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From: Andy Lutomirski <luto@kernel.org>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: Andrew Lutomirski <luto@kernel.org>,
	bsingharora@gmail.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>, "H. J. Lu" <hjl.tools@gmail.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 00/10] Control Flow Enforcement - Part (3)
Date: Tue, 12 Jun 2018 09:31:26 -0700	[thread overview]
Message-ID: <CALCETrVOyZz72RuoRB=z_EjFTqqctSLfX30GM+MSEVtbcd=PeQ@mail.gmail.com> (raw)
In-Reply-To: <1528820489.9324.14.camel@2b52.sc.intel.com>

On Tue, Jun 12, 2018 at 9:24 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
>
> On Tue, 2018-06-12 at 09:00 -0700, Andy Lutomirski wrote:
> > On Tue, Jun 12, 2018 at 8:06 AM Yu-cheng Yu <yu-cheng.yu@intel.com> wrote:
> > >
> > > On Tue, 2018-06-12 at 20:56 +1000, Balbir Singh wrote:
> > > >
> > > > On 08/06/18 00:37, Yu-cheng Yu wrote:
> > > > > This series introduces CET - Shadow stack
> > > > >
> > > > > At the high level, shadow stack is:
> > > > >
> > > > >     Allocated from a task's address space with vm_flags VM_SHSTK;
> > > > >     Its PTEs must be read-only and dirty;
> > > > >     Fixed sized, but the default size can be changed by sys admin.
> > > > >
> > > > > For a forked child, the shadow stack is duplicated when the next
> > > > > shadow stack access takes place.
> > > > >
> > > > > For a pthread child, a new shadow stack is allocated.
> > > > >
> > > > > The signal handler uses the same shadow stack as the main program.
> > > > >
> > > >
> > > > Even with sigaltstack()?
> > > >
> > > >
> > > > Balbir Singh.
> > >
> > > Yes.
> > >
> >
> > I think we're going to need some provision to add an alternate signal
> > stack to handle the case where the shadow stack overflows.
>
> The shadow stack stores only return addresses; its consumption will not
> exceed a percentage of (program stack size + sigaltstack size) before
> those overflow.  When that happens, there is usually very little we can
> do.  So we set a default shadow stack size that supports certain nested
> calls and allow sys admin to adjust it.
>

Of course there's something you can do: add a sigaltstack-like stack
switching mechanism.  Have a reserve shadow stack and, when a signal
is delivered (possibly guarded by other conditions like "did the
shadow stack overflow"), switch to a new shadow stack and maybe write
a special token to the new shadow stack that says "signal delivery
jumped here and will restore to the previous shadow stack and
such-and-such address on return".

Also, I have a couple of other questions after reading the
documentation some more:

1. Why on Earth does INCSSP only take an 8-bit number of frames to
skip?  It seems to me that code that calls setjmp() and then calls
longjmp() while nested more than 256 function call levels will crash.

2. The mnemonic RSTORSSP makes no sense to me.  RSTORSSP is a stack
*switch* operation not a stack *restore* operation, unless I'm
seriously misunderstanding.

3. Is there anything resembling clear documentation of the format of
the shadow stack?  That is, what types of values might be found on the
shadow stack and what do they all mean?

4. Usually Intel doesn't submit upstream Linux patches for ISA
extensions until the ISA is documented for real.  CET does not appear
to be documented for real.  Could Intel kindly release something that
at least claims to be authoritative documentation?

--Andy

  reply	other threads:[~2018-06-12 16:31 UTC|newest]

Thread overview: 98+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-06-07 14:37 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
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 [this message]
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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