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From: Peter Zijlstra <peterz@infradead.org>
To: Kristen Carlson Accardi <kristen@linux.intel.com>
Cc: tglx@linutronix.de, mingo@redhat.com, bp@alien8.de,
	hpa@zytor.com, arjan@linux.intel.com, keescook@chromium.org,
	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: Thu, 6 Feb 2020 11:30:55 +0100
Message-ID: <20200206103055.GV14879@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200205223950.1212394-6-kristen@linux.intel.com>

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

The GCC manual has:

  -ffunction-sections
  -fdata-sections

      Place each function or data item into its own section in the output
      file if the target supports arbitrary sections. The name of the
      function or the name of the data item determines the section’s name
      in the output file.

      Use these options on systems where the linker can perform
      optimizations to improve locality of reference in the instruction
      space. Most systems using the ELF object format have linkers with
      such optimizations. On AIX, the linker rearranges sections (CSECTs)
      based on the call graph. The performance impact varies.

      Together with a linker garbage collection (linker --gc-sections
      option) these options may lead to smaller statically-linked
      executables (after stripping).

      On ELF/DWARF systems these options do not degenerate the quality of
      the debug information. There could be issues with other object
      files/debug info formats.

      Only use these options when there are significant benefits from
      doing so. When you specify these options, the assembler and linker
      create larger object and executable files and are also slower. These
      options affect code generation. They prevent optimizations by the
      compiler and assembler using relative locations inside a translation
      unit since the locations are unknown until link time. An example of
      such an optimization is relaxing calls to short call instructions.

In particular:

  "They prevent optimizations by the compiler and assembler using
  relative locations inside a translation unit since the locations are
  unknown until link time."

I suppose in practise this only means tail-calls are affected and will
no longer use JMP.d8. Or are more things affected?

(Also, should not the next patch come before this one?)

  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 [this message]
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
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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