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Message-ID: <80b3ed527b208d28ee05fb627bc28d91@eikelenboom.it>
Date: Thu, 05 Nov 2015 10:13:56 +0100
From: Sander Eikelenboom <linux@...elenboom.it>
To: Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Stephen Smalley <sds@...ho.nsa.gov>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
David Vrabel <david.vrabel@...rix.com>,
xen-devel@...ts.xen.org, mingo.kernel.org@...il.com
Subject: Re: [Xen-devel] Linux 4.4 MW: Boot under Xen fails with
CONFIG_DEBUG_WX enabled: RIP: ptdump_walk_pgd_level_core
On 2015-11-05 00:13, Boris Ostrovsky wrote:
> On 11/04/2015 03:02 PM, Sander Eikelenboom wrote:
>> On 2015-11-04 19:47, Stephen Smalley wrote:
>>> On 11/04/2015 01:28 PM, Sander Eikelenboom wrote:
>>>> On 2015-11-04 16:52, Stephen Smalley wrote:
>>>>> On 11/04/2015 06:55 AM, Sander Eikelenboom wrote:
>>>>>> Hi All,
>>>>>>
>>>>>> I just tried to boot with the current linus mergewindow tree under
>>>>>> Xen.
>>>>>> It fails with a kernel panic at boot with the new
>>>>>> "CONFIG_DEBUG_WX"
>>>>>> option enabled.
>>>>>> Disabling it makes the kernel boot fine.
>>>>>>
>>>>>> The splat:
>>>>>> [ 18.424241] Freeing unused kernel memory: 1104K
>>>>>> (ffffffff822fc000 -
>>>>>> ffffffff82410000)
>>>>>> [ 18.430314] Write protecting the kernel read-only data: 18432k
>>>>>> [ 18.441054] Freeing unused kernel memory: 1144K
>>>>>> (ffff880001ae2000 -
>>>>>> ffff880001c00000)
>>>>>> [ 18.447966] Freeing unused kernel memory: 1560K
>>>>>> (ffff88000207a000 -
>>>>>> ffff880002200000)
>>>>>> [ 18.453947] BUG: unable to handle kernel paging request at
>>>>>> ffff88055c883000
>>>>>> [ 18.459943] IP: [<ffffffff8105af8e>]
>>>>>> ptdump_walk_pgd_level_core+0x20e/0x440
>>>>>> [ 18.465847] PGD 2212067 PUD 0
>>>>>> [ 18.471564] Oops: 0000 [#1] SMP
>>>>>> [ 18.477248] Modules linked in:
>>>>>> [ 18.482918] CPU: 2 PID: 1 Comm: swapper/0 Not tainted
>>>>>> 4.3.0-mw-20151104-linus-doflr+ #1
>>>>>> [ 18.488804] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640) ,
>>>>>> BIOS
>>>>>> V1.8B1 09/13/2010
>>>>>> [ 18.494778] task: ffff880059b90000 ti: ffff880059b98000
>>>>>> task.ti:
>>>>>> ffff880059b98000
>>>>>> [ 18.500852] RIP: e030:[<ffffffff8105af8e>] [<ffffffff8105af8e>]
>>>>>> ptdump_walk_pgd_level_core+0x20e/0x440
>>>>>> [ 18.507102] RSP: e02b:ffff880059b9be48 EFLAGS: 00010296
>>>>>> [ 18.513351] RAX: ffff88055c883000 RBX: ffffffff81ae2000 RCX:
>>>>>> ffff880000000000
>>>>>> [ 18.519733] RDX: 0000000000000067 RSI: ffff880059b9be98 RDI:
>>>>>> ffff880000001000
>>>>>> [ 18.526129] RBP: ffff880059b9bf00 R08: 0000000000000000 R09:
>>>>>> 0000000000000000
>>>>>> [ 18.532522] R10: ffff88005fd0e790 R11: 0000000000000001 R12:
>>>>>> ffff880080000000
>>>>>> [ 18.538891] R13: ffffc00000000fff R14: ffff880059b9be98 R15:
>>>>>> 0000000000000000
>>>>>> [ 18.545247] FS: 0000000000000000(0000)
>>>>>> GS:ffff88005f680000(0000)
>>>>>> knlGS:0000000000000000
>>>>>> [ 18.551708] CS: e033 DS: 0000 ES: 0000 CR0: 000000008005003b
>>>>>> [ 18.558153] CR2: ffff88055c883000 CR3: 0000000002211000 CR4:
>>>>>> 0000000000000660
>>>>>> [ 18.564686] Stack:
>>>>>> [ 18.571106] 0000000159b9be50 ffffffff82211000 ffff88055c884000
>>>>>> 0000000000000800
>>>>>> [ 18.577704] 0000800000000000 ffff88055c883000 0000000000000007
>>>>>> ffff88005fd0e790
>>>>>> [ 18.584291] ffff880059b9bed8 ffffffff81156ace 0000000000000001
>>>>>> 0000000000000000
>>>>>> [ 18.590916] Call Trace:
>>>>>> [ 18.597458] [<ffffffff81156ace>] ?
