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

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Date:	Fri, 14 Nov 2014 18:29:45 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Wang Nan <wangnan0@...wei.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

On Fri, Nov 14, 2014 at 5:29 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Fri, Nov 14, 2014 at 12:45 PM, Kees Cook <keescook@...omium.org> 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)));

View attachment "nx_after_end.patch" of type "text/x-patch" (1529 bytes)