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Message-ID: <CAGXu5jKfwBqEot+30z6Wh6Cow2gv25ojKxmoTS1Vb_LhwFiSnA@mail.gmail.com>
Date: Fri, 16 Dec 2016 14:19:10 -0800
From: Kees Cook <keescook@...omium.org>
To: "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>
Cc: Kees Cook <keescook@...omium.org>, LKML <linux-kernel@...r.kernel.org>,
Arnd Bergmann <arnd@...db.de>, Emese Revfy <re.emese@...il.com>,
Josh Triplett <josh@...htriplett.org>, PaX Team <pageexec@...email.hu>,
Brad Spengler <spender@...ecurity.net>, Michal Marek <mmarek@...e.com>,
Masahiro Yamada <yamada.masahiro@...ionext.com>, linux-kbuild <linux-kbuild@...r.kernel.org>,
minipli@...linux.so, Russell King <linux@...linux.org.uk>,
Catalin Marinas <catalin.marinas@....com>, Rasmus Villemoes <linux@...musvillemoes.dk>,
David Brown <david.brown@...aro.org>,
"benh@...nel.crashing.org" <benh@...nel.crashing.org>, Thomas Gleixner <tglx@...utronix.de>,
Andrew Morton <akpm@...ux-foundation.org>, Jeff Layton <jlayton@...chiereds.net>,
Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH v4 0/4] Introduce the initify gcc plugin
On Fri, Dec 16, 2016 at 2:06 PM, Kees Cook <keescook@...omium.org> wrote:
> Hi,
>
> This is a continuation of Emese Revfy's initify plugin upstreaming. This
> is based on her v3, but updated with various fixes from her github tree.
> Additionally, I split off the printf attribute fixes and sent those
> separately.
>
> This is the initify gcc plugin. The kernel already has a mechanism to
> free up code and data memory that is only used during kernel or module
> initialization. This plugin will teach the compiler to find more such
> code and data that can be freed after initialization. It reduces memory
> usage. The initify gcc plugin can be useful for embedded systems.
>
> Originally it was a CII project supported by the Linux Foundation.
>
> This plugin is the part of grsecurity/PaX.
>
> The plugin supports all gcc versions from 4.5 to 7.0.
>
> Changes on top of the PaX version (since March 6.). These are the important
> ones:
> * move all local strings to init.rodata.str and exit.rodata.str
> (not just __func__)
> * report all initified strings and functions
> (GCC_PLUGIN_INITIFY_VERBOSE config option)
> * automatically discover init/exit functions and apply the __init or
> __exit attributes on them
>
> You can find more about the changes here:
> https://github.com/ephox-gcc-plugins/initify
>
> This patch set is based on v4.9-rc2.
>
> Some build statistics about the plugin:
>
> On allyes config (amd64, gcc-6):
> * 8412 initified strings
> * 167 initified functions
>
> On allmod config (i386, gcc-6):
> * 8597 initified strings
> * 159 initified functions
>
> On allyes config (amd64, gcc-6):
>
> section vanilla vanilla + initify change
> -----------------------------------------------------------------------
> .rodata 21746728 (0x14bd428) 21488680 (0x147e428) -258048
> .init.data 1338376 (0x146c08) 1683016 (0x19ae48) +344640
> .text 78270904 (0x4aa51b8) 78228280 (0x4a9ab38) -42624
> .init.text 1184725 (0x1213d5) 1223257 (0x12aa59) +38532
> .exit.data 104 (0x000068) 17760 (0x004560) +17656
> .exit.text 174473 (0x02a989) 175763 (0x02ae93) +1290
>
> FileSiz (vanilla) FileSiz (vanilla + initify) change
> ------------------------------------------------------------------------
> 00 102936576 (0x622b000) 102678528 (0x61ec000) -258048
> 03 28680192 (0x1b5a000) 29081600 (0x1bbc000) +401408
>
> 00 .text .notes __ex_table .rodata __bug_table .pci_fixup .builtin_fw
> .tracedata __ksymtab __ksymtab_gpl __ksymtab_strings __init_rodata
> __param __modver
> 03 .init.text .altinstr_aux .init.data .x86_cpu_dev.init
> .parainstructions .altinstructions .altinstr_replacement
> .iommu_table .apicdrivers .exit.text .exit.data .smp_locks .bss .brk
>
>
> On defconfig (amd64, gcc-6):
> * 1957 initified strings
> * 29 initified functions
>
> On defconfig (amd64, gcc-6):
>
> section vanilla vanilla + initify change
> -----------------------------------------------------------------------
> .rodata 2524240 (0x268450) 2462800 (0x259450) -61440
> .init.data 560256 (0x088c80) 644000 (0x09d3a0) +83744
> .text 9377367 (0x8f1657) 9373079 (0x8f0597) -4288
> .init.text 438586 (0x06b13a) 441828 (0x06bde4) +3242
> .exit.data 0 832 (0x000340) +832
> .exit.text 8857 (0x002299) 8857 (0x002299) 0
>
> FileSiz (vanilla) FileSiz (vanilla + initify) change
> ------------------------------------------------------------------------
> 00 13398016 (0xcc7000) 13336576 (0xcb8000) -61440
> 03 2203648 (0x21a000) 2293760 (0x230000) +90112
>
> 00 .text .notes __ex_table .rodata __bug_table .pci_fixup .builtin_fw
> .tracedata __ksymtab __ksymtab_gpl __ksymtab_strings __init_rodata
> __param __modver
> 03 .init.text .altinstr_aux .init.data .x86_cpu_dev.init
> .parainstructions .altinstructions .altinstr_replacement
> .iommu_table .apicdrivers .exit.text .exit.data .smp_locks .bss .brk
>
> One thing of note is that this plugin triggers false positive warnings
> from the modpost section mismatch detector. Further work is needed to
> deal with this.
FWIW, it still seems to me that these aren't false positives:
WARNING: vmlinux.o(.text.unlikely+0x1b1): Section mismatch in
reference from the function uncore_pci_exit.part.22() to the function
.init.text:uncore_free_pcibus_map()
The function uncore_pci_exit.part.22() references
the function __init uncore_free_pcibus_map().
This is often because uncore_pci_exit.part.22 lacks a __init
annotation or the annotation of uncore_free_pcibus_map is wrong.
This is complaining about arch/x86/events/intel/uncore.c:
__init intel_uncore_init() calls uncore_pci_exit().
__exit intel_uncore_exit() calls uncore_pci_exit().
uncore_pci_exit() is marked as "both" (which will resolve to __exit).
__init intel_uncore_init() calls uncore_free_pcibus_map().
uncore_pci_exit() calls uncore_free_pcibus_map().
uncore_free_pcibus_map() should be marked as "both", but it seems like
it ends up marked only __init.
When I tried a build that looked only at -D MODULE being set, I got
fewer warnings, but the modpost on builtins would still have warnings,
but they complained about things in __exit calling __init, which for a
builtin is fine: the __exit section will never be called...
I think the modular-build checking is better than the Kconfig
approach. It just requires that the __exit sections for non-modules
get discarded before the modpost runs to complain about it...
-Kees
--
Kees Cook
Nexus Security
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