From: "H.J. Lu" <hjl.tools@gmail.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
linux-doc@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
linux-arch <linux-arch@vger.kernel.org>, X86 ML <x86@kernel.org>,
"H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
"Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Jonathan Corbet <corbet@lwn.net>, Oleg Nesterov <oleg@redhat.com>,
Arnd Bergmann <arnd@arndb.de>,
mike.kravetz@oracle.com
Subject: Re: [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack
Date: Thu, 7 Jun 2018 15:02:44 -0700 [thread overview]
Message-ID: <CAMe9rOr49V8rqRa_KVsw61PWd+crkQvPDgPKtvowazjmsfgWWQ@mail.gmail.com> (raw)
In-Reply-To: <CALCETrXz3WWgZwUXJsDTWvmqKUArQFuMH1xJdSLVKFpTysNWxg@mail.gmail.com>
On Thu, Jun 7, 2018 at 2:01 PM, Andy Lutomirski <luto@kernel.org> wrote:
> On Thu, Jun 7, 2018 at 1:33 PM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>>
>> On Thu, 2018-06-07 at 11:48 -0700, Andy Lutomirski wrote:
>> > On Thu, Jun 7, 2018 at 7:41 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>> > >
>> > > The following operations are provided.
>> > >
>> > > ARCH_CET_STATUS:
>> > > return the current CET status
>> > >
>> > > ARCH_CET_DISABLE:
>> > > disable CET features
>> > >
>> > > ARCH_CET_LOCK:
>> > > lock out CET features
>> > >
>> > > ARCH_CET_EXEC:
>> > > set CET features for exec()
>> > >
>> > > ARCH_CET_ALLOC_SHSTK:
>> > > allocate a new shadow stack
>> > >
>> > > ARCH_CET_PUSH_SHSTK:
>> > > put a return address on shadow stack
>> > >
>> > > ARCH_CET_ALLOC_SHSTK and ARCH_CET_PUSH_SHSTK are intended only for
>> > > the implementation of GLIBC ucontext related APIs.
>> >
>> > Please document exactly what these all do and why. I don't understand
>> > what purpose ARCH_CET_LOCK and ARCH_CET_EXEC serve. CET is opt in for
>> > each ELF program, so I think there should be no need for a magic
>> > override.
>>
>> CET is initially enabled if the loader has CET capability. Then the
>> loader decides if the application can run with CET. If the application
>> cannot run with CET (e.g. a dependent library does not have CET), then
>> the loader turns off CET before passing to the application. When the
>> loader is done, it locks out CET and the feature cannot be turned off
>> anymore until the next exec() call.
>
> Why is the lockout necessary? If user code enables CET and tries to
> run code that doesn't support CET, it will crash. I don't see why we
> need special code in the kernel to prevent a user program from calling
> arch_prctl() and crashing itself. There are already plenty of ways to
> do that :)
On CET enabled machine, not all programs nor shared libraries are
CET enabled. But since ld.so is CET enabled, all programs start
as CET enabled. ld.so will disable CET if a program or any of its shared
libraries aren't CET enabled. ld.so will lock up CET once it is done CET
checking so that CET can't no longer be disabled afterwards.
>> When the next exec() is called, CET
>> feature is turned on/off based on the values set by ARCH_CET_EXEC.
>
> And why do we need ARCH_CET_EXEC?
>
> For background, I really really dislike adding new state that persists
> across exec(). It's nice to get as close to a clean slate as possible
> after exec() so that programs can run in a predictable environment.
> exec() is also a security boundary, and anything a task can do to
> affect itself after exec() needs to have its security implications
> considered very carefully. (As a trivial example, you should not be
> able to use cetcmd ... sudo [malicious options here] to cause sudo to
> run with CET off and then try to exploit it via the malicious options.
>
> If a shutoff is needed for testing, how about teaching ld.so to parse
> LD_CET=no or similar and protect it the same way as LD_PRELOAD is
> protected. Or just do LD_PRELOAD=/lib/libdoesntsupportcet.so.
>
I will take a look.
--
H.J.
