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

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Message-ID: <Y2JnsG5QZoO4iazD@hirez.programming.kicks-ass.net>
Date:   Wed, 2 Nov 2022 13:50:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexander Potapenko <glider@...gle.com>
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 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.