linux-kernel - Re: [PATCH AUTOSEL 5.4 10/13] kmsan: disable physical page merging in biovec

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Date:   Mon, 17 Oct 2022 17:22:33 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Sasha Levin <sashal@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Christoph Hellwig <hch@....de>,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Ilya Leoshkevich <iii@...ux.ibm.com>,
        Ingo Molnar <mingo@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Kees Cook <keescook@...omium.org>,
        Marco Elver <elver@...gle.com>,
        Mark Rutland <mark.rutland@....com>,
        Matthew Wilcox <willy@...radead.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Pekka Enberg <penberg@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Petr Mladek <pmladek@...e.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Vegard Nossum <vegard.nossum@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-block@...r.kernel.org
Subject: Re: [PATCH AUTOSEL 5.4 10/13] kmsan: disable physical page merging
 in biovec

On Mon, Oct 17, 2022 at 08:10:59PM -0400, Sasha Levin wrote:
> From: Alexander Potapenko <glider@...gle.com>
> 
> [ Upstream commit f630a5d0ca59a6e73b61e3f82c371dc230da99ff ]
> 
> KMSAN metadata for adjacent physical pages may not be adjacent, therefore
> accessing such pages together may lead to metadata corruption.  We disable
> merging pages in biovec to prevent such corruptions.
> 
> Link: https://lkml.kernel.org/r/20220915150417.722975-28-glider@google.com
> Signed-off-by: Alexander Potapenko <glider@...gle.com>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Alexei Starovoitov <ast@...nel.org>
> Cc: Andrey Konovalov <andreyknvl@...il.com>
> Cc: Andrey Konovalov <andreyknvl@...gle.com>
> Cc: Andy Lutomirski <luto@...nel.org>
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: David Rientjes <rientjes@...gle.com>
> Cc: Dmitry Vyukov <dvyukov@...gle.com>
> Cc: Eric Biggers <ebiggers@...gle.com>
> Cc: Eric Biggers <ebiggers@...nel.org>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: Ilya Leoshkevich <iii@...ux.ibm.com>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Joonsoo Kim <iamjoonsoo.kim@....com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Marco Elver <elver@...gle.com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Michael S. Tsirkin <mst@...hat.com>
> Cc: Pekka Enberg <penberg@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Vasily Gorbik <gor@...ux.ibm.com>
> Cc: Vegard Nossum <vegard.nossum@...cle.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  block/blk.h | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/block/blk.h b/block/blk.h
> index ee3d5664d962..3358ef4244fe 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -79,6 +79,13 @@ static inline bool biovec_phys_mergeable(struct request_queue *q,
>  	phys_addr_t addr1 = page_to_phys(vec1->bv_page) + vec1->bv_offset;
>  	phys_addr_t addr2 = page_to_phys(vec2->bv_page) + vec2->bv_offset;
>  
> +	/*
> +	 * Merging adjacent physical pages may not work correctly under KMSAN
> +	 * if their metadata pages aren't adjacent. Just disable merging.
> +	 */
> +	if (IS_ENABLED(CONFIG_KMSAN))
> +		return false;
> +
>  	if (addr1 + vec1->bv_len != addr2)
>  		return false;
>  	if (xen_domain() && !xen_biovec_phys_mergeable(vec1, vec2->bv_page))

So KMSAN is being backported to 5.4?

- Eric