linux-kernel - Re: [PATCH v2] mm: kmsan: remove runtime checks from kmsan_unpoison

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Message-Id: <20240125173448.e866d84cda146145cbc67c93@linux-foundation.org>
Date: Thu, 25 Jan 2024 17:34:48 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Alexander Potapenko <glider@...gle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 kasan-dev@...glegroups.com, Marco Elver <elver@...gle.com>, Dmitry Vyukov
 <dvyukov@...gle.com>, Ilya Leoshkevich <iii@...ux.ibm.com>, Nicholas
 Miehlbradt <nicholas@...ux.ibm.com>
Subject: Re: [PATCH v2] mm: kmsan: remove runtime checks from
 kmsan_unpoison_memory()

On Wed, 24 Jan 2024 18:31:34 +0100 Alexander Potapenko <glider@...gle.com> wrote:

> Similarly to what's been done in commit ff444efbbb9be ("kmsan: allow

I make that 85716a80c16d.

> using __msan_instrument_asm_store() inside runtime"), it should be safe
> to call kmsan_unpoison_memory() from within the runtime, as it does not
> allocate memory or take locks. Remove the redundant runtime checks.
> 
> This should fix false positives seen with CONFIG_DEBUG_LIST=y when
> the non-instrumented lib/stackdepot.c failed to unpoison the memory
> chunks later checked by the instrumented lib/list_debug.c
> 
> Also replace the implementation of kmsan_unpoison_entry_regs() with
> a call to kmsan_unpoison_memory().
> 

"false positives" sound unpleasant.  Should this fix be backported into
earlier kernels?  And can we identify a suitable Fixes: target?