From: Kees Cook <keescook@chromium.org>
To: Arnd Bergmann <arnd@arndb.de>
Cc: James Morris <jmorris@namei.org>,
"Serge E. Hallyn" <serge@hallyn.com>,
James Smart <james.smart@broadcom.com>,
Dick Kennedy <dick.kennedy@broadcom.com>,
"James E . J . Bottomley" <jejb@linux.ibm.com>,
"Martin K . Petersen" <martin.petersen@oracle.com>,
Larry Finger <Larry.Finger@lwfinger.net>,
Florian Schilhabel <florian.c.schilhabel@googlemail.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
"David S . Miller" <davem@davemloft.net>,
Wensong Zhang <wensong@linux-vs.org>,
Simon Horman <horms@verge.net.au>, Julian Anastasov <ja@ssi.bg>,
Pablo Neira Ayuso <pablo@netfilter.org>,
linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
devel@driverdev.osuosl.org, netdev@vger.kernel.org,
lvs-devel@vger.kernel.org, netfilter-devel@vger.kernel.org,
coreteam@netfilter.org,
Ard Biesheuvel <ard.biesheuvel@linaro.org>,
Masahiro Yamada <yamada.masahiro@socionext.com>,
Alexander Potapenko <glider@google.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
Thomas Gleixner <tglx@linutronix.de>,
linux-security-module@vger.kernel.org
Subject: Re: [PATCH 1/4] [v2] structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK
Date: Fri, 28 Jun 2019 07:48:33 -0700 [thread overview]
Message-ID: <201906280748.910641F1DD@keescook> (raw)
In-Reply-To: <20190628123819.2785504-1-arnd@arndb.de>
On Fri, Jun 28, 2019 at 02:37:46PM +0200, Arnd Bergmann wrote:
> The combination of KASAN_STACK and GCC_PLUGIN_STRUCTLEAK_BYREF
> leads to much larger kernel stack usage, as seen from the warnings
> about functions that now exceed the 2048 byte limit:
>
> drivers/media/i2c/tvp5150.c:253:1: error: the frame size of 3936 bytes is larger than 2048 bytes
> drivers/media/tuners/r820t.c:1327:1: error: the frame size of 2816 bytes is larger than 2048 bytes
> drivers/net/wireless/broadcom/brcm80211/brcmsmac/phy/phy_n.c:16552:1: error: the frame size of 3144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> fs/ocfs2/aops.c:1892:1: error: the frame size of 2088 bytes is larger than 2048 bytes
> fs/ocfs2/dlm/dlmrecovery.c:737:1: error: the frame size of 2088 bytes is larger than 2048 bytes
> fs/ocfs2/namei.c:1677:1: error: the frame size of 2584 bytes is larger than 2048 bytes
> fs/ocfs2/super.c:1186:1: error: the frame size of 2640 bytes is larger than 2048 bytes
> fs/ocfs2/xattr.c:3678:1: error: the frame size of 2176 bytes is larger than 2048 bytes
> net/bluetooth/l2cap_core.c:7056:1: error: the frame size of 2144 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]
> net/bluetooth/l2cap_core.c: In function 'l2cap_recv_frame':
> net/bridge/br_netlink.c:1505:1: error: the frame size of 2448 bytes is larger than 2048 bytes
> net/ieee802154/nl802154.c:548:1: error: the frame size of 2232 bytes is larger than 2048 bytes
> net/wireless/nl80211.c:1726:1: error: the frame size of 2224 bytes is larger than 2048 bytes
> net/wireless/nl80211.c:2357:1: error: the frame size of 4584 bytes is larger than 2048 bytes
> net/wireless/nl80211.c:5108:1: error: the frame size of 2760 bytes is larger than 2048 bytes
> net/wireless/nl80211.c:6472:1: error: the frame size of 2112 bytes is larger than 2048 bytes
>
> The structleak plugin was previously disabled for CONFIG_COMPILE_TEST,
> but meant we missed some bugs, so this time we should address them.
