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: Fri, 8 Jun 2018 05:24:22 -0700 [thread overview]
Message-ID: <CAMe9rOpLDzWk=xdZqN1QJVnP-c_dti5Fy=C_GqbeQpS_a=0ewA@mail.gmail.com> (raw)
In-Reply-To: <CALCETrWhMmqGWKx-yw55YKHMJwGyLZio5f8Pskh8X69zfQMy7A@mail.gmail.com>
On Thu, Jun 7, 2018 at 9:38 PM, Andy Lutomirski <luto@kernel.org> wrote:
> On Thu, Jun 7, 2018 at 9:10 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>>
>> On Thu, Jun 7, 2018 at 4:01 PM, Andy Lutomirski <luto@kernel.org> wrote:
>> > On Thu, Jun 7, 2018 at 3:02 PM H.J. Lu <hjl.tools@gmail.com> wrote:
>> >>
>> >> 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.
>> >
>> > Yeah, I got that. No one has explained *why*.
>>
>> It is to prevent malicious code from disabling CET.
>>
>
> By the time malicious code issue its own syscalls, you've already lost
> the battle. I could probably be convinced that a lock-CET-on feature
> that applies *only* to the calling thread and is not inherited by
> clone() is a decent idea, but I'd want to see someone who understands
> the state of the art in exploit design justify it. You're also going
> to need to figure out how to make CRIU work if you allow locking CET
> on.
>
> A priori, I think we should just not provide a lock mechanism.
We need a door for CET. But it is a very bad idea to leave it open
all the time. I don't know much about CRIU, If it is Checkpoint/Restore
In Userspace. Can you free any application with AVX512 on AVX512
machine and restore it on non-AVX512 machine?
>> > (Also, shouldn't the vDSO itself be marked as supporting CET?)
>>
>> No. vDSO is loaded by kernel. vDSO in CET kernel is CET
>> compatible.
>>
>
> I think the vDSO should do its best to act like a real DSO. That
> means that, if the vDSO supports CET, it should advertise support for
> CET using the Linux ABI. Since you're going to require GCC 8 anyway,
> this should be a single line of code in the Makefile.
Sure. A couple lines.
--
H.J.
next prev parent reply other threads:[~2018-06-08 12:24 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
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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CAMe9rOpLDzWk=xdZqN1QJVnP-c_dti5Fy=C_GqbeQpS_a=0ewA@mail.gmail.com' \
--to=hjl.tools@gmail.com \
--cc=arnd@arndb.de \
--cc=corbet@lwn.net \
--cc=dave.hansen@linux.intel.com \
--cc=hpa@zytor.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-doc@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=luto@kernel.org \
--cc=mike.kravetz@oracle.com \
--cc=mingo@redhat.com \
--cc=oleg@redhat.com \
--cc=ravi.v.shankar@intel.com \
--cc=tglx@linutronix.de \
--cc=vedvyas.shanbhogue@intel.com \
--cc=x86@kernel.org \
--cc=yu-cheng.yu@intel.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).