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Message-ID: <2b452e83-d74a-8d41-1f00-1764b2c767f1@redhat.com>
Date: Mon, 19 Dec 2016 10:24:05 -0800
From: Laura Abbott <labbott@...hat.com>
To: Kees Cook <keescook@...omium.org>, kernel-hardening@...ts.openwall.com
Cc: linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
Emese Revfy <re.emese@...il.com>, Josh Triplett <josh@...htriplett.org>,
pageexec@...email.hu, spender@...ecurity.net, mmarek@...e.com,
yamada.masahiro@...ionext.com, linux-kbuild@...r.kernel.org,
minipli@...linux.so, linux@...linux.org.uk, catalin.marinas@....com,
linux@...musvillemoes.dk, david.brown@...aro.org, benh@...nel.crashing.org,
tglx@...utronix.de, akpm@...ux-foundation.org, jlayton@...chiereds.net,
sam@...nborg.org
Subject: Re: [PATCH v4 0/4] Introduce the initify gcc plugin
On 12/16/2016 02:06 PM, Kees Cook 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.
>
>
> Changed from v3:
> * Refresh from Emese's latest version.
>
> Changed from v2:
> * Check all uses when walking a use-def chain.
> * Check all uses of initialized local variables and initify them if they
> have only nocapture uses. Previously only uses in call arguments
> determined whether the initializer value could be initified.
> * Handle the format gcc attribute from the plugin too.
> * Verify nocapture parameters of calls. Track uses of these parameters
> and verify that all uses are not captured. Verify only the nocapture
> attribute (The format attribute should be verified too.).
> * Fixed wrong indexing of function arguments.
> * Fixed decl comparison. When comparing two decls the tree codes must be
> the same.
> * Search capture uses of the return value. Use negative nocapture
> attribute parameter on a function argument to verify that the return
> value is not captured.
> * Stop the search for capture uses if there is a cast to integer type.
> * Removed unnecessary duplication hook.
> * Handle cloned functions with a changed argument list.
> * Check visited tree nodes to avoid an infinite loop.
> * Add a new initify plugin option: enable_init_to_exit_moves. Move a
> function to the exit section if it is called by __init and __exit
> functions too.
> * Added plugin option to disable the search of capture uses in nocapture
> functions. We must be able to disable verification of nocapture
> functions because there is a lot of asm code in the str* and mem*
> functions on i386.
> * Added some more nocapture attributes.
> * Added some more printf attributes.
> * Added some unverified_nocapture attributes.
> * Make is_kernel_rodata() nocapture.
> * Added comment for the nocapture attribute from Kees.
>
> Changes from v1:
> * Removed unnecessary nocapture attributes from boot code
> (Reported-by: PaX Team <pageexec@...email.hu>)
> * Removed nocapture attributes from functions that return
> the marked parameter
> (Reported-by: Rasmus Villemoes <linux@...musvillemoes.dk>)
> * Added nocapture attribute to strlen()
> * Updated gcc-common.h from PaX
> * Don't forcibly constify initified string types
> this caused the size reduction of the .data section
> (initify_plugin.c)
> * Added the section mismatch problem in the commit message
>
I gave this a spin on arm64 and it seems to boot up and run okay
with just the "select HAVE_GCC_PLUGIN_INITIFY_INIT_EXIT if GCC_PLUGINS"
added for arm64. The patches could probably use more review but
I think it would be good to just fold this in for arm64 for ease of
testing.
Thanks,
Laura
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