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From: Jann Horn <jannh@google.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
	Nadav Amit <nadav.amit@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Brian Gerst <brgerst@gmail.com>,
	"kernel-hardening@lists.openwall.com" 
	<kernel-hardening@lists.openwall.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jann@thejh.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support
Date: Tue, 21 Jun 2016 09:30:31 +0200	[thread overview]
Message-ID: <CAG48ez3WGu+03HDBA5daSV+zXGoR+iFHHYxZav0o6JCM9-EPMg@mail.gmail.com> (raw)
In-Reply-To: <f7855f9eae0a27f5a03db1291f46fea1cc0a2a3f.1466466093.git.luto@kernel.org>

On Tue, Jun 21, 2016 at 1:43 AM, Andy Lutomirski <luto@kernel.org> wrote:
> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with
> vmalloc_node.
[...]
>  static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>                                                   int node)
>  {
> +#ifdef CONFIG_VMAP_STACK
> +       struct thread_info *ti = __vmalloc_node_range(
> +               THREAD_SIZE, THREAD_SIZE, VMALLOC_START, VMALLOC_END,
> +               THREADINFO_GFP | __GFP_HIGHMEM, PAGE_KERNEL,
> +               0, node, __builtin_return_address(0));
> +

After spender gave some hints on IRC about the guard pages not working
reliably, I decided to have a closer look at this. As far as I can
tell, the idea is that __vmalloc_node_range() automatically adds guard
pages unless the VM_NO_GUARD flag is specified. However, those guard
pages are *behind* allocations, not in front of them, while a stack
guard primarily needs to be in front of the allocation. This wouldn't
matter if all allocations in the vmalloc area had guard pages behind
them, but if someone first does some data allocation with VM_NO_GUARD
and then a stack allocation directly behind that, there won't be a
guard between the data allocation and the stack allocation.

(I might be wrong though; this is only from looking at the code, not
from testing it.)

WARNING: multiple messages have this Message-ID (diff)
From: Jann Horn <jannh@google.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org, linux-kernel@vger.kernel.org,
	linux-arch@vger.kernel.org, Borislav Petkov <bp@alien8.de>,
	Nadav Amit <nadav.amit@gmail.com>,
	Kees Cook <keescook@chromium.org>,
	Brian Gerst <brgerst@gmail.com>,
	"kernel-hardening@lists.openwall.com"
	<kernel-hardening@lists.openwall.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>, Jann Horn <jann@thejh.net>,
	Heiko Carstens <heiko.carstens@de.ibm.com>
Subject: [kernel-hardening] Re: [PATCH v3 06/13] fork: Add generic vmalloced stack support
Date: Tue, 21 Jun 2016 09:30:31 +0200	[thread overview]
Message-ID: <CAG48ez3WGu+03HDBA5daSV+zXGoR+iFHHYxZav0o6JCM9-EPMg@mail.gmail.com> (raw)
In-Reply-To: <f7855f9eae0a27f5a03db1291f46fea1cc0a2a3f.1466466093.git.luto@kernel.org>

On Tue, Jun 21, 2016 at 1:43 AM, Andy Lutomirski <luto@kernel.org> wrote:
> If CONFIG_VMAP_STACK is selected, kernel stacks are allocated with
> vmalloc_node.
[...]
>  static struct thread_info *alloc_thread_info_node(struct task_struct *tsk,
>                                                   int node)
>  {
> +#ifdef CONFIG_VMAP_STACK
> +       struct thread_info *ti = __vmalloc_node_range(
> +               THREAD_SIZE, THREAD_SIZE, VMALLOC_START, VMALLOC_END,
> +               THREADINFO_GFP | __GFP_HIGHMEM, PAGE_KERNEL,
> +               0, node, __builtin_return_address(0));
> +

After spender gave some hints on IRC about the guard pages not working
reliably, I decided to have a closer look at this. As far as I can
tell, the idea is that __vmalloc_node_range() automatically adds guard
pages unless the VM_NO_GUARD flag is specified. However, those guard
pages are *behind* allocations, not in front of them, while a stack
guard primarily needs to be in front of the allocation. This wouldn't
matter if all allocations in the vmalloc area had guard pages behind
them, but if someone first does some data allocation with VM_NO_GUARD
and then a stack allocation directly behind that, there won't be a
guard between the data allocation and the stack allocation.

