[PATCH] x86/xen: suppress hugetlbfs in PV guests

[PATCH] x86/xen: suppress hugetlbfs in PV guests

[Jan Beulich]

Huge pages are not normally available to PV guests. Not suppressing
hugetlbfs use results in an endless loop of page faults when user mode
code tries to access a hugetlbfs mapped area (since the hypervisor
denies such PTEs to be created, but error indications can't be
propagated out of xen_set_pte_at(), just like for various of its
siblings), and - once killed in an oops like this:

kernel BUG at .../fs/hugetlbfs/inode.c:428!
invalid opcode: 0000 [#1] SMP 
Modules linked in: ...
Supported: Yes
CPU: 2 PID: 6088 Comm: hugetlbfs Tainted: G        W         4.4.0-2016-01-20-pv #2
Hardware name: ...
task: ffff8808059205c0 ti: ffff880803c84000 task.ti: ffff880803c84000
RIP: e030:[<ffffffff811c333b>]  [<ffffffff811c333b>] remove_inode_hugepages+0x25b/0x320
RSP: e02b:ffff880803c879a8  EFLAGS: 00010202
RAX: 000000000077a4db RBX: ffffea001acff000 RCX: 0000000078417d38
RDX: 0000000000000000 RSI: 000000007e154fa7 RDI: ffff880805d70960
RBP: 0000000000000960 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: ffff880807486018 R14: 0000000000000000 R15: ffff880803c87af0
FS:  00007f85fa8b8700(0000) GS:ffff88080b640000(0000) knlGS:0000000000000000
CS:  e033 DS: 0000 ES: 0000 CR0: 000000008005003b
CR2: 00007f85fa000000 CR3: 0000000001a0a000 CR4: 0000000000040660
Stack:
 ffff880000000fb0 ffff880803c87a18 ffff880803c87ae8 ffff8808059205c0
 ffff880803c87af0 ffff880803c87ae8 ffff880807486018 0000000000000000
 ffffffff81bf6e60 ffff880807486168 000003ffffffffff 0000000003c87758
Call Trace:
 [<ffffffff811c3415>] hugetlbfs_evict_inode+0x15/0x40
 [<ffffffff81167b3d>] evict+0xbd/0x1b0
 [<ffffffff8116514a>] __dentry_kill+0x19a/0x1f0
 [<ffffffff81165b0e>] dput+0x1fe/0x220
 [<ffffffff81150535>] __fput+0x155/0x200
 [<ffffffff81079fc0>] task_work_run+0x60/0xa0
 [<ffffffff81063510>] do_exit+0x160/0x400
 [<ffffffff810637eb>] do_group_exit+0x3b/0xa0
 [<ffffffff8106e8bd>] get_signal+0x1ed/0x470
 [<ffffffff8100f854>] do_signal+0x14/0x110
 [<ffffffff810030e9>] prepare_exit_to_usermode+0xe9/0xf0
 [<ffffffff814178a5>] retint_user+0x8/0x13

This is CVE-2016-3961 / XSA-174.

Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: stable@vger.kernel.org 
---
 arch/x86/include/asm/hugetlb.h |    1 +
 1 file changed, 1 insertion(+)

--- 4.6-rc4/arch/x86/include/asm/hugetlb.h
+++ 4.6-rc4-xsa174/arch/x86/include/asm/hugetlb.h
@@ -4,6 +4,7 @@
 #include <asm/page.h>
 #include <asm-generic/hugetlb.h>
 
+#define hugepages_supported() cpu_has_pse
 
 static inline int is_hugepage_only_range(struct mm_struct *mm,
 					 unsigned long addr,

[tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[tip-bot for Jan Beulich]

Commit-ID:  103f6112f253017d7062cd74d17f4a514ed4485c
Gitweb:     http://git.kernel.org/tip/103f6112f253017d7062cd74d17f4a514ed4485c
Author:     Jan Beulich <JBeulich@suse.com>
AuthorDate: Thu, 21 Apr 2016 00:27:04 -0600
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 22 Apr 2016 10:05:00 +0200

x86/mm/xen: Suppress hugetlbfs in PV guests

Huge pages are not normally available to PV guests. Not suppressing
hugetlbfs use results in an endless loop of page faults when user mode
code tries to access a hugetlbfs mapped area (since the hypervisor
denies such PTEs to be created, but error indications can't be
propagated out of xen_set_pte_at(), just like for various of its
siblings), and - once killed in an oops like this:

  kernel BUG at .../fs/hugetlbfs/inode.c:428!
  invalid opcode: 0000 [#1] SMP
  ...
  RIP: e030:[<ffffffff811c333b>]  [<ffffffff811c333b>] remove_inode_hugepages+0x25b/0x320
  ...
  Call Trace:
   [<ffffffff811c3415>] hugetlbfs_evict_inode+0x15/0x40
   [<ffffffff81167b3d>] evict+0xbd/0x1b0
   [<ffffffff8116514a>] __dentry_kill+0x19a/0x1f0
   [<ffffffff81165b0e>] dput+0x1fe/0x220
   [<ffffffff81150535>] __fput+0x155/0x200
   [<ffffffff81079fc0>] task_work_run+0x60/0xa0
   [<ffffffff81063510>] do_exit+0x160/0x400
   [<ffffffff810637eb>] do_group_exit+0x3b/0xa0
   [<ffffffff8106e8bd>] get_signal+0x1ed/0x470
   [<ffffffff8100f854>] do_signal+0x14/0x110
   [<ffffffff810030e9>] prepare_exit_to_usermode+0xe9/0xf0
   [<ffffffff814178a5>] retint_user+0x8/0x13

This is CVE-2016-3961 / XSA-174.

