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

[Yinghai Lu]

On Fri, Nov 14, 2014 at 6:46 PM, Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> On Fri, Nov 14, 2014 at 6:29 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote:

>> 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.
>
> Are you sure? For me, _brk_end isn't far enough:
>
> [    1.475572] all_end: 0xffffffff82df5000
> [    1.476736] _brk_end: 0xffffffff82dd6000

Yes. _brk_end should be small then &_end.

>
>>
>> ---
>>  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)));
>
> This patch produces the same results as my v1 patch:
>
> 0xffffffff8202d000-0xffffffff82200000  1868K     RW       GLB NX pte
> 0xffffffff82200000-0xffffffff82e00000    12M     RW   PSE GLB NX pmd
> 0xffffffff82e00000-0xffffffffc0000000   978M                     pmd
>
> Is this correct? It sounded like tglx wanted the pmd split, like this:
>
> 0xffffffff82200000-0xffffffff82c00000    10M     RW   PSE GLB NX pmd
> 0xffffffff82c00000-0xffffffff82df5000  2004K     RW       GLB NX pte
> 0xffffffff82df5000-0xffffffff82e00000    44K     RW           NX pte
> 0xffffffff82e00000-0xffffffffc0000000   978M                     pmd

Need to remove GLB ?

Yinghai
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