(I might be wrong though; this is only from looking at the code, not
from testing it.)

  reply	other threads:[~2016-06-21 10:04 UTC|newest]

Thread overview: 269+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-20 23:43 [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Andy Lutomirski
2016-06-20 23:43 ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43 ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 01/13] x86/mm/hotplug: Don't remove PGD entries in remove_pagetable() Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 02/13] x86/cpa: In populate_pgd, don't set the pgd entry until it's populated Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 03/13] x86/mm: Remove kernel_unmap_pages_in_pgd() and efi_cleanup_page_tables() Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:53   ` Matt Fleming
2016-06-21  9:53     ` [kernel-hardening] " Matt Fleming
2016-06-21  9:53     ` Matt Fleming
2016-06-20 23:43 ` [PATCH v3 04/13] mm: Track NR_KERNEL_STACK in KiB instead of number of stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:46   ` Vladimir Davydov
2016-06-21  9:46     ` [kernel-hardening] " Vladimir Davydov
2016-06-21  9:46     ` Vladimir Davydov
2016-06-21  9:46     ` Vladimir Davydov
2016-06-22  7:35   ` Michal Hocko
2016-06-22  7:35     ` [kernel-hardening] " Michal Hocko
2016-06-22  7:35     ` Michal Hocko
2016-06-22  7:35     ` Michal Hocko
2016-06-20 23:43 ` [PATCH v3 05/13] mm: Fix memcg stack accounting for sub-page stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  9:54   ` Vladimir Davydov
2016-06-21  9:54     ` [kernel-hardening] " Vladimir Davydov
2016-06-21  9:54     ` Vladimir Davydov
2016-06-21  9:54     ` Vladimir Davydov
2016-06-22  7:38   ` Michal Hocko
2016-06-22  7:38     ` [kernel-hardening] " Michal Hocko
2016-06-22  7:38     ` Michal Hocko
2016-06-22  7:38     ` Michal Hocko
2016-06-20 23:43 ` [PATCH v3 06/13] fork: Add generic vmalloced stack support Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  7:30   ` Jann Horn [this message]
2016-06-21  7:30     ` [kernel-hardening] " Jann Horn
2016-06-21  7:30     ` Jann Horn
2016-06-21 16:59     ` Andy Lutomirski
2016-06-21 16:59       ` [kernel-hardening] " Andy Lutomirski
2016-06-21 16:59       ` Andy Lutomirski
2016-06-21 17:13       ` Kees Cook
2016-06-21 17:13         ` [kernel-hardening] " Kees Cook
2016-06-21 17:13         ` Kees Cook
2016-06-21 17:28         ` Andy Lutomirski
2016-06-21 17:28           ` [kernel-hardening] " Andy Lutomirski
2016-06-21 17:28           ` Andy Lutomirski
2016-06-21 18:32         ` [kernel-hardening] " Rik van Riel
2016-06-21 18:32           ` Rik van Riel
2016-06-21 19:44           ` [kernel-hardening] " Arnd Bergmann
2016-06-21 19:44             ` Arnd Bergmann
2016-06-21 19:43             ` [kernel-hardening] " Andy Lutomirski
2016-06-21 19:43               ` Andy Lutomirski
2016-06-21 19:43               ` Andy Lutomirski
2016-07-11 17:00           ` [kernel-hardening] " Andrey Ryabinin
2016-06-20 23:43 ` [PATCH v3 07/13] x86/die: Don't try to recover from an OOPS on a non-default stack Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 08/13] x86/dumpstack: When OOPSing, rewind the stack before do_exit Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 09/13] x86/dumpstack: When dumping stack bytes due to OOPS, start with regs->sp Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 10/13] x86/dumpstack: Try harder to get a call trace on stack overflow Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 11/13] x86/dumpstack/64: Handle faults when printing the "Stack:" part of an OOPS Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 12/13] x86/mm/64: Enable vmapped stacks Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-20 23:43 ` [PATCH v3 13/13] x86/mm: Improve stack-overflow #PF handling Andy Lutomirski
