[PATCH] [35/48] x86: tighten kernel image page access rights

From: Andi Kleen
Date: Sun Apr 29 2007 - 07:11:20 EST

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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.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>

---
arch/i386/kernel/vmlinux.lds.S | 4 ++--
arch/i386/mm/init.c | 27 ++++++++++++++++++++-------
arch/i386/mm/pageattr.c | 6 ++++--
arch/x86_64/kernel/head.S | 1 -
arch/x86_64/kernel/vmlinux.lds.S | 5 +++--
arch/x86_64/mm/init.c | 25 ++++++++++++++++---------
arch/x86_64/mm/pageattr.c | 18 +++++++++++++-----
include/asm-i386/pgtable.h | 2 ++
include/linux/poison.h | 3 ---
9 files changed, 60 insertions(+), 31 deletions(-)

Index: linux/arch/i386/kernel/vmlinux.lds.S
===================================================================
--- linux.orig/arch/i386/kernel/vmlinux.lds.S
+++ linux/arch/i386/kernel/vmlinux.lds.S
@@ -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 */
Index: linux/arch/i386/mm/init.c
===================================================================
--- linux.orig/arch/i386/mm/init.c
+++ linux/arch/i386/mm/init.c
@@ -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);
-
- printk("Write protecting the kernel read-only data: %uk\n",
- (__end_rodata - __start_rodata) >> 10);
+#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);
+ }
+
+ 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, unsigne
__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)
Index: linux/arch/i386/mm/pageattr.c
===================================================================
--- linux.orig/arch/i386/mm/pageattr.c
+++ linux/arch/i386/mm/pageattr.c
@@ -140,9 +140,11 @@ __change_page_attr(struct page *page, pg
kpte = lookup_address(address);
if (!kpte)
return -EINVAL;
+ if (!pte_present(*kpte))
+ return 0;
kpte_page = virt_to_page(kpte);
if (pgprot_val(prot) != pgprot_val(PAGE_KERNEL)) {
- if ((pte_val(*kpte) & _PAGE_PSE) == 0) {
+ if (!pte_huge(*kpte)) {
set_pte_atomic(kpte, mk_pte(page, prot));
} else {
pgprot_t ref_prot;
@@ -158,7 +160,7 @@ __change_page_attr(struct page *page, pg
kpte_page = split;
}
page_private(kpte_page)++;
- } else if ((pte_val(*kpte) & _PAGE_PSE) == 0) {
+ } else if (!pte_huge(*kpte)) {
set_pte_atomic(kpte, mk_pte(page, PAGE_KERNEL));
BUG_ON(page_private(kpte_page) == 0);
page_private(kpte_page)--;
Index: linux/arch/x86_64/kernel/head.S
===================================================================
--- linux.orig/arch/x86_64/kernel/head.S
+++ linux/arch/x86_64/kernel/head.S
@@ -280,7 +280,6 @@ early_idt_ripmsg:

.balign PAGE_SIZE
ENTRY(stext)
-ENTRY(_stext)

#define NEXT_PAGE(name) \
.balign PAGE_SIZE; \
Index: linux/arch/x86_64/kernel/vmlinux.lds.S
===================================================================
--- linux.orig/arch/x86_64/kernel/vmlinux.lds.S
+++ linux/arch/x86_64/kernel/vmlinux.lds.S
@@ -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) {
Index: linux/arch/x86_64/mm/init.c
===================================================================
--- linux.orig/arch/x86_64/mm/init.c
+++ linux/arch/x86_64/mm/init.c
@@ -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, unsigne
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.
Index: linux/arch/x86_64/mm/pageattr.c
===================================================================
--- linux.orig/arch/x86_64/mm/pageattr.c
+++ linux/arch/x86_64/mm/pageattr.c
@@ -126,7 +126,7 @@ __change_page_attr(unsigned long address
struct page *kpte_page;
pgprot_t ref_prot2;
kpte = lookup_address(address);
- if (!kpte) return 0;
+ if (!kpte || !pte_present(*kpte)) return 0;
kpte_page = virt_to_page(((unsigned long)kpte) & PAGE_MASK);
if (pgprot_val(prot) != pgprot_val(ref_prot)) {
if (!pte_huge(*kpte)) {
@@ -179,16 +179,24 @@ __change_page_attr(unsigned long address
int change_page_attr_addr(unsigned long address, int numpages, pgprot_t prot)
{
unsigned long phys_base_pfn = __pa_symbol(__START_KERNEL_map) >> PAGE_SHIFT;
- int err = 0;
+ int err = 0, kernel_map = 0;
int i;

+ if (address >= __START_KERNEL_map
+ && address < __START_KERNEL_map + KERNEL_TEXT_SIZE) {
+ address = (unsigned long)__va(__pa(address));
+ kernel_map = 1;
+ }
+
down_write(&init_mm.mmap_sem);
for (i = 0; i < numpages; i++, address += PAGE_SIZE) {
unsigned long pfn = __pa(address) >> PAGE_SHIFT;

- err = __change_page_attr(address, pfn, prot, PAGE_KERNEL);
- if (err)
- break;
+ if (!kernel_map || pte_present(pfn_pte(0, prot))) {
+ err = __change_page_attr(address, pfn, prot, PAGE_KERNEL);
+ if (err)
+ break;
+ }
/* Handle kernel mapping too which aliases part of the
* lowmem */
if ((pfn >= phys_base_pfn) &&
Index: linux/include/asm-i386/pgtable.h
===================================================================
--- linux.orig/include/asm-i386/pgtable.h
+++ linux/include/asm-i386/pgtable.h
@@ -159,6 +159,7 @@ void paging_init(void);

extern unsigned long long __PAGE_KERNEL, __PAGE_KERNEL_EXEC;
#define __PAGE_KERNEL_RO (__PAGE_KERNEL & ~_PAGE_RW)
+#define __PAGE_KERNEL_RX (__PAGE_KERNEL_EXEC & ~_PAGE_RW)
#define __PAGE_KERNEL_NOCACHE (__PAGE_KERNEL | _PAGE_PCD)
#define __PAGE_KERNEL_LARGE (__PAGE_KERNEL | _PAGE_PSE)
#define __PAGE_KERNEL_LARGE_EXEC (__PAGE_KERNEL_EXEC | _PAGE_PSE)
@@ -166,6 +167,7 @@ extern unsigned long long __PAGE_KERNEL,
#define PAGE_KERNEL __pgprot(__PAGE_KERNEL)
#define PAGE_KERNEL_RO __pgprot(__PAGE_KERNEL_RO)
#define PAGE_KERNEL_EXEC __pgprot(__PAGE_KERNEL_EXEC)
+#define PAGE_KERNEL_RX __pgprot(__PAGE_KERNEL_RX)
#define PAGE_KERNEL_NOCACHE __pgprot(__PAGE_KERNEL_NOCACHE)
#define PAGE_KERNEL_LARGE __pgprot(__PAGE_KERNEL_LARGE)
#define PAGE_KERNEL_LARGE_EXEC __pgprot(__PAGE_KERNEL_LARGE_EXEC)
Index: linux/include/linux/poison.h
===================================================================
--- linux.orig/include/linux/poison.h
+++ linux/include/linux/poison.h
@@ -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
-
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Next message: Andi Kleen: "[PATCH] [23/48] i386: VDSO_PRELINK warning fix"
Previous message: Andi Kleen: "[PATCH] [14/48] x86_64: remove extra smp_processor_id calling"
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Next in thread: Andi Kleen: "[PATCH] [23/48] i386: VDSO_PRELINK warning fix"
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