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

[Yinghai Lu]

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)));