linux-kernel - Re: [PATCH 5.10 043/104] kasan: add explicit preconditions to kasan

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Date:   Tue, 16 Feb 2021 12:50:29 +0100
From:   Pavel Machek <pavel@....cz>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Leon Romanovsky <leonro@...lanox.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Naresh Kamboju <naresh.kamboju@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 5.10 043/104] kasan: add explicit preconditions to
 kasan_report()

Hi!

> From: Vincenzo Frascino <vincenzo.frascino@....com>
> 
> [ Upstream commit 49c6631d3b4f61a7b5bb0453a885a12bfa06ffd8 ]
> 
> Patch series "kasan: Fix metadata detection for KASAN_HW_TAGS", v5.
> 
> With the introduction of KASAN_HW_TAGS, kasan_report() currently assumes
> that every location in memory has valid metadata associated.  This is
> due to the fact that addr_has_metadata() returns always true.
> 
> As a consequence of this, an invalid address (e.g.  NULL pointer
> address) passed to kasan_report() when KASAN_HW_TAGS is enabled, leads
> to a kernel panic.
...
> This patch (of 2):
> 
> With the introduction of KASAN_HW_TAGS, kasan_report() accesses the
> metadata only when addr_has_metadata() succeeds.
> 
> Add a comment to make sure that the preconditions to the function are
> explicitly clarified.

As the other patch from the series is not applied, I don't believe we
need this in stable. Changelog does not make any sense with just
comment change cherry-picked...

Best regards,
								Pavel


> +++ b/include/linux/kasan.h
> @@ -196,6 +196,13 @@ void kasan_init_tags(void);
>  
>  void *kasan_reset_tag(const void *addr);
>  
> +/**
> + * kasan_report - print a report about a bad memory access detected by KASAN
> + * @addr: address of the bad access
> + * @size: size of the bad access
> + * @is_write: whether the bad access is a write or a read
> + * @ip: instruction pointer for the accessibility check or the bad access itself
> + */
>  bool kasan_report(unsigned long addr, size_t size,
>  		bool is_write, unsigned long ip);
>  

-- 
http://www.livejournal.com/~pavelmachek

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