From: Dave Hansen <dave.hansen@intel.com>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>,
linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org,
linux-mm@kvack.org, linux-arch@vger.kernel.org,
linux-api@vger.kernel.org, Arnd Bergmann <arnd@arndb.de>,
Andy Lutomirski <luto@kernel.org>,
Balbir Singh <bsingharora@gmail.com>,
Borislav Petkov <bp@alien8.de>,
Cyrill Gorcunov <gorcunov@gmail.com>,
Dave Hansen <dave.hansen@linux.intel.com>,
Eugene Syromiatnikov <esyr@redhat.com>,
Florian Weimer <fweimer@redhat.com>,
"H.J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.com>,
Jonathan Corbet <corbet@lwn.net>,
Kees Cook <keescook@chromium.org>,
Mike Kravetz <mike.kravetz@oracle.com>,
Nadav Amit <nadav.amit@gmail.com>,
Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
Peter Zijlstra <peterz@infradead.org>,
Randy Dunlap <rdunlap@infradead.org>,
"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
Vedvyas Shanbhogue <vedvyas.shanbhogue@intel.com>,
Dave Martin <Dave.Martin@arm.com>,
Weijiang Yang <weijiang.yang@intel.com>
Subject: Re: [PATCH v10 01/26] Documentation/x86: Add CET description
Date: Fri, 15 May 2020 15:43:56 -0700 [thread overview]
Message-ID: <32235ffc-6e6c-fb3d-80c4-a0478e2d0e0f@intel.com> (raw)
In-Reply-To: <44c055342bda4fb4730703f987ae35195d1d0c38.camel@intel.com>
On 5/15/20 2:33 PM, Yu-cheng Yu wrote:
> On Fri, 2020-05-15 at 11:39 -0700, Dave Hansen wrote:
>> On 5/12/20 4:20 PM, Yu-cheng Yu wrote:
>> Can a binary compiled with CET run without CET?
>
> Yes, but a few details:
>
> - The shadow stack is transparent to the application. A CET application does
> not have anything different from a non-CET application. However, if a CET
> application uses any CET instructions (e.g. INCSSP), it must first check if CET
> is turned on.
> - If an application is compiled for IBT, the compiler inserts ENDBRs at branch
> targets. These are nops if IBT is not on.
I appreciate the detailed response, but it wasn't quite what I was
asking. Let's ignore IBT for now and just talk about shadow stacks.
An app compiled with the new ELF flags and running on a CET-enabled
kernel and CPU will start off with shadow stacks allocated and enabled,
right? It can turn its shadow stack off per-thread with the new prctl.
But, otherwise, it's stuck, the only way to turn shadow stacks off at
startup would be editing the binary.
Basically, if there ends up being a bug in an app that violates the
shadow stack rules, the app is broken, period. The only recourse is to
have the kernel disable CET and reboot.
Is that right?
>> Can a binary compiled without CET run CET-enabled code?
>
> Partially yes, but in reality somewhat difficult.
...
> - If a not-CET application does fork(), and the child wants to turn on CET, it
> would be difficult to manage the stack frames, unless the child knows what is is
> doing.
It might be hard to do, but it is possible with the patches you posted?
I think you're saying that the CET-enabled binary would do
arch_setup_elf_property() when it was first exec()'d. Later, it could
use the new prctl(ARCH_X86_CET_DISABLE) to disable its shadow stack,
then fork() and the child would not be using CET. Right?
What is ARCH_X86_CET_DISABLE used for, anyway?
> The JIT examples I mentioned previously run with CET enabled from the
> beginning. Do you have a reason to do this? In other words, if the JIT code
> needs CET, the app could have started with CET in the first place.
Let's say I have a JIT'd sandbox. I want the sandbox to be
CET-protected, but the JIT engine itself not to be.
> - If you are asking about dlopen(), the library will have the same setting as
> the main application. Do you have any reason to have a library running with
> CET, but the application does not have CET?
Sure, using old binaries. That's why IBT has a legacy bitmap and things
like MPX had ways of jumping into old non-enabled binaries.
>> Can different threads in a process have different CET enabling state?
>
> Yes, if the parent starts with CET, children can turn it off.
How would that work, though? clone() by default will copy the parent
xsave state, which means it will be CET-enabled, which means it needs a
shadow stack. So, if I want a CET-free child thread, I need to clone(),
then turn CET off, then free the shadow stack?
>> Does this *code* work? Could you please indicate which JITs have been
>> enabled to use the code in this series? How much of the new ABI is in use?
>
> JIT does not necessarily use all of the ABI. The JIT changes mainly fix stack
> frames and insert ENDBRs. I do not work on JIT. What I found is LLVM JIT fixes
> are tested and in the master branch. Sljit fixes are in the release.
Huh, so who is using the new prctl() ABIs?
>> Where are the selftests/ for this new ABI? Were you planning on
>> submitting any with this series?
>
> The ABI is more related to the application side, and therefore most suitable for
> GLIBC unit tests.
I was mostly concerned with the kernel selftests. The things in
tools/testing/selftests/x86 in the kernel tree.
> The more complicated areas such as pthreads, signals, ucontext,
> fork() are all included there. I have been constantly running these
> tests without any problems. I can provide more details if testing is
> the concern.