2016-06-20 23:43   ` [kernel-hardening] " Andy Lutomirski
2016-06-20 23:43   ` Andy Lutomirski
2016-06-21  4:01 ` [PATCH v3 00/13] Virtually mapped stacks with guard pages (x86, core) Linus Torvalds
2016-06-21  4:01   ` [kernel-hardening] " Linus Torvalds
2016-06-21  4:01   ` Linus Torvalds
2016-06-21 16:45   ` Andy Lutomirski
2016-06-21 16:45     ` [kernel-hardening] " Andy Lutomirski
2016-06-21 16:45     ` Andy Lutomirski
2016-06-21 17:16     ` Linus Torvalds
2016-06-21 17:16       ` [kernel-hardening] " Linus Torvalds
2016-06-21 17:16       ` Linus Torvalds
2016-06-21 17:27       ` Andy Lutomirski
2016-06-21 17:27         ` [kernel-hardening] " Andy Lutomirski
2016-06-21 17:27         ` Andy Lutomirski
2016-06-21 18:12         ` Kees Cook
2016-06-21 18:12           ` [kernel-hardening] " Kees Cook
2016-06-21 18:12           ` Kees Cook
2016-06-21 18:19           ` [kernel-hardening] " Rik van Riel
2016-06-21 18:19             ` Rik van Riel
2016-06-23  1:22   ` Andy Lutomirski
2016-06-23  1:22     ` [kernel-hardening] " Andy Lutomirski
2016-06-23  1:22     ` Andy Lutomirski
2016-06-23  6:02     ` Linus Torvalds
2016-06-23  6:02       ` [kernel-hardening] " Linus Torvalds
2016-06-23  6:02       ` Linus Torvalds
2016-06-23 14:31       ` Oleg Nesterov
2016-06-23 14:31         ` [kernel-hardening] " Oleg Nesterov
2016-06-23 14:31         ` Oleg Nesterov
2016-06-23 16:30         ` Linus Torvalds
2016-06-23 16:30           ` [kernel-hardening] " Linus Torvalds
2016-06-23 16:30           ` Linus Torvalds
2016-06-23 16:41           ` Andy Lutomirski
2016-06-23 16:41             ` [kernel-hardening] " Andy Lutomirski
2016-06-23 16:41             ` Andy Lutomirski
2016-06-23 17:10             ` Oleg Nesterov
2016-06-23 17:10               ` [kernel-hardening] " Oleg Nesterov
2016-06-23 17:10               ` Oleg Nesterov
2016-09-06 16:19             ` Jann Horn
2016-09-06 16:19               ` [kernel-hardening] " Jann Horn
2016-09-06 16:19               ` Jann Horn
2016-09-06 16:40               ` Andy Lutomirski
2016-09-06 16:40                 ` [kernel-hardening] " Andy Lutomirski
2016-09-06 16:40                 ` Andy Lutomirski
2016-06-23 17:03           ` Oleg Nesterov
2016-06-23 17:03             ` [kernel-hardening] " Oleg Nesterov
2016-06-23 17:03             ` Oleg Nesterov
2016-06-23 17:44             ` Linus Torvalds
2016-06-23 17:44               ` [kernel-hardening] " Linus Torvalds
2016-06-23 17:44               ` Linus Torvalds
2016-06-23 17:52               ` Linus Torvalds
2016-06-23 17:52                 ` [kernel-hardening] " Linus Torvalds
2016-06-23 17:52                 ` Linus Torvalds
2016-06-23 18:00                 ` Kees Cook
2016-06-23 18:00                   ` [kernel-hardening] " Kees Cook
2016-06-23 18:00                   ` Kees Cook
2016-06-23 18:54                   ` Peter Zijlstra
2016-06-23 18:54                     ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:54                     ` Peter Zijlstra
2016-06-23 18:12                 ` Oleg Nesterov
2016-06-23 18:12                   ` [kernel-hardening] " Oleg Nesterov
2016-06-23 18:12                   ` Oleg Nesterov
2016-06-23 18:55                   ` Peter Zijlstra
2016-06-23 18:55                     ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:55                     ` Peter Zijlstra
2016-06-23 18:46                 ` Linus Torvalds
2016-06-23 18:46                   ` [kernel-hardening] " Linus Torvalds
2016-06-23 18:46                   ` Linus Torvalds
2016-06-23 19:08                   ` Andy Lutomirski
2016-06-23 19:08                     ` [kernel-hardening] " Andy Lutomirski
2016-06-23 19:08                     ` Andy Lutomirski
2016-06-23 18:53                 ` Peter Zijlstra
