linux-kernel - Re: [PATCH 1/2] x86/insn: Fix some potential undefined behavior.

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Message-ID: <20201015100522.GZ2611@hirez.programming.kicks-ass.net>
Date:   Thu, 15 Oct 2020 12:05:22 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Ian Rogers <irogers@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        linux-kernel@...r.kernel.org,
        Adrian Hunter <adrian.hunter@...el.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Numfor Mbiziwo-Tiapo <nums@...gle.com>
Subject: Re: [PATCH 1/2] x86/insn: Fix some potential undefined behavior.

On Wed, Oct 14, 2020 at 11:21:47PM -0700, Ian Rogers wrote:
> From: Numfor Mbiziwo-Tiapo <nums@...gle.com>
> 
> If insn_init is given a NULL kaddr and 0 buflen then validate_next will
> perform arithmetic on NULL, add a guard to avoid this.

How is this a problem? NULL is (void *)0, you can do arithmetic on that
just fine.

Is UBSAN taking drugs again?

> Don't perform unaligned loads in __get_next and __peek_nbyte_next as
> these are forms of undefined behavior.

Fair enough; that could actually be a problem when we start to
cross-build this stuff. A RISC hosted version of the x86 decoder could
indeed trip this up.


But also, these are two changes in one patch.