Linux-api Archive on lore.kernel.org
 help / color / Atom feed
From: "H.J. Lu" <hjl.tools@gmail.com>
To: Dave Hansen <dave.hansen@intel.com>
Cc: Yu-cheng Yu <yu-cheng.yu@intel.com>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	linux-arch <linux-arch@vger.kernel.org>,
	Linux API <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>, 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: Mon, 18 May 2020 07:01:26 -0700
Message-ID: <CAMe9rOpX_6Zn69ZzwVt5Rdh5B9HwU7ccyoQLfyM067G8A=Eg-Q@mail.gmail.com> (raw)
In-Reply-To: <6f2ef0e5-d3bb-2b52-dc81-8228fec4a3f5@intel.com>

On Mon, May 18, 2020 at 6:41 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> On 5/15/20 7:53 PM, Yu-cheng Yu wrote:
> > On Fri, 2020-05-15 at 16:56 -0700, Dave Hansen wrote:
> >> What's my recourse as an end user?  I want to run my app and turn off
> >> CET for that app.  How can I do that?
> >
> > GLIBC_TUNABLES=glibc.tune.hwcaps=-SHSTK,-IBT
>
> Like I mentioned to H.J., this is something that we need to at least
> acknowledge the existence of in the changelog and probably even the
> Documentation/.
>
> >>>>  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?
> >>>
> >>> Both the parent and the child can do ARCH_X86_CET_DISABLE, if CET is
> >>> not locked.
> >>
> >> Could you please describe a real-world example of why
> >> ARCH_X86_CET_DISABLE exists?  What kinds of apps will use it, or *are*
> >> using it?  Why was it created in the first place?
> >
> > Currently, ld-linux turns off CET if the binary being loaded does not support
> > CET.
>
> Great!  Could this please be immortalized in the documentation for the
> prctl()?
>
> >>>>>> 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?
> >>>
> >>> Any code can use the ABI, but JIT code CET-enabling part mostly do not use these
> >>> new prctl()'s, except, probably to get CET status.
> >>
> >> Which applications specifically are going to use the new prctl()s which
> >> this series adds?  How are they going to use them?
> >>
> >> "Any code can use them" is not a specific enough answer.
> >
> > We have four arch_ptctl() calls.  ARCH_X86_CET_DISABLE and ARCH_X86_CET_LOCK are
> > used by ld-linux.  ARCH_X86_CET_STATUS are used in many places to determine if
> > CET is on.  ARCH_X86_CET_ALLOC_SHSTK is used in ucontext related handling, but
> > it can be use by any application to switch shadow stacks.
>
> Could some of this information be added to the documentation, please?
> It would also be nice to have some more details about how apps end up
> using ARCH_X86_CET_STATUS.  Why would they care that CET is on?

CET software spec is at

https://gitlab.com/x86-psABIs/x86-64-ABI/-/wikis/Intel-CET-extension

My CET presentation at 2018 LPC is at

https://www.linuxplumbersconf.org/event/2/contributions/147/attachments/72/83/CET-LPC-2018.pdf

I am working on an updated CET presentation for 2020 LPC.  Let me know
if you want to see the early draft.

-- 
H.J.

  reply index

Thread overview: 62+ 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
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 [this message]
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
2020-04-29 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

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='CAMe9rOpX_6Zn69ZzwVt5Rdh5B9HwU7ccyoQLfyM067G8A=Eg-Q@mail.gmail.com' \
    --to=hjl.tools@gmail.com \
    --cc=Dave.Martin@arm.com \
    --cc=arnd@arndb.de \
    --cc=bp@alien8.de \
    --cc=bsingharora@gmail.com \
    --cc=corbet@lwn.net \
    --cc=dave.hansen@intel.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=esyr@redhat.com \
    --cc=fweimer@redhat.com \
    --cc=gorcunov@gmail.com \
    --cc=hpa@zytor.com \
    --cc=jannh@google.com \
    --cc=keescook@chromium.org \
    --cc=linux-api@vger.kernel.org \
    --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=nadav.amit@gmail.com \
    --cc=oleg@redhat.com \
    --cc=pavel@ucw.cz \
    --cc=peterz@infradead.org \
    --cc=ravi.v.shankar@intel.com \
    --cc=rdunlap@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=vedvyas.shanbhogue@intel.com \
    --cc=weijiang.yang@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

Linux-api Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-api/0 linux-api/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-api linux-api/ https://lore.kernel.org/linux-api \
		linux-api@vger.kernel.org
	public-inbox-index linux-api

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-api


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git