2016-06-23 18:53                   ` [kernel-hardening] " Peter Zijlstra
2016-06-23 18:53                   ` Peter Zijlstra
2016-06-23 19:09                   ` Andy Lutomirski
2016-06-23 19:09                     ` [kernel-hardening] " Andy Lutomirski
2016-06-23 19:09                     ` Andy Lutomirski
2016-06-23 19:13                     ` Peter Zijlstra
2016-06-23 19:13                       ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:13                       ` Peter Zijlstra
2016-06-23 19:17                   ` Linus Torvalds
2016-06-23 19:17                     ` [kernel-hardening] " Linus Torvalds
2016-06-23 19:17                     ` Linus Torvalds
2016-06-24  6:17                     ` Linus Torvalds
2016-06-24  6:17                       ` [kernel-hardening] " Linus Torvalds
2016-06-24  6:17                       ` Linus Torvalds
2016-06-24 12:25                       ` Brian Gerst
2016-06-24 12:25                         ` [kernel-hardening] " Brian Gerst
2016-06-24 12:25                         ` Brian Gerst
2016-06-24 17:21                         ` Linus Torvalds
2016-06-24 17:21                           ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:21                           ` Linus Torvalds
2016-06-24 17:40                           ` Linus Torvalds
2016-06-24 17:40                             ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:40                             ` Linus Torvalds
2016-06-24 17:47                             ` Andy Lutomirski
2016-06-24 17:47                               ` [kernel-hardening] " Andy Lutomirski
2016-06-24 17:47                               ` Andy Lutomirski
2016-06-24 17:56                               ` Linus Torvalds
2016-06-24 17:56                                 ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:56                                 ` Linus Torvalds
2016-06-24 18:36                                 ` Andy Lutomirski
2016-06-24 18:36                                   ` [kernel-hardening] " Andy Lutomirski
2016-06-24 18:36                                   ` Andy Lutomirski
2016-06-24 17:51                             ` Linus Torvalds
2016-06-24 17:51                               ` [kernel-hardening] " Linus Torvalds
2016-06-24 17:51                               ` Linus Torvalds
2016-06-24 18:11                               ` Linus Torvalds
2016-06-24 18:11                                 ` [kernel-hardening] " Linus Torvalds
2016-06-24 18:11                                 ` Linus Torvalds
2016-06-24 20:25                                 ` Josh Poimboeuf
2016-06-24 20:25                                   ` [kernel-hardening] " Josh Poimboeuf
2016-06-24 20:25                                   ` Josh Poimboeuf
2016-06-24 20:51                                   ` Josh Poimboeuf
2016-06-24 20:51                                     ` [kernel-hardening] " Josh Poimboeuf
2016-06-24 20:51                                     ` Josh Poimboeuf
2016-06-24 20:53                                     ` Andy Lutomirski
2016-06-24 20:53                                       ` [kernel-hardening] " Andy Lutomirski
2016-06-24 20:53                                       ` Andy Lutomirski
2016-06-24 21:06                                     ` Linus Torvalds
2016-06-24 21:06                                       ` [kernel-hardening] " Linus Torvalds
2016-06-24 21:06                                       ` Linus Torvalds
2016-06-24 21:25                                       ` Andy Lutomirski
2016-06-24 21:25                                         ` [kernel-hardening] " Andy Lutomirski
2016-06-24 21:25                                         ` Andy Lutomirski
2016-06-24 21:32                                         ` Linus Torvalds
2016-06-24 21:32                                           ` [kernel-hardening] " Linus Torvalds
