Re: [PATCH 0/2]: ARM: Enable THREAD_INFO_IN_TASK

From: "Russell King (Oracle)" <linux@armlinux.org.uk>
To: Keith Packard <keithp@keithp.com>
Cc: linux-kernel@vger.kernel.org,
	"Abbott Liu" <liuwenliang@huawei.com>,
	"Alexander Sverdlin" <alexander.sverdlin@gmail.com>,
	"Al Viro" <viro@zeniv.linux.org.uk>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Ard Biesheuvel" <ardb@kernel.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Bjorn Andersson" <bjorn.andersson@linaro.org>,
	"Florian Fainelli" <f.fainelli@gmail.com>,
	"Geert Uytterhoeven" <geert+renesas@glider.be>,
	"Hartley Sweeten" <hsweeten@visionengravers.com>,
	"Jens Axboe" <axboe@kernel.dk>, "Jian Cai" <jiancai@google.com>,
	"Joe Perches" <joe@perches.com>,
	"Linus Walleij" <linus.walleij@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	"Maninder Singh" <maninder1.s@samsung.com>,
	"Manivannan Sadhasivam" <mani@kernel.org>,
	"Marc Zyngier" <maz@kernel.org>,
	"Masahiro Yamada" <masahiroy@kernel.org>,
	"Mike Rapoport" <rppt@kernel.org>,
	"Nick Desaulniers" <ndesaulniers@google.com>,
	"Nick Desaulniers" <ndesaulniers@gooogle.com>,
	"Nicolas Pitre" <nico@fluxnic.net>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
	"Valentin Schneider" <valentin.schneider@arm.com>,
	"Vaneet Narang" <v.narang@samsung.com>,
	"Wolfram Sang (Renesas)" <wsa+renesas@sang-engineering.com>,
	"YiFei Zhu" <yifeifz2@illinois.edu>,
	"Keith Packard" <keithpac@amazon.com>
Subject: Re: [PATCH 0/2]: ARM: Enable THREAD_INFO_IN_TASK
Date: Thu, 2 Sep 2021 17:53:53 +0100	[thread overview]
Message-ID: <20210902165353.GI22278@shell.armlinux.org.uk> (raw)
In-Reply-To: <20210902155429.3987201-1-keithp@keithp.com>

On Thu, Sep 02, 2021 at 08:54:26AM -0700, Keith Packard wrote:
> Placing thread_info in the kernel stack leaves it vulnerable to stack
> overflow attacks. This short series addresses that by using the
> existing THREAD_INFO_IN_TASK infrastructure.
> 
> As this is my first patch in this part of the kernel, I'm looking for
> feedback about the general approach as well as specific comments on
> places where I've missed something.
> 
> I've only run this on armhf running under qemu, so while I've tried to
> make patches for other code paths, I haven't been able to test those.
> 
> (yes, I know checkpatch.pl complains about whitespace in asm-offsets.c, I
> decided to leave the existing whitespace alone)
> 
> Signed-off-by: Keith Packard <keithpac@amazon.com>

I think you're introducing a circular dependency with this for
certain kernel configurations:

E.g. Have you tried running this with CONFIG_CPU_V6 enabled?

+#define raw_smp_processor_id() this_cpu_read(cpu_number)
+#define __smp_processor_id() __this_cpu_read(cpu_number)
+
+DECLARE_PER_CPU_READ_MOSTLY(unsigned int, cpu_number);

this_cpu_read() is defined as:

#define this_cpu_read(pcp) __pcpu_size_call_return(this_cpu_read_, pcp)
(which will call this_cpu_read_4)

#define this_cpu_read_4(pcp)            this_cpu_generic_read(pcp)
=> __this_cpu_generic_read_nopreempt()
=>         ___ret = READ_ONCE(*raw_cpu_ptr(&(pcp)));

#define raw_cpu_ptr(ptr)                                                \
({                                                                      \
        __verify_pcpu_ptr(ptr);                                         \
        arch_raw_cpu_ptr(ptr);                                          \
})

#ifndef arch_raw_cpu_ptr
#define arch_raw_cpu_ptr(ptr) SHIFT_PERCPU_PTR(ptr, __my_cpu_offset)
#endif

#ifndef __my_cpu_offset
#define __my_cpu_offset per_cpu_offset(raw_smp_processor_id())
#endif

... which then leads back to a use of raw_smp_processor_id(), thereby
creating a circular loop of preprocessor definitions that the compiler
can't resolve.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel