ALIGN(4);
. = ALIGN(PAGE_SIZE);
__bss_stop = .;
}

3
arch/x86/mm/init.c
View File

@ -364,8 +364,9 @@ void free_init_pages(char *what, unsigned long begin, unsigned long end)
/*
* We just marked the kernel text read only above, now that
* we are going to free part of that, we need to make that
* writeable first.
* writeable and non-executable first.
*/
set_memory_nx(begin, (end - begin) >> PAGE_SHIFT);
set_memory_rw(begin, (end - begin) >> PAGE_SHIFT);
printk(KERN_INFO "Freeing %s: %luk freed\n", what, (end - begin) >> 10);

20
arch/x86/mm/init_32.c
View File

@ -226,7 +226,7 @@ page_table_range_init(unsigned long start, unsigned long end, pgd_t *pgd_base)
static inline int is_kernel_text(unsigned long addr)
{
if (addr >= PAGE_OFFSET && addr <= (unsigned long)__init_end)
if (addr >= (unsigned long)_text && addr <= (unsigned long)__init_end)
return 1;
return 0;
}
@ -912,6 +912,23 @@ void set_kernel_text_ro(void)
set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
}
static void mark_nxdata_nx(void)
{
/*
* When this called, init has already been executed and released,
* so everything past _etext sould be NX.
*/
unsigned long start = PFN_ALIGN(_etext);
/*
* This comes from is_kernel_text upper limit. Also HPAGE where used:
*/
unsigned long size = (((unsigned long)__init_end + HPAGE_SIZE) & HPAGE_MASK) - start;
if (__supported_pte_mask & _PAGE_NX)
printk(KERN_INFO "NX-protecting the kernel data: %luk\n", size >> 10);
set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
}
void mark_rodata_ro(void)
{
unsigned long start = PFN_ALIGN(_text);
@ -946,6 +963,7 @@ void mark_rodata_ro(void)
printk(KERN_INFO "Testing CPA: write protecting again\n");
set_pages_ro(virt_to_page(start), size >> PAGE_SHIFT);
#endif
mark_nxdata_nx();
}
#endif

3
arch/x86/mm/init_64.c
View File

@ -788,6 +788,7 @@ void mark_rodata_ro(void)
unsigned long rodata_start =
((unsigned long)__start_rodata + PAGE_SIZE - 1) & PAGE_MASK;
unsigned long end = (unsigned long) &__end_rodata_hpage_align;
unsigned long kernel_end = (((unsigned long)&__init_end + HPAGE_SIZE) & HPAGE_MASK);
unsigned long text_end = PAGE_ALIGN((unsigned long) &__stop___ex_table);
unsigned long rodata_end = PAGE_ALIGN((unsigned long) &__end_rodata);
unsigned long data_start = (unsigned long) &_sdata;
@ -802,7 +803,7 @@ void mark_rodata_ro(void)
* The rodata section (but not the kernel text!) should also be
* not-executable.
*/
set_memory_nx(rodata_start, (end - rodata_start) >> PAGE_SHIFT);
set_memory_nx(rodata_start, (kernel_end - rodata_start) >> PAGE_SHIFT);
rodata_test();

5
arch/x86/mm/pageattr.c
View File

@ -13,6 +13,7 @@
#include <linux/pfn.h>
#include <linux/percpu.h>
#include <linux/gfp.h>
#include <linux/pci.h>
#include <asm/e820.h>
#include <asm/processor.h>
@ -261,8 +262,10 @@ static inline pgprot_t static_protections(pgprot_t prot, unsigned long address,
* The BIOS area between 640k and 1Mb needs to be executable for
* PCI BIOS based config access (CONFIG_PCI_GOBIOS) support.
*/
if (within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
#ifdef CONFIG_PCI_BIOS
if (pcibios_enabled && within(pfn, BIOS_BEGIN >> PAGE_SHIFT, BIOS_END >> PAGE_SHIFT))
pgprot_val(forbidden) |= _PAGE_NX;
#endif
/*
* The kernel text needs to be executable for obvious reasons

23
arch/x86/pci/pcbios.c
View File

@ -9,6 +9,7 @@
#include <linux/uaccess.h>
#include <asm/pci_x86.h>
#include <asm/pci-functions.h>
#include <asm/cacheflush.h>
/* BIOS32 signature: "_32_" */
#define BIOS32_SIGNATURE (('_' << 0) + ('3' << 8) + ('2' << 16) + ('_' << 24))
@ -25,6 +26,27 @@
#define PCIBIOS_HW_TYPE1_SPEC 0x10
#define PCIBIOS_HW_TYPE2_SPEC 0x20
int pcibios_enabled;
/* According to the BIOS specification at:
* http://members.datafast.net.au/dft0802/specs/bios21.pdf, we could
* restrict the x zone to some pages and make it ro. But this may be
* broken on some bios, complex to handle with static_protections.
* We could make the 0xe0000-0x100000 range rox, but this can break
* some ISA mapping.
*
* So we let's an rw and x hole when pcibios is used. This shouldn't
* happen for modern system with mmconfig, and if you don't want it
* you could disable pcibios...
*/
static inline void set_bios_x(void)
{
pcibios_enabled = 1;
set_memory_x(PAGE_OFFSET + BIOS_BEGIN, (BIOS_END - BIOS_BEGIN) >> PAGE_SHIFT);
if (__supported_pte_mask & _PAGE_NX)
printk(KERN_INFO "PCI : PCI BIOS aera is rw and x. Use pci=nobios if you want it NX.\n");
}
/*
* This is the standard structure used to identify the entry point
* to the BIOS32 Service Directory, as documented in
@ -332,6 +354,7 @@ static struct pci_raw_ops * __devinit pci_find_bios(void)
DBG("PCI: BIOS32 Service Directory entry at 0x%lx\n",
bios32_entry);
bios32_indirect.address = bios32_entry + PAGE_OFFSET;
set_bios_x();
if (check_pcibios())
return &pci_bios_access;
}