2016-06-24 21:32                                           ` Linus Torvalds
2016-06-24 21:34                                           ` Andy Lutomirski
2016-06-24 21:34                                             ` [kernel-hardening] " Andy Lutomirski
2016-06-24 21:34                                             ` Andy Lutomirski
2016-06-25  2:41                                             ` Linus Torvalds
2016-06-25  2:41                                               ` [kernel-hardening] " Linus Torvalds
2016-06-25  2:41                                               ` Linus Torvalds
2016-06-25 23:19                                               ` Andy Lutomirski
2016-06-25 23:19                                                 ` [kernel-hardening] " Andy Lutomirski
2016-06-25 23:19                                                 ` Andy Lutomirski
2016-06-25 23:30                                                 ` Andy Lutomirski
2016-06-25 23:30                                                   ` [kernel-hardening] " Andy Lutomirski
2016-06-25 23:30                                                   ` Andy Lutomirski
2016-06-26  1:23                                                   ` Linus Torvalds
2016-06-26  1:23                                                     ` [kernel-hardening] " Linus Torvalds
2016-06-26  1:23                                                     ` Linus Torvalds
2016-06-23 18:52               ` Oleg Nesterov
2016-06-23 18:52                 ` [kernel-hardening] " Oleg Nesterov
2016-06-23 18:52                 ` Oleg Nesterov
2016-06-24 14:05                 ` Michal Hocko
2016-06-24 14:05                   ` [kernel-hardening] " Michal Hocko
2016-06-24 14:05                   ` Michal Hocko
2016-06-24 15:06                   ` Michal Hocko
2016-06-24 15:06                     ` [kernel-hardening] " Michal Hocko
2016-06-24 15:06                     ` Michal Hocko
2016-06-24 15:06                     ` Michal Hocko
2016-06-24 20:22                     ` Oleg Nesterov
2016-06-24 20:22                       ` [kernel-hardening] " Oleg Nesterov
2016-06-24 20:22                       ` Oleg Nesterov
2016-06-27 10:36                       ` Michal Hocko
2016-06-27 10:36                         ` [kernel-hardening] " Michal Hocko
2016-06-27 10:36                         ` Michal Hocko
2016-06-23 19:11         ` Peter Zijlstra
2016-06-23 19:11           ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:11           ` Peter Zijlstra
2016-06-23 19:34           ` Linus Torvalds
2016-06-23 19:34             ` [kernel-hardening] " Linus Torvalds
2016-06-23 19:34             ` Linus Torvalds
2016-06-23 19:46             ` Peter Zijlstra
2016-06-23 19:46               ` [kernel-hardening] " Peter Zijlstra
2016-06-23 19:46               ` Peter Zijlstra
2016-06-21  9:24 ` Arnd Bergmann
2016-06-21  9:24   ` [kernel-hardening] " Arnd Bergmann
2016-06-21  9:24   ` Arnd Bergmann
2016-06-21 17:16   ` Kees Cook
2016-06-21 17:16     ` [kernel-hardening] " Kees Cook
2016-06-21 17:16     ` Kees Cook
2016-06-21 18:02     ` [kernel-hardening] " Rik van Riel
2016-06-21 18:02       ` Rik van Riel
2016-06-21 18:05       ` [kernel-hardening] " Andy Lutomirski
2016-06-21 18:05         ` Andy Lutomirski
2016-06-21 18:05         ` Andy Lutomirski
2016-06-21 19:47     ` Arnd Bergmann
2016-06-21 19:47       ` [kernel-hardening] " Arnd Bergmann
2016-06-21 19:47       ` Arnd Bergmann
2016-06-21 19:47       ` Andy Lutomirski
2016-06-21 19:47         ` [kernel-hardening] " Andy Lutomirski
2016-06-21 19:47         ` Andy Lutomirski
2016-06-21 20:18         ` Kees Cook
2016-06-21 20:18           ` [kernel-hardening] " Kees Cook
2016-06-21 20:18           ` Kees Cook

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