linux-hardening - Re: [RFC 0/3] kunit vs structleak

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Date:   Wed, 27 Jan 2021 12:15:15 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Arnd Bergmann <arnd@...nel.org>
Cc:     linux-kernel@...r.kernel.org, Arnd Bergmann <arnd@...db.de>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        Shuah Khan <skhan@...uxfoundation.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Alan Maguire <alan.maguire@...cle.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Vitor Massaru Iha <vitor@...saru.org>,
        linux-hardening@...r.kernel.org, linux-kselftest@...r.kernel.org,
        kunit-dev@...glegroups.com
Subject: Re: [RFC 0/3] kunit vs structleak

On Mon, Jan 25, 2021 at 01:45:25PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@...db.de>
> 
> I ran into a couple of problems with kunit tests taking too much stack
> space, sometimes dangerously so. These the the three instances that
> cause an increase over the warning limit of some architectures:
> 
> lib/bitfield_kunit.c:93:1: error: the frame size of 7440 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> drivers/base/test/property-entry-test.c:481:1: error: the frame size of 2640 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> drivers/thunderbolt/test.c:1529:1: error: the frame size of 1176 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> 
> Ideally there should be a way to rewrite the kunit infrastructure
> that avoids the explosion of stack data when the structleak plugin
> is used.
> 
> A rather drastic measure would be to use Kconfig logic to make
> the two options mutually exclusive. This would clearly work, but
> is probably not needed.
> 
> As a simpler workaround, this disables the plugin for the three
> files in which the excessive stack usage was observed.
> 
>       Arnd
> 
> Arnd Bergmann (3):
>   bitfield: build kunit tests without structleak plugin
>   drivers/base: build kunit tests without structleak plugin
>   thunderbolt: build kunit tests without structleak plugin
> 
>  drivers/base/test/Makefile   | 1 +
>  drivers/thunderbolt/Makefile | 1 +
>  lib/Makefile                 | 1 +
>  3 files changed, 3 insertions(+)

I think I'd prefer centralizing the disabling, as done with the other
plugins, instead of sprinkling "open coded" command-line options around
the kernel's Makefiles. :)

For example:


diff --git a/scripts/Makefile.gcc-plugins b/scripts/Makefile.gcc-plugins
index 952e46876329..2d5009e3b593 100644
--- a/scripts/Makefile.gcc-plugins
+++ b/scripts/Makefile.gcc-plugins
@@ -21,6 +21,10 @@ gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK_BYREF_ALL)	\
 		+= -fplugin-arg-structleak_plugin-byref-all
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_STRUCTLEAK)		\
 		+= -DSTRUCTLEAK_PLUGIN
+ifdef CONFIG_GCC_PLUGIN_STRUCTLEAK
+    DISABLE_STRUCTLEAK_PLUGIN += -fplugin-arg-structleak_plugin-disable
+endif
+export DISABLE_STRUCTLEAK_PLUGIN
 
 gcc-plugin-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)	+= randomize_layout_plugin.so
 gcc-plugin-cflags-$(CONFIG_GCC_PLUGIN_RANDSTRUCT)		\


And then use DISABLE_STRUCTLEAK_PLUGIN.

-- 
Kees Cook