next prev parent reply other threads:[~2018-06-07 22:02 UTC|newest]
Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-07 14:37 [PATCH 00/10] Control Flow Enforcement - Part (3) Yu-cheng Yu
2018-06-07 14:37 ` [PATCH 01/10] x86/cet: User-mode shadow stack support Yu-cheng Yu
2018-06-07 16:37 ` Andy Lutomirski
2018-06-07 17:46 ` Yu-cheng Yu
2018-06-07 17:55 ` Dave Hansen
2018-06-07 18:23 ` Andy Lutomirski
2018-06-12 11:56 ` Balbir Singh
2018-06-12 15:03 ` Yu-cheng Yu
2018-06-07 14:37 ` [PATCH 02/10] x86/cet: Introduce WRUSS instruction Yu-cheng Yu
2018-06-07 16:40 ` Andy Lutomirski
2018-06-07 16:51 ` Yu-cheng Yu
2018-06-07 18:41 ` Peter Zijlstra
2018-06-07 20:31 ` Yu-cheng Yu
2018-06-11 8:17 ` Peter Zijlstra
2018-06-11 15:02 ` Yu-cheng Yu
2018-06-14 1:30 ` Balbir Singh
2018-06-14 14:43 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 03/10] x86/cet: Signal handling for shadow stack Yu-cheng Yu
2018-06-07 18:30 ` Andy Lutomirski
2018-06-07 18:58 ` Florian Weimer
2018-06-07 19:51 ` Yu-cheng Yu
2018-06-07 20:07 ` Cyrill Gorcunov
2018-06-07 20:57 ` Andy Lutomirski
2018-06-08 12:07 ` Cyrill Gorcunov
2018-06-07 20:12 ` Yu-cheng Yu
2018-06-07 20:17 ` Dave Hansen
2018-06-07 14:38 ` [PATCH 04/10] x86/cet: Handle thread " Yu-cheng Yu
2018-06-07 18:21 ` Andy Lutomirski
2018-06-07 19:47 ` Florian Weimer
2018-06-07 20:53 ` Andy Lutomirski
2018-06-08 14:53 ` Florian Weimer
2018-06-08 15:01 ` Andy Lutomirski
2018-06-08 15:50 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 05/10] x86/cet: ELF header parsing of Control Flow Enforcement Yu-cheng Yu
2018-06-07 18:38 ` Andy Lutomirski
2018-06-07 20:40 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 06/10] x86/cet: Add arch_prctl functions for shadow stack Yu-cheng Yu
2018-06-07 18:48 ` Andy Lutomirski
2018-06-07 20:30 ` Yu-cheng Yu
2018-06-07 21:01 ` Andy Lutomirski
2018-06-07 22:02 ` H.J. Lu [this message]
2018-06-07 23:01 ` Andy Lutomirski
2018-06-08 4:09 ` H.J. Lu
2018-06-08 4:38 ` Andy Lutomirski
2018-06-08 12:24 ` H.J. Lu
2018-06-08 14:57 ` Andy Lutomirski
2018-06-08 15:52 ` Cyrill Gorcunov
2018-06-08 4:22 ` H.J. Lu
2018-06-08 4:35 ` Andy Lutomirski
2018-06-08 12:17 ` H.J. Lu
2018-06-12 10:03 ` Thomas Gleixner
2018-06-12 11:43 ` H.J. Lu
2018-06-12 16:01 ` Andy Lutomirski
2018-06-12 16:05 ` H.J. Lu
2018-06-12 16:34 ` Andy Lutomirski
2018-06-12 16:51 ` H.J. Lu
2018-06-12 18:59 ` Thomas Gleixner
2018-06-12 19:34 ` H.J. Lu
2018-06-18 22:03 ` Andy Lutomirski
2018-06-19 0:52 ` Kees Cook
2018-06-19 6:40 ` Florian Weimer
2018-06-19 14:50 ` Andy Lutomirski
2018-06-19 16:44 ` Kees Cook
2018-06-19 16:59 ` Yu-cheng Yu
2018-06-19 17:07 ` Kees Cook
2018-06-19 17:20 ` Andy Lutomirski
2018-06-19 20:12 ` Kees Cook
2018-06-19 20:47 ` Andy Lutomirski
2018-06-19 22:38 ` Yu-cheng Yu
2018-06-20 0:50 ` Andy Lutomirski
2018-06-21 23:07 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 07/10] mm: Prevent mprotect from changing " Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 08/10] mm: Prevent mremap of " Yu-cheng Yu
2018-06-07 18:48 ` Andy Lutomirski
2018-06-07 20:18 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 09/10] mm: Prevent madvise from changing " Yu-cheng Yu
2018-06-07 20:54 ` Andy Lutomirski
2018-06-07 21:09 ` Nadav Amit
2018-06-07 21:18 ` Yu-cheng Yu
2018-06-07 14:38 ` [PATCH 10/10] mm: Prevent munmap and remap_file_pages of " Yu-cheng Yu
2018-06-07 18:50 ` Andy Lutomirski
2018-06-07 20:15 ` Yu-cheng Yu
2018-06-12 10:56 ` [PATCH 00/10] Control Flow Enforcement - Part (3) Balbir Singh
2018-06-12 15:03 ` Yu-cheng Yu
2018-06-12 16:00 ` Andy Lutomirski
2018-06-12 16:21 ` Yu-cheng Yu
2018-06-12 16:31 ` Andy Lutomirski
2018-06-12 17:24 ` Yu-cheng Yu
2018-06-12 20:15 ` Yu-cheng Yu
2018-06-14 1:07 ` Balbir Singh
2018-06-14 14:56 ` Yu-cheng Yu
2018-06-17 3:16 ` Balbir Singh
2018-06-18 21:44 ` Andy Lutomirski
2018-06-19 8:52 ` Balbir Singh
2018-06-26 2:46 ` Jann Horn
2018-06-26 14:56 ` Yu-cheng Yu
2018-06-26 5:26 ` Andy Lutomirski
2018-06-26 14:56 ` Yu-cheng Yu
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