>>>>>> free_reserved_area+0x11e/0x120
>>>>>> [ 18.604180] [<ffffffff8105b1e2>]
>>>>>> ptdump_walk_pgd_level_checkwx+0x12/0x20
>>>>>> [ 18.611014] [<ffffffff810515b9>] mark_rodata_ro+0xe9/0xf0
>>>>>> [ 18.617819] [<ffffffff81ad3380>] ? rest_init+0x80/0x80
>>>>>> [ 18.624512] [<ffffffff81ad3398>] kernel_init+0x18/0xe0
>>>>>> [ 18.631095] [<ffffffff81adadcf>] ret_from_fork+0x3f/0x70
>>>>>> [ 18.637650] [<ffffffff81ad3380>] ? rest_init+0x80/0x80
>>>>>> [ 18.644178] Code: 70 ff ff ff 48 3b 85 58 ff ff ff 0f 84 c0 fe
>>>>>> ff ff
>>>>>> 48 8b 85 68 ff ff ff 48 c1 e0 10 48 c1 f8 10 48 89 45 b0 48 8b 85
>>>>>> 70 ff
>>>>>> ff ff <48> 8b 38 48 85 ff 0f 85 4e ff ff ff b9 02 00 00 00 31 d2
>>>>>> 4c 89
>>>>>> [ 18.658246] RIP [<ffffffff8105af8e>]
>>>>>> ptdump_walk_pgd_level_core+0x20e/0x440
>>>>>> [ 18.665211] RSP <ffff880059b9be48>
>>>>>> [ 18.672073] CR2: ffff88055c883000
>>>>>> [ 18.678852] ---[ end trace d84e34461c40637a ]---
>>>>>> [ 18.685641] Kernel panic - not syncing: Attempted to kill init!
>>>>>> exitcode=0x00000009
>>>>>> [ 18.685641]
>>>>>> [ 18.699520] Kernel Offset: disable
>>>>>>
>>>>>
>>>>> What's your .config? Does cat /sys/kernel/debug/kernel_page_tables
>>>>> produce a similar fault even with CONFIG_DEBUG_WX=n?
>>>>
>>>> .config is attached
>>>>
>>>> Hmm that sysfs file doesn't seem to exist then:
>>>> # cat /sys/kernel/debug/kernel_page_tables
>>>> cat: /sys/kernel/debug/kernel_page_tables: No such file or directory
>>>
>>> Needs CONFIG_X86_PTDUMP=y.
>>> Also assumes you have debugfs mounted there.
