On Thu, May 31, 2018 at 10:07 PM, kbuild test robot <l...@intel.com> wrote:
> tree: https://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next.git
> master
> head: 4b8e6ac41a594ea67ded6af6af5935f03221ea4c
> commit: ccf8dbcd062a930e64741c939ca784d15316aa0c [375/376] rtnetlink: Remove
> VLA usage
> config: um-x86_64_defconfig (attached as .config)
> compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
> reproduce:
> git checkout ccf8dbcd062a930e64741c939ca784d15316aa0c
> # save the attached .config to linux build tree
> make ARCH=um SUBARCH=x86_64
>
> All warnings (new ones prefixed by >>):
>
> net/core/rtnetlink.c: In function 'rtnl_newlink':
>>> net/core/rtnetlink.c:3099:1: warning: the frame size of 1280 bytes is
>>> larger than 1024 bytes [-Wframe-larger-than=]
> }
> ^
The recent removal of the VLA has exposed how large it's possible for
this stack allocation to get (i.e. it was hidden from the checker
before because it was a VLA). This warning doesn't trip on regular
x86_64 because the -Wframe-larger-than is 2048. It seems like 64-bit
um should have the same 64-bit value (instead of using the 32-bit
value):
arch/um/configs/x86_64_defconfig:CONFIG_FRAME_WARN=1024
lib/Kconfig.debug:
config FRAME_WARN
int "Warn for stack frames larger than (needs gcc 4.4)"
range 0 8192
default 3072 if KASAN_EXTRA
default 2048 if GCC_PLUGIN_LATENT_ENTROPY
default 1280 if (!64BIT && PARISC)
default 1024 if (!64BIT && !PARISC)
default 2048 if 64BIT
Just dropping the defconfig there should fix it. (And I think it was
just a mistake to port that value when splitting the um defconfig in
commit e40f04d040c6 ("arch/um: make it work with defconfig and
x86_64").
-Kees
--
Kees Cook
Pixel Security