Reported-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: David Vrabel <david.vrabel@citrix.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <JGross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: stable@vger.kernel.org
Cc: xen-devel <xen-devel@lists.xenproject.org>
Link: http://lkml.kernel.org/r/57188ED802000078000E431C@prv-mh.provo.novell.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/include/asm/hugetlb.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
index f8a29d2..e6a8613 100644
--- a/arch/x86/include/asm/hugetlb.h
+++ b/arch/x86/include/asm/hugetlb.h
@@ -4,6 +4,7 @@
 #include <asm/page.h>
 #include <asm-generic/hugetlb.h>
 
+#define hugepages_supported() cpu_has_pse
 
 static inline int is_hugepage_only_range(struct mm_struct *mm,
 					 unsigned long addr,

Re: [tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[H. Peter Anvin]

On 04/22/2016 02:47 AM, tip-bot for Jan Beulich wrote:
> Commit-ID:  103f6112f253017d7062cd74d17f4a514ed4485c
> Gitweb:     http://git.kernel.org/tip/103f6112f253017d7062cd74d17f4a514ed4485c
> Author:     Jan Beulich <JBeulich@suse.com>
> AuthorDate: Thu, 21 Apr 2016 00:27:04 -0600
> Committer:  Ingo Molnar <mingo@kernel.org>
> CommitDate: Fri, 22 Apr 2016 10:05:00 +0200
> 
> 
> diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
> index f8a29d2..e6a8613 100644
> --- a/arch/x86/include/asm/hugetlb.h
> +++ b/arch/x86/include/asm/hugetlb.h
> @@ -4,6 +4,7 @@
>  #include <asm/page.h>
>  #include <asm-generic/hugetlb.h>
>  
> +#define hugepages_supported() cpu_has_pse
>  

Please don't use the cpu_has_* macros anymore, they are going away soon.

In this case it should be static_cpu_has(X86_FEATURE_PSE).

	-hpa

Re: [tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[Borislav Petkov]

On Fri, Apr 22, 2016 at 11:03:53AM -0700, H. Peter Anvin wrote:
> Please don't use the cpu_has_* macros anymore, they are going away soon.
> 
> In this case it should be static_cpu_has(X86_FEATURE_PSE).

Ingo fixed this up while merging:

b2eafe890d4a ("Merge branch 'x86/urgent' into x86/asm, to fix semantic conflict")

The cpu_has_* things are gone now in tip! \o/

:-)

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.

Re: [tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[Jan Beulich]

>>> On 22.04.16 at 20:03, <hpa@zytor.com> wrote:
> On 04/22/2016 02:47 AM, tip-bot for Jan Beulich wrote:
>> Commit-ID:  103f6112f253017d7062cd74d17f4a514ed4485c
>> Gitweb:     
> http://git.kernel.org/tip/103f6112f253017d7062cd74d17f4a514ed4485c 
>> Author:     Jan Beulich <JBeulich@suse.com>
>> AuthorDate: Thu, 21 Apr 2016 00:27:04 -0600
>> Committer:  Ingo Molnar <mingo@kernel.org>
>> CommitDate: Fri, 22 Apr 2016 10:05:00 +0200
>> 
>> 
>> diff --git a/arch/x86/include/asm/hugetlb.h b/arch/x86/include/asm/hugetlb.h
>> index f8a29d2..e6a8613 100644
>> --- a/arch/x86/include/asm/hugetlb.h
>> +++ b/arch/x86/include/asm/hugetlb.h
>> @@ -4,6 +4,7 @@
>>  #include <asm/page.h>
>>  #include <asm-generic/hugetlb.h>
>>  
>> +#define hugepages_supported() cpu_has_pse
>>  
> 
> Please don't use the cpu_has_* macros anymore, they are going away soon.
> 
> In this case it should be static_cpu_has(X86_FEATURE_PSE).

I can certainly do that, but this
- will (mildly) harm backportability
- imo should have been requested much earlier (when the patch was
  still under discussion)

Jan

Re: [tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[Thomas Gleixner]

On Mon, 25 Apr 2016, Jan Beulich wrote:
> >>> On 22.04.16 at 20:03, <hpa@zytor.com> wrote:
> >> +#define hugepages_supported() cpu_has_pse
> >>  
> > 
> > Please don't use the cpu_has_* macros anymore, they are going away soon.
> > 
> > In this case it should be static_cpu_has(X86_FEATURE_PSE).
> 
> I can certainly do that, but this
> - will (mildly) harm backportability
> - imo should have been requested much earlier (when the patch was
>   still under discussion)

It's requested now as cpu_has_* is going away. So instead of making silly
arguments you should have sent a delta patch fixing this.

Thanks,

	tglx

Re: [Xen-devel] [tip:x86/asm] x86/mm/xen: Suppress hugetlbfs in PV guests

[David Vrabel]

On 25/04/16 08:52, Thomas Gleixner wrote:
> On Mon, 25 Apr 2016, Jan Beulich wrote:
>>>>> On 22.04.16 at 20:03, <hpa@zytor.com> wrote:
>>>> +#define hugepages_supported() cpu_has_pse
>>>>  
>>>
>>> Please don't use the cpu_has_* macros anymore, they are going away soon.
>>>
>>> In this case it should be static_cpu_has(X86_FEATURE_PSE).
>>
>> I can certainly do that, but this
>> - will (mildly) harm backportability
>> - imo should have been requested much earlier (when the patch was
>>   still under discussion)
> 
> It's requested now as cpu_has_* is going away. So instead of making silly
> arguments you should have sent a delta patch fixing this.

Ingo fixed this up in the x86/asm branch[1] so I assumed this patch
didn't need updating.

David

[1]
https://git.kernel.org/cgit/linux/kernel/git/tip/tip.git/commit/?h=x86/asm&id=b2eafe890d4a09bfa63ab31ff018d7d6bb8cfefc