>
> The frame size warnings are distracting, and risking a kernel stack
> overflow is generally not beneficial to performance, so it may be best
> to disallow that particular combination. This can be done by turning
> off either one. I picked the dependency in GCC_PLUGIN_STRUCTLEAK_BYREF
> and GCC_PLUGIN_STRUCTLEAK_BYREF_ALL, as this option is designed to
> make uninitialized stack usage less harmful when enabled on its own,
> but it also prevents KASAN from detecting those cases in which it was
> in fact needed.
>
> KASAN_STACK is currently implied by KASAN on gcc, but could be made a
> user selectable option if we want to allow combining (non-stack) KASAN
> with GCC_PLUGIN_STRUCTLEAK_BYREF.
>
> Note that it would be possible to specifically address the files that
> print the warning, but presumably the overall stack usage is still
> significantly higher than in other configurations, so this would not
> address the full problem.
>
> I could not test this with CONFIG_INIT_STACK_ALL, which may or may not
> suffer from a similar problem.
>
> Fixes: 81a56f6dcd20 ("gcc-plugins: structleak: Generalize to all variable types")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kees Cook <keescook@chromium.org>
-Kees
> ---
> [v2] do it for both GCC_PLUGIN_STRUCTLEAK_BYREF and GCC_PLUGIN_STRUCTLEAK_BYREF_ALL.
> ---
> security/Kconfig.hardening | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/security/Kconfig.hardening b/security/Kconfig.hardening
> index a1ffe2eb4d5f..af4c979b38ee 100644
> --- a/security/Kconfig.hardening
> +++ b/security/Kconfig.hardening
> @@ -61,6 +61,7 @@ choice
> config GCC_PLUGIN_STRUCTLEAK_BYREF
> bool "zero-init structs passed by reference (strong)"
> depends on GCC_PLUGINS
> + depends on !(KASAN && KASAN_STACK=1)
> select GCC_PLUGIN_STRUCTLEAK
> help
> Zero-initialize any structures on the stack that may
> @@ -70,9 +71,15 @@ choice
> exposures, like CVE-2017-1000410:
> https://git.kernel.org/linus/06e7e776ca4d3654
>
> + As a side-effect, this keeps a lot of variables on the
> + stack that can otherwise be optimized out, so combining
> + this with CONFIG_KASAN_STACK can lead to a stack overflow
> + and is disallowed.
> +
> config GCC_PLUGIN_STRUCTLEAK_BYREF_ALL
> bool "zero-init anything passed by reference (very strong)"
> depends on GCC_PLUGINS
> + depends on !(KASAN && KASAN_STACK=1)
> select GCC_PLUGIN_STRUCTLEAK
> help
> Zero-initialize any stack variables that may be passed
> --
> 2.20.0
>
--
Kees Cook
prev parent reply other threads:[~2019-06-28 14:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-28 12:37 [PATCH 1/4] [v2] structleak: disable STRUCTLEAK_BYREF in combination with KASAN_STACK Arnd Bergmann
2019-06-28 12:37 ` [PATCH 2/4] lpfc: reduce stack size with CONFIG_GCC_PLUGIN_STRUCTLEAK_VERBOSE Arnd Bergmann
2019-06-28 18:57 ` James Smart
2019-07-12 0:47 ` Martin K. Petersen
2019-06-28 12:37 ` [PATCH 3/4] staging: rtl8712: reduce stack usage, again Arnd Bergmann
2019-06-28 19:52 ` Willem de Bruijn
2019-06-28 12:37 ` [PATCH 4/4] ipvs: reduce kernel stack usage Arnd Bergmann
2019-06-28 19:50 ` Willem de Bruijn
2019-07-22 10:28 ` Arnd Bergmann
2019-06-30 20:36 ` Julian Anastasov
2019-07-22 10:16 ` Arnd Bergmann
2019-06-28 14:48 ` Kees Cook [this message]
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