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.)
next prev parent 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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