Re: [PATCH RFC v3 12/36] kmsan: define READ_ONCE_NOCHECK()

From: Alexander Potapenko <glider@google.com>
To: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Vegard Nossum <vegard.nossum@oracle.com>,
	 Dmitry Vyukov <dvyukov@google.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	 Al Viro <viro@zeniv.linux.org.uk>,
	Andreas Dilger <adilger.kernel@dilger.ca>,
	 Andrew Morton <akpm@linux-foundation.org>,
	Andrey Konovalov <andreyknvl@google.com>,
	 Andrey Ryabinin <aryabinin@virtuozzo.com>,
	Andy Lutomirski <luto@kernel.org>,
	 Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Arnd Bergmann <arnd@arndb.de>,
	 Christoph Hellwig <hch@infradead.org>,
	Christoph Hellwig <hch@lst.de>,
	 "Darrick J. Wong" <darrick.wong@oracle.com>,
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	 Thomas Gleixner <tglx@linutronix.de>,
	Vasily Gorbik <gor@linux.ibm.com>,
	Wolfram Sang <wsa@the-dreams.de>
Subject: Re: [PATCH RFC v3 12/36] kmsan: define READ_ONCE_NOCHECK()
Date: Tue, 3 Dec 2019 13:45:57 +0100	[thread overview]
Message-ID: <CAG_fn=VRzj3CgEnk86Az58271rYY++82aGBo2N=W4Zt7cjokRQ@mail.gmail.com> (raw)
In-Reply-To: <CANpmjNMr4Nrk5Pt-FjkF=OrKAckRx1+BJROKvpwGcc1Ay884uQ@mail.gmail.com>

On Mon, Dec 2, 2019 at 11:03 AM Marco Elver <elver@google.com> wrote:
>
> On Fri, 22 Nov 2019 at 12:27, <glider@google.com> wrote:
> >
> > READ_ONCE_NOCHECK() is already used by KASAN to ignore memory accesses
> > from e.g. stack unwinders.
> > Define READ_ONCE_NOCHECK() for KMSAN so that it returns initialized
> > values. This helps defeat false positives from leftover stack contents.
> >
> > Signed-off-by: Alexander Potapenko <glider@google.com>
> > To: Alexander Potapenko <glider@google.com>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: Vegard Nossum <vegard.nossum@oracle.com>
> > Cc: Dmitry Vyukov <dvyukov@google.com>
> > Cc: linux-mm@kvack.org
> > ---
> > v3:
> >  - removed unnecessary #ifdef as requested by Mark Rutland
> >
> > Change-Id: Ib38369ba038ab3b581d8e45b81036c3304fb79cb
> > ---
> >  include/linux/compiler.h | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/linux/compiler.h b/include/linux/compiler.h
> > index 5e88e7e33abe..99d40f31a2c3 100644
> > --- a/include/linux/compiler.h
> > +++ b/include/linux/compiler.h
> > @@ -270,9 +270,9 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
> >
> >  /*
> >   * Use READ_ONCE_NOCHECK() instead of READ_ONCE() if you need
> > - * to hide memory access from KASAN.
> > + * to hide memory access from KASAN or KMSAN.
> >   */
> > -#define READ_ONCE_NOCHECK(x) __READ_ONCE(x, 0)
> > +#define READ_ONCE_NOCHECK(x) KMSAN_INIT_VALUE(__READ_ONCE(x, 0))
>
> I think this needs:
>     #include <linux/kmsan-checks.h>
> above.
Ack, will include in v4.
> >  static __no_kasan_or_inline
> >  unsigned long read_word_at_a_time(const void *addr)
> > --
> > 2.24.0.432.g9d3f5f5b63-goog
> >


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Alexander Potapenko
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