Re: [RFC PATCH v6 01/26] Documentation/x86: Add CET description

[Ingo Molnar]

* Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx> wrote:

> +X86 Documentation
> +=======================
> +
> +Control-flow Enforcement
> +========================
> +
> +.. toctree::
> +   :maxdepth: 1
> +
> +   intel_cet
> diff --git a/Documentation/x86/intel_cet.rst b/Documentation/x86/intel_cet.rst
> new file mode 100644
> index 000000000000..dac83bbf8a24
> --- /dev/null
> +++ b/Documentation/x86/intel_cet.rst
> @@ -0,0 +1,268 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========================================
> +Control-flow Enforcement Technology (CET)
> +=========================================
> +
> +[1] Overview
> +============
> +
> +Control-flow Enforcement Technology (CET) provides protection against
> +return/jump-oriented programming (ROP) attacks.  It can be setup to
> +protect both the kernel and applications.  In the first phase,
> +only the user-mode protection is implemented in 64-bit mode; 32-bit
> +applications are supported in compatibility mode.
> +
> +CET introduces shadow stack (SHSTK) and indirect branch tracking
> +(IBT).  SHSTK is a secondary stack allocated from memory and cannot
> +be directly modified by applications.  When executing a CALL, the
> +processor pushes a copy of the return address to SHSTK.  Upon
> +function return, the processor pops the SHSTK copy and compares it
> +to the one from the program stack.  If the two copies differ, the
> +processor raises a control-protection exception.  IBT verifies all
> +indirect CALL/JMP targets are intended as marked by the compiler
> +with 'ENDBR' opcodes (see CET instructions below).
> +
> +There are two kernel configuration options:
> +
> +    INTEL_X86_SHADOW_STACK_USER, and
> +    INTEL_X86_BRANCH_TRACKING_USER.
> +
> +To build a CET-enabled kernel, Binutils v2.31 and GCC v8.1 or later
> +are required.  To build a CET-enabled application, GLIBC v2.28 or
> +later is also required.
> +
> +There are two command-line options for disabling CET features:
> +
> +    no_cet_shstk - disables SHSTK, and
> +    no_cet_ibt - disables IBT.
> +
> +At run time, /proc/cpuinfo shows the availability of SHSTK and IBT.

What is the rough expected performance impact of CET on average function 
call frequency user applications and the kernel itself?

Thanks,

	Ingo