Re: [RFC PATCH v3 05/24] Documentation/x86: Add CET description
From: Pavel Machek
Date: Thu Aug 30 2018 - 16:39:55 EST
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 9871e649ffef..b090787188b4 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2764,6 +2764,12 @@
> noexec=on: enable non-executable mappings (default)
> noexec=off: disable non-executable mappings
> + no_cet_ibt [X86-64] Disable indirect branch tracking for user-mode
> + applications
> + no_cet_shstk [X86-64] Disable shadow stack support for user-mode
> + applications
Hmm, not too consistent with "nosmap" below. Would it make sense to
have cet=on/off/ibt/shstk instead?
> +++ b/Documentation/x86/intel_cet.rst
> @@ -0,0 +1,252 @@
> +Control Flow Enforcement Technology (CET)
> + Overview
> +Control Flow Enforcement Technology (CET) provides protection against
> +return/jump-oriented programing (ROP) attacks.
Can you add something like "It attempts to protect process from
running arbitrary code even after attacker has control of its stack"
-- for people that don't know what ROP is, and perhaps link to
wikipedia explaining ROP or something...
> It can be implemented
> +to protect both the kernel and applications. In the first phase,
> +only the user-mode protection is implemented for the 64-bit kernel.
> +Thirty-two bit applications are supported under the compatibility
32-bit (for consistency).
Ok, so CET stops execution of malicious code before architectural
effects are visible, correct? Does it prevent micro-architectural
effects of the malicious code? (cache content would be one example;
> + Application Enabling
"Enabling CET in applications" ?
> +The main program and its signal handlers use the same SHSTK. Because
> +the SHSTK stores only return addresses, we can estimate a large
> +enough SHSTK to cover the condition that both the program stack and
> +the sigaltstack run out.
English? Is it estimate or is it large enough? "a large" -- "a" should
be deleted AFAICT.
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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