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Message-ID: <CAGXu5jKVbEDCyu7p0_9CHKm81j+DCqr-tToYq_KAPBieNkkwmw@mail.gmail.com>
Date: Fri, 14 Nov 2014 19:06:15 -0800
From: Kees Cook <keescook@...omium.org>
To: Yinghai Lu <yinghai@...nel.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:
>> When setting up permissions on kernel memory at boot, the end of the
>> PMD that was split from bss remained executable. It should be NX like
>> the rest. This performs a PMD alignment instead of a PAGE alignment to
>> get the correct span of memory, and should be freed.
>>
>> Before:
>> ---[ High Kernel Mapping ]---
>> ...
>> 0xffffffff8202d000-0xffffffff82200000 1868K RW GLB NX pte
>> 0xffffffff82200000-0xffffffff82c00000 10M RW PSE GLB NX pmd
>> 0xffffffff82c00000-0xffffffff82df5000 2004K RW GLB NX pte
>> 0xffffffff82df5000-0xffffffff82e00000 44K RW GLB x pte
>> 0xffffffff82e00000-0xffffffffc0000000 978M pmd
>>
>> After:
>> ---[ High Kernel Mapping ]---
>> ...
>> 0xffffffff8202d000-0xffffffff82200000 1868K RW GLB NX pte
>> 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
>>
>> Signed-off-by: Kees Cook <keescook@...omium.org>
>> ---
>> v2:
>> - added call to free_init_pages(), as suggested by tglx
>> ---
>> arch/x86/mm/init_64.c | 4 +++-
>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/mm/init_64.c b/arch/x86/mm/init_64.c
>> index 4cb8763868fc..0d498c922668 100644
>> --- a/arch/x86/mm/init_64.c
>> +++ b/arch/x86/mm/init_64.c
>> @@ -1124,6 +1124,7 @@ void mark_rodata_ro(void)
>> 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 pmd_end = roundup(all_end, PMD_SIZE);
>>
>> printk(KERN_INFO "Write protecting the kernel read-only data: %luk\n",
>> (end - start) >> 10);
>> @@ -1135,7 +1136,7 @@ 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();
>>
>> @@ -1147,6 +1148,7 @@ void mark_rodata_ro(void)
>> set_memory_ro(start, (end-start) >> PAGE_SHIFT);
>> #endif
>>
>> + free_init_pages("unused kernel", all_end, pmd_end);
>> free_init_pages("unused kernel",
>> (unsigned long) __va(__pa_symbol(text_end)),
>> (unsigned long) __va(__pa_symbol(rodata_start)));
>
> something is wrong:
>
> [ 7.842479] Freeing unused kernel memory: 3844K (ffffffff82e52000 -
> ffffffff83213000)
> [ 7.843305] Write protecting the kernel read-only data: 28672k
> [ 7.844433] BUG: Bad page state in process swapper/0 pfn:043c0
> [ 7.845093] page:ffffea000010f000 count:0 mapcount:-127 mapping:
> (null) index:0x2
> [ 7.846388] flags: 0x10000000000000()
> [ 7.846871] page dumped because: nonzero mapcount
> [ 7.847343] Modules linked in:
> [ 7.847719] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
> 3.18.0-rc4-yh-01896-g40204c8-dirty #23
> [ 7.848809] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
> BIOS rel-1.7.5-0-ge51488c-20140602_164612-nilsson.home.kraxel.org
> 04/01/2014
> [ 7.850014] ffffffff828300ca ffff880078babd68 ffffffff81ff47d0
> 0000000000000001
> [ 7.850857] ffffea000010f000 ffff880078babd98 ffffffff8118c2bd
> 00000000001d4cc0
> [ 7.851791] ffffea000010f000 ffffea000010f000 0000000000000000
> ffff880078babdf8
> [ 7.852700] Call Trace:
> [ 7.852991] [<ffffffff81ff47d0>] dump_stack+0x45/0x57
> [ 7.853494] [<ffffffff8118c2bd>] bad_page+0xfd/0x130
> [ 7.854130] [<ffffffff8118c42c>] free_pages_prepare+0x13c/0x1c0
> [ 7.854808] [<ffffffff8118c64d>] ? adjust_managed_page_count+0x5d/0x70
> [ 7.855575] [<ffffffff8118f285>] free_hot_cold_page+0x35/0x180
> [ 7.856326] [<ffffffff8118f3e3>] __free_pages+0x13/0x40
> [ 7.856854] [<ffffffff8118f4dd>] free_reserved_area+0xcd/0x140
> [ 7.857442] [<ffffffff81091778>] free_init_pages+0x98/0xb0
> [ 7.858001] [<ffffffff81092085>] mark_rodata_ro+0xb5/0x120
> [ 7.858622] [<ffffffff81fe3240>] ? rest_init+0xc0/0xc0
> [ 7.859174] [<ffffffff81fe325d>] kernel_init+0x1d/0x100
> [ 7.859724] [<ffffffff820066ec>] ret_from_fork+0x7c/0xb0
> [ 7.860279] [<ffffffff81fe3240>] ? rest_init+0xc0/0xc0
> [ 7.860836] Disabling lock debugging due to kernel taint
> [ 7.861432] Freeing unused kernel memory: 376K (ffffffff843a2000 -
> ffffffff84400000)
> [ 7.866118] Freeing unused kernel memory: 1980K (ffff880002011000 -
> ffff880002200000)
> [ 7.870525] Freeing unused kernel memory: 1932K (ffff880002a1d000 -
> ffff880002c00000)
Also, what tree is this? "Freeing %s" went away in
c88442ec45f30d587b38b935a14acde4e217a926 (and should probably be
re-added, which is what I assume has happened.)
>
> [ 0.000000] .text: [0x01000000-0x0200d548]
> [ 0.000000] .rodata: [0x02200000-0x02a1cfff]
> [ 0.000000] .data: [0x02c00000-0x02e50e7f]
> [ 0.000000] .init: [0x02e52000-0x03212fff]
> [ 0.000000] .bss: [0x03221000-0x0437bfff]
> [ 0.000000] .brk: [0x0437c000-0x043a1fff]
And which CONFIG turns on this reporting?
-Kees
--
Kees Cook
Chrome OS Security
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