linux-kernel - Re: [RFC PATCH v6 22/26] x86/cet/shstk: ELF header parsing of Shadow Stack

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Date:   Thu, 25 Apr 2019 16:35:48 +0100
From:   Dave Martin <Dave.Martin@....com>
To:     Yu-cheng Yu <yu-cheng.yu@...el.com>
Cc:     x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-mm@...ck.org,
        linux-arch@...r.kernel.org, linux-api@...r.kernel.org,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Eugene Syromiatnikov <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v6 22/26] x86/cet/shstk: ELF header parsing of Shadow
 Stack

On Thu, Apr 25, 2019 at 08:14:52AM -0700, Yu-cheng Yu wrote:
> On Thu, 2019-04-25 at 12:02 +0100, Dave Martin wrote:
> > On Mon, Nov 19, 2018 at 01:48:05PM -0800, Yu-cheng Yu wrote:
> > > Look in .note.gnu.property of an ELF file and check if Shadow Stack needs
> > > to be enabled for the task.
> > 
> > What's the status of this series?  I don't see anything in linux-next
> > yet.
> > 
> > For describing ELF features, Arm has recently adopted
> > NT_GNU_PROPERTY_TYPE_0, with properties closely modelled on
> > GNU_PROPERTY_X86_FEATURE_1_AND etc. [1]
> > 
> > So, arm64 will be need something like this patch for supporting new
> > features (such as the Branch Target Identification feature of ARMv8.5-A
> > [2]).
> > 
> > If this series isn't likely to merge soon, can we split this patch into
> > generic and x86-specific parts and handle them separately?
> > 
> > It would be good to see the generic ELF note parsing move to common
> > code -- I'll take a look and comment in more detail.
> 
> Yes, I will work on that.

Thanks.  I may try to hack something in the meantime based on your
patch.

One other question: according to the draft spec at
https://github.com/hjl-tools/linux-abi/wiki/Linux-Extensions-to-gABI, it
looks like the .note.gnu.property section is supposed to be marked with
SHF_ALLOC in object files.

I think that means that the linker will map it with a PT_LOAD entry in
the program header table in addition to the PT_NOTE that describes the
location of the note.  I need to check what the toolchain actually
does.

If so, can we simply rely on the notes being already mapped, rather than
needing to do additional I/O on the ELF file to fetch the notes?

[...]

Cheers
---Dave