linux-kernel - Re: [PATCH 5/5] x86/traps: avoid KMSAN bugs originating from handle

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Date:   Wed, 2 Nov 2022 14:37:19 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org
Subject: Re: [PATCH 5/5] x86/traps: avoid KMSAN bugs originating from handle_bug()

On Wed, Nov 2, 2022 at 1:51 PM Peter Zijlstra <peterz@...radead.org> wrote:
>
> On Wed, Nov 02, 2022 at 12:06:11PM +0100, Alexander Potapenko wrote:
> > There is a case in exc_invalid_op handler that is executed outside the
> > irqentry_enter()/irqentry_exit() region when an UD2 instruction is used
> > to encode a call to __warn().
> >
> > In that case the `struct pt_regs` passed to the interrupt handler is
> > never unpoisoned by KMSAN (this is normally done in irqentry_enter()),
> > which leads to false positives inside handle_bug().
> >
> > Use kmsan_unpoison_entry_regs() to explicitly unpoison those registers
> > before using them.
>
> As does poke_int3_handler(); does that need fixing up too? OTOH look
> *very very* carefully at the contraints there.

Fortunately poke_int3_handler() is a noinstr function, so KMSAN
doesn't add any checks to it.
It also does not pass regs to other instrumented functions, at least
for now, so we're good.


-- 
Alexander Potapenko
Software Engineer

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