For something this complicated, with new kernel ABIs, we need an
in-kernel sefltest.
MPX was not that much different from this feature. It required a
boatload of compiler and linker changes to function. Yet, there was a
simple in-kernel test for it that didn't require *any* of that big pile
of toolchain bits.
Is there a reason we don't have one of those for CET?
next prev parent reply other threads:[~2020-05-15 22:44 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-29 22:07 [PATCH v10 00/26] Control-flow Enforcement: Shadow Stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 01/26] Documentation/x86: Add CET description Yu-cheng Yu
2020-04-29 22:53 ` Dave Hansen
2020-04-29 23:02 ` Yu-cheng Yu
2020-05-12 23:20 ` Yu-cheng Yu
2020-05-15 18:39 ` Dave Hansen
2020-05-15 21:33 ` Yu-cheng Yu
2020-05-15 22:43 ` Dave Hansen [this message]
2020-05-15 23:29 ` Yu-cheng Yu
2020-05-15 23:56 ` Dave Hansen
2020-05-16 2:51 ` H.J. Lu
2020-05-17 23:09 ` Dave Hansen
2020-05-16 2:53 ` Yu-cheng Yu
2020-05-18 13:41 ` Dave Hansen
2020-05-18 14:01 ` H.J. Lu
2020-05-18 14:26 ` Dave Hansen
2020-05-18 14:21 ` Yu-cheng Yu
2020-05-18 23:47 ` Yu-cheng Yu
2020-05-19 0:38 ` Dave Hansen
2020-05-19 1:35 ` Andy Lutomirski
2020-05-20 1:04 ` Andy Lutomirski
2020-05-29 2:08 ` Yu-cheng Yu
2020-05-16 0:13 ` Andrew Cooper
2020-05-16 2:37 ` H.J. Lu
2020-05-16 14:09 ` Andrew Cooper
2020-05-22 16:49 ` Peter Zijlstra
2020-05-22 17:48 ` Andrew Cooper
2020-04-29 22:07 ` [PATCH v10 02/26] x86/cpufeatures: Add CET CPU feature flags for Control-flow Enforcement Technology (CET) Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 03/26] x86/fpu/xstate: Introduce CET MSR XSAVES supervisor states Yu-cheng Yu
2020-07-23 16:10 ` Sean Christopherson
2020-07-23 16:21 ` Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 04/26] x86/cet: Add control-protection fault handler Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 05/26] x86/cet/shstk: Add Kconfig option for user-mode Shadow Stack Yu-cheng Yu
2020-05-07 15:55 ` Dave Hansen
2020-05-07 16:59 ` Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 06/26] x86/mm: Change _PAGE_DIRTY to _PAGE_DIRTY_HW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 07/26] x86/mm: Remove _PAGE_DIRTY_HW from kernel RO pages Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 08/26] x86/mm: Introduce _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 09/26] drm/i915/gvt: Change _PAGE_DIRTY to _PAGE_DIRTY_BITS Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 10/26] x86/mm: Update pte_modify for _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 11/26] x86/mm: Update ptep_set_wrprotect() and pmdp_set_wrprotect() for transition from _PAGE_DIRTY_HW to _PAGE_COW Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 12/26] mm: Introduce VM_SHSTK for shadow stack memory Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 13/26] x86/mm: Shadow Stack page fault error checking Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 14/26] x86/mm: Update maybe_mkwrite() for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 15/26] mm: Fixup places that call pte_mkwrite() directly Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 16/26] mm: Add guard pages around a shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 17/26] mm/mmap: Add shadow stack pages to memory accounting Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 18/26] mm: Update can_follow_write_pte() for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 19/26] x86/cet/shstk: User-mode shadow stack support Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 20/26] x86/cet/shstk: Handle signals for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 21/26] ELF: UAPI and Kconfig additions for ELF program properties Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 22/26] ELF: Add ELF program property parsing support Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 23/26] ELF: Introduce arch_setup_elf_property() Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 24/26] x86/cet/shstk: ELF header parsing for shadow stack Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 25/26] x86/cet/shstk: Handle thread " Yu-cheng Yu
2020-04-29 22:07 ` [PATCH v10 26/26] x86/cet/shstk: Add arch_prctl functions for " Yu-cheng Yu
2020-05-21 22:42 ` Kees Cook
2020-05-22 17:17 ` Yu-cheng Yu
2020-05-22 17:29 ` Eugene Syromiatnikov
2020-05-22 18:13 ` Yu-cheng Yu
2020-05-21 15:15 ` [PATCH v10 00/26] Control-flow Enforcement: Shadow Stack Josh Poimboeuf
2020-05-21 15:57 ` Yu-cheng Yu
2020-05-21 18:50 ` Josh Poimboeuf
2020-05-21 19:08 ` Yu-cheng Yu
2020-07-23 16:25 ` Sean Christopherson
2020-07-23 16:41 ` Dave Hansen
2020-07-23 16:56 ` Sean Christopherson
2020-07-23 18:41 ` Dave Hansen
2020-07-24 3:40 ` Yu-cheng Yu
2020-07-24 4:50 ` Sean Christopherson
2020-07-24 4:59 ` Sean Christopherson
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