>>
>> Recompiled, and the result is that it also blows up:
>>
>
> Can you try this:
>
>
> diff --git a/arch/x86/mm/dump_pagetables.c
> b/arch/x86/mm/dump_pagetables.c
> index 1bf417e..b534216 100644
> --- a/arch/x86/mm/dump_pagetables.c
> +++ b/arch/x86/mm/dump_pagetables.c
> @@ -362,8 +362,13 @@ static void ptdump_walk_pgd_level_core(struct
> seq_file *m, pgd_t *pgd,
> bool checkwx)
> {
> #ifdef CONFIG_X86_64
> +/* ffff800000000000 - ffff87ffffffffff is reserved for hypervisor */
> +#define is_hypervisor_range(idx) (paravirt_enabled() && \
> + ((idx >= pgd_index(__PAGE_OFFSET) - 16) && \
> + (idx < pgd_index(__PAGE_OFFSET))))
> pgd_t *start = (pgd_t *) &init_level4_pgt;
> #else
> +#define is_hypervisor_range(idx) 0
> pgd_t *start = swapper_pg_dir;
> #endif
> pgprotval_t prot;
> @@ -381,7 +386,7 @@ static void ptdump_walk_pgd_level_core(struct
> seq_file *m, pgd_t *pgd,
>
> for (i = 0; i < PTRS_PER_PGD; i++) {
> st.current_address = normalize_addr(i * PGD_LEVEL_MULT);
> - if (!pgd_none(*start)) {
> + if (!pgd_none(*start) && !is_hypervisor_range(i)) {
> if (pgd_large(*start) || !pgd_present(*start)) {
> prot = pgd_flags(*start);
> note_page(m, &st, __pgprot(prot), 1);
Hi Boris,
Thank for your patch !
It makes "cat /sys/kernel/debug/kernel_page_tables" work and
prevents a kernel with CONFIG_DEBUG_WX=y from crashing at boot.
It now does give a warning about an insecure W+X mapping, so
CONFIG_DEBUG_WX=y
seems to be working. No idea how to interpret it though (and if it's a
legit
warning).
--
Sander
[ 19.034706] Freeing unused kernel memory: 1104K (ffffffff822fc000 -
ffffffff82410000)
[ 19.041339] Write protecting the kernel read-only data: 18432k
[ 19.052596] Freeing unused kernel memory: 1144K (ffff880001ae2000 -
ffff880001c00000)
[ 19.060285] Freeing unused kernel memory: 1560K (ffff88000207a000 -
ffff880002200000)
[ 19.067079] ------------[ cut here ]------------
[ 19.073931] WARNING: CPU: 5 PID: 1 at
arch/x86/mm/dump_pagetables.c:225 note_page+0x619/0x7e0()
[ 19.081039] x86/mm: Found insecure W+X mapping at address
ffff880000000000/0xffff880000000000
[ 19.088293] Modules linked in:
[ 19.095477] CPU: 5 PID: 1 Comm: swapper/0 Not tainted
4.3.0-mw-20151104-linus-doflr-withdebugwx-noptdump-ptdumppatch+ #1
[ 19.102971] Hardware name: MSI MS-7640/890FXA-GD70 (MS-7640) , BIOS
V1.8B1 09/13/2010
[ 19.110594] ffffffff81f381d3 ffff880059b9bd60 ffffffff81428992
ffff880059b9bda8
[ 19.118239] ffff880059b9bd98 ffffffff810ca7ec ffff8800025d8010
0000000000000004
[ 19.125870] 0010000000000067 ffff880059b9be98 0000000000000000
ffff880059b9bdf8
[ 19.133526] Call Trace:
[ 19.141212] [<ffffffff81428992>] dump_stack+0x44/0x62
[ 19.148983] [<ffffffff810ca7ec>] warn_slowpath_common+0x7c/0xb0
[ 19.156877] [<ffffffff810ca867>] warn_slowpath_fmt+0x47/0x50
[ 19.164813] [<ffffffff8105abb9>] note_page+0x619/0x7e0
[ 19.172656] [<ffffffff8105b135>]
ptdump_walk_pgd_level_core+0x3b5/0x450
[ 19.180583] [<ffffffff8105b1f2>]
ptdump_walk_pgd_level_checkwx+0x12/0x20
[ 19.188427] [<ffffffff810515b9>] mark_rodata_ro+0xe9/0xf0
[ 19.196221] [<ffffffff81ad2f70>] ? rest_init+0x80/0x80
[ 19.204012] [<ffffffff81ad2f88>] kernel_init+0x18/0xe0
[ 19.211732] [<ffffffff81ada98f>] ret_from_fork+0x3f/0x70
[ 19.219467] [<ffffffff81ad2f70>] ? rest_init+0x80/0x80
[ 19.227145] ---[ end trace 5fc0f4297b911570 ]---
[ 19.244382] x86/mm: Checked W+X mappings: FAILED, 4602 W+X pages
found.
--
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