Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

From: Yinghai Lu
Date: Fri Nov 14 2014 - 21:29:52 EST


On Fri, Nov 14, 2014 at 5:29 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:
> On Fri, Nov 14, 2014 at 12:45 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
>> v2:
>> - added call to free_init_pages(), as suggested by tglx

> something is wrong:
>
> [ 7.842479] Freeing unused kernel memory: 3844K (ffffffff82e52000 -
> ffffffff83213000)
> [ 7.843305] Write protecting the kernel read-only data: 28672k

....
should use attached one instead.

1. should use _brk_end instead of &end, as we only use partial of
brk.
2. [_brk_end, pm_end) page range is already converted. aka
is not wasted.

---
arch/x86/mm/init_64.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/mm/init_64.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/init_64.c
+++ linux-2.6/arch/x86/mm/init_64.c
@@ -1124,7 +1124,8 @@ void mark_rodata_ro(void)
unsigned long end = (unsigned long) &__end_rodata_hpage_align;
unsigned long text_end = PFN_ALIGN(&__stop___ex_table);
unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
- unsigned long all_end = PFN_ALIGN(&_end);
+ unsigned long all_end = PFN_ALIGN(_brk_end);
+ unsigned long pmd_end = roundup(all_end, PMD_SIZE);

printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
(end - start) >> 10);
@@ -1136,7 +1137,7 @@ void mark_rodata_ro(void)
* The rodata/data/bss/brk section (but not the kernel text!)
* should also be not-executable.
*/
- set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
+ set_memory_nx(rodata_start, (pmd_end - rodata_start) >> PAGE_SHIFT);

rodata_test();

@@ -1148,6 +1149,7 @@ void mark_rodata_ro(void)
set_memory_ro(start, (end-start) >> PAGE_SHIFT);
#endif

+ /* all_end to pmd_end is handled via free_all_bootmem() */
free_init_pages("unused kernel",
(unsigned long) __va(__pa_symbol(text_end)),
(unsigned long) __va(__pa_symbol(rodata_start)));
1. should use _brk_end instead of &end, as we only use partial of
brk.
2. [_brk_end, pm_end) page range is already converted. aka
is not wasted.

---
arch/x86/mm/init_64.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

Index: linux-2.6/arch/x86/mm/init_64.c
===================================================================
--- linux-2.6.orig/arch/x86/mm/init_64.c
+++ linux-2.6/arch/x86/mm/init_64.c
@@ -1124,7 +1124,8 @@ void mark_rodata_ro(void)
unsigned long end = (unsigned long) &__end_rodata_hpage_align;
unsigned long text_end = PFN_ALIGN(&__stop___ex_table);
unsigned long rodata_end = PFN_ALIGN(&__end_rodata);
- unsigned long all_end = PFN_ALIGN(&_end);
+ unsigned long all_end = PFN_ALIGN(_brk_end);
+ unsigned long pmd_end = roundup(all_end, PMD_SIZE);

printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
(end - start) >> 10);
@@ -1136,7 +1137,7 @@ void mark_rodata_ro(void)
* The rodata/data/bss/brk section (but not the kernel text!)
* should also be not-executable.
*/
- set_memory_nx(rodata_start, (all_end - rodata_start) >> PAGE_SHIFT);
+ set_memory_nx(rodata_start, (pmd_end - rodata_start) >> PAGE_SHIFT);

rodata_test();

@@ -1148,6 +1149,7 @@ void mark_rodata_ro(void)
set_memory_ro(start, (end-start) >> PAGE_SHIFT);
#endif

+ /* all_end to pmd_end is handled via free_all_bootmem() */
free_init_pages("unused kernel",
(unsigned long) __va(__pa_symbol(text_end)),
(unsigned long) __va(__pa_symbol(rodata_start)));