linux-kernel - Re: [PATCH v5 02/10] x86: Compile-time asm code validation

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20150610175320.GD29724@treble.redhat.com>
Date:	Wed, 10 Jun 2015 12:53:20 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Michal Marek <mmarek@...e.cz>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	live-patching@...r.kernel.org, X86 ML <x86@...nel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH v5 02/10] x86: Compile-time asm code validation

On Wed, Jun 10, 2015 at 10:21:36AM -0700, Andy Lutomirski wrote:
> On Jun 10, 2015 5:07 AM, "Josh Poimboeuf" <jpoimboe@...hat.com> wrote:
> >
> > Add a new CONFIG_ASM_VALIDATION option which adds an asmvalidate host
> > tool which runs on every compiled .S file.  Its goal is to enforce sane
> > rules on all asm code, so that stack debug metadata (frame/back chain
> > pointers and/or DWARF CFI metadata) can be made reliable.
> >
> > It enforces the following rules:
> >
> > 1. Each callable function must be annotated with the ELF STT_FUNC type.
> >    This is typically done using the ENTRY/ENDPROC macros.  If
> >    asmvalidate finds a return instruction outside of a function, it
> >    flags an error, since that usually indicates callable code which
> >    should be annotated accordingly.
> >
> > 2. Each callable function must never leave its own bounds (i.e. with a
> >    jump to outside the function) except when returning.
> 
> Won't that break with sibling/tail calls?

Yes, asmvalidate will flag a warning for tail calls.

> GCC can generate those, and the ia32_ptregs_common label is an example
> of such a thing.
> 
> I'd rather have the script understand tail calls and possibly require
> that ia32_ptregs_common have a dummy frame pointer save in front
> before the label if needed.

Why do you prefer tail calls there?  See patch 3 for how I handled that
for ia32_ptregs_common (I duplicated the code with macros).

I think adding support for tail calls in the tooling would be tricky.
So I'm just trying to figure out if there's a good reason to keep them.

-- 
Josh
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/