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From: Kees Cook <keescook@chromium.org>
To: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: Arvind Sankar <nivedita@alum.mit.edu>,
	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 05/11] x86: Makefile: Add build and config option for CONFIG_FG_KASLR
Date: Wed, 25 Mar 2020 08:34:23 -0700
Message-ID: <202003250832.058B12D3@keescook> (raw)
In-Reply-To: <a01e6b2f0a19f0ace0b5f2c8a50cafccc9b4ef60.camel@linux.intel.com>

On Tue, Mar 24, 2020 at 02:24:51PM -0700, Kristen Carlson Accardi wrote:
> On Tue, 2020-02-25 at 12:55 -0500, Arvind Sankar wrote:
> > On Wed, Feb 05, 2020 at 02:39:44PM -0800, Kristen Carlson Accardi
> > wrote:
> > > Allow user to select CONFIG_FG_KASLR if dependencies are met.
> > > Change
> > > the make file to build with -ffunction-sections if CONFIG_FG_KASLR
> > > 
> > > Signed-off-by: Kristen Carlson Accardi <kristen@linux.intel.com>
> > > ---
> > >  Makefile         |  4 ++++
> > >  arch/x86/Kconfig | 13 +++++++++++++
> > >  2 files changed, 17 insertions(+)
> > > 
> > > diff --git a/Makefile b/Makefile
> > > index c50ef91f6136..41438a921666 100644
> > > --- a/Makefile
> > > +++ b/Makefile
> > > @@ -846,6 +846,10 @@ ifdef CONFIG_LIVEPATCH
> > >  KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone)
> > >  endif
> > >  
> > > +ifdef CONFIG_FG_KASLR
> > > +KBUILD_CFLAGS += -ffunction-sections
> > > +endif
> > > +
> > 
> > With -ffunction-sections I get a few unreachable code warnings from
> > objtool.
> > 
> > [...]
> > net/mac80211/ibss.o: warning: objtool:
> > ieee80211_ibss_work.cold()+0x157: unreachable instruction
> > drivers/net/ethernet/intel/e1000/e1000_main.o: warning: objtool:
> > e1000_clean.cold()+0x0: unreachable instruction
> > net/core/skbuff.o: warning: objtool: skb_dump.cold()+0x3fd:
> > unreachable instruction
> 
> I'm still working on a solution, but the issue here is that any .cold
> function is going to be in a different section than the related
> function, and when objtool is searching for instructions in
> find_insn(), it assumes that it must be in the same section as the
> caller.

Can we teach objtool about this? It doesn't seem too unreasonable.

-- 
Kees Cook

  reply index

Thread overview: 73+ 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
2020-02-07  7:23     ` Jean-Philippe Aumasson
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 [this message]
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
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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