From: Arvind Sankar <nivedita@alum.mit.edu>
To: Arvind Sankar <nivedita@alum.mit.edu>
Cc: Kees Cook <keescook@chromium.org>,
Kristen Carlson Accardi <kristen@linux.intel.com>,
tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
hpa@zytor.com, arjan@linux.intel.com, rick.p.edgecombe@intel.com,
x86@kernel.org, linux-kernel@vger.kernel.org,
kernel-hardening@lists.openwall.com
Subject: Re: [RFC PATCH 06/11] x86: make sure _etext includes function sections
Date: Thu, 6 Feb 2020 10:45:47 -0500 [thread overview]
Message-ID: <20200206154547.GA3064177@rani.riverdale.lan> (raw)
In-Reply-To: <20200206145738.GA3049612@rani.riverdale.lan>
On Thu, Feb 06, 2020 at 09:57:40AM -0500, Arvind Sankar wrote:
> On Thu, Feb 06, 2020 at 04:26:23AM -0800, Kees Cook wrote:
> > On Wed, Feb 05, 2020 at 02:39:45PM -0800, Kristen Carlson Accardi wrote:
> > > We will be using -ffunction-sections to place each function in
> > > it's own text section so it can be randomized at load time. The
> > > linker considers these .text.* sections "orphaned sections", and
> > > will place them after the first similar section (.text). However,
> > > we need to move _etext so that it is after both .text and .text.*
> > > We also need to calculate text size to include .text AND .text.*
> >
> > The dependency on the linker's orphan section handling is, I feel,
> > rather fragile (during work on CFI and generally building kernels with
> > Clang's LLD linker, we keep tripping over difference between how BFD and
> > LLD handle orphans). However, this is currently no way to perform a
> > section "pass through" where input sections retain their name as an
> > output section. (If anyone knows a way to do this, I'm all ears).
> >
> > Right now, you can only collect sections like this:
> >
> > .text : AT(ADDR(.text) - LOAD_OFFSET) {
> > *(.text.*)
> > }
> >
> > or let them be orphans, which then the linker attempts to find a
> > "similar" (code, data, etc) section to put them near:
> > https://sourceware.org/binutils/docs-2.33.1/ld/Orphan-Sections.html
> >
> > So, basically, yes, this works, but I'd like to see BFD and LLD grow
> > some kind of /PASSTHRU/ special section (like /DISCARD/), that would let
> > a linker script specify _where_ these sections should roughly live.
> >
>
> You could go through the objects that are being linked and find the
> individual text sections, and generate the linker script using that?
Also, one thing to note about the orphan section handling -- by default
ld will combine multiple orphan sections with the same name into a
single output section. So if you have sections corresponding to static
functions with the same name but from different files, they will get
unnecessarily combined. You may want to add --unique to the ld options
to keep them separate. That will create multiple sections with the same
name instead of merging them.
next prev parent reply other threads:[~2020-02-06 15:45 UTC|newest]
Thread overview: 72+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-05 22:39 [RFC PATCH 00/11] Finer grained kernel address space randomization Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 01/11] modpost: Support >64K sections Kristen Carlson Accardi
2020-02-06 12:38 ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 02/11] x86: tools/relocs: Support >64K section headers Kristen Carlson Accardi
2020-02-06 12:39 ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 03/11] x86/boot: Allow a "silent" kaslr random byte fetch Kristen Carlson Accardi
2020-02-06 1:08 ` Andy Lutomirski
2020-02-06 11:48 ` Kees Cook
2020-02-06 16:58 ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 04/11] x86/boot/KASLR: Introduce PRNG for faster shuffling Kristen Carlson Accardi
2020-02-06 1:11 ` Andy Lutomirski
2020-02-06 15:10 ` Jason A. Donenfeld
[not found] ` <CAGiyFdes26XnNeDfaz-vkm+bU7MBYQiK3xty2EigGjOXBGui2w@mail.gmail.com>
2020-02-07 9:05 ` Kees Cook
2020-02-07 16:52 ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR Kristen Carlson Accardi
2020-02-06 10:30 ` Peter Zijlstra
2020-02-06 11:52 ` Kees Cook
2020-02-25 17:55 ` Arvind Sankar
2020-02-26 19:13 ` Kristen Carlson Accardi
2020-03-24 21:24 ` Kristen Carlson Accardi
2020-03-25 15:34 ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 06/11] x86: make sure _etext includes function sections Kristen Carlson Accardi
2020-02-06 12:26 ` Kees Cook
2020-02-06 13:15 ` Jann Horn
2020-02-06 16:27 ` David Laight
2020-02-06 14:39 ` Arvind Sankar
2020-02-06 15:29 ` Arvind Sankar
2020-02-06 16:11 ` Andy Lutomirski
2020-02-06 14:57 ` Arvind Sankar
2020-02-06 15:45 ` Arvind Sankar [this message]
2020-02-06 19:41 ` Kristen Carlson Accardi
2020-02-06 20:02 ` Andy Lutomirski
2020-02-07 9:24 ` Peter Zijlstra
2020-02-10 1:43 ` Kees Cook
2020-02-10 10:51 ` Peter Zijlstra
2020-02-10 15:54 ` Arjan van de Ven
2020-02-10 16:36 ` Arvind Sankar
2020-02-21 19:50 ` Josh Poimboeuf
2020-02-21 23:05 ` Arvind Sankar
2020-02-05 22:39 ` [RFC PATCH 07/11] x86/tools: Adding relative relocs for randomized functions Kristen Carlson Accardi
2020-02-06 12:37 ` Kees Cook
2020-02-05 22:39 ` [RFC PATCH 08/11] x86: Add support for finer grained KASLR Kristen Carlson Accardi
2020-02-06 1:17 ` Andy Lutomirski
2020-02-06 11:56 ` Kees Cook
2020-02-06 17:36 ` Kristen Carlson Accardi
2020-02-06 10:38 ` Peter Zijlstra
2020-02-06 12:06 ` Kees Cook
2020-02-06 14:52 ` Peter Zijlstra
2020-02-06 17:25 ` Kristen Carlson Accardi
2020-02-06 17:35 ` Peter Zijlstra
2020-02-06 17:43 ` Kristen Carlson Accardi
2020-02-25 17:49 ` Arvind Sankar
2020-02-26 19:26 ` Kristen Carlson Accardi
2020-02-05 22:39 ` [RFC PATCH 09/11] kallsyms: hide layout and expose seed Kristen Carlson Accardi
2020-02-06 12:32 ` Kees Cook
2020-02-06 17:51 ` Kristen Carlson Accardi
2020-02-06 19:27 ` Jann Horn
2020-03-02 19:01 ` Kristen Carlson Accardi
2020-03-02 19:08 ` Kees Cook
2020-03-02 19:19 ` Kristen Carlson Accardi
2020-02-27 2:42 ` Baoquan He
2020-02-27 16:02 ` Kees Cook
2020-02-28 3:36 ` Baoquan He
2020-02-05 22:39 ` [RFC PATCH 10/11] module: Reorder functions Kristen Carlson Accardi
2020-02-06 12:41 ` Kees Cook
2020-02-11 12:39 ` Jessica Yu
2020-02-05 22:39 ` [RFC PATCH 11/11] x86/boot: Move "boot heap" out of .bss Kristen Carlson Accardi
2020-02-06 0:11 ` Arvind Sankar
2020-02-06 0:33 ` Kristen Carlson Accardi
2020-02-06 11:13 ` Kees Cook
2020-02-06 14:25 ` Arvind Sankar
2020-02-06 21:32 ` Kees Cook
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