linux-kernel - Re: [PATCH v2 1/3] x86/uprobes: Fix not using prefixes.nbytes for loop over prefixes.bytes

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Message-ID: <20201203181712.GN3059@zn.tnic>
Date:   Thu, 3 Dec 2020 19:17:12 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Masami Hiramatsu <mhiramat@...nel.org>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "H . Peter Anvin" <hpa@...or.com>, Joerg Roedel <jroedel@...e.de>,
        "Gustavo A . R . Silva" <gustavoars@...nel.org>,
        Jann Horn <jannh@...gle.com>,
        Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] x86/uprobes: Fix not using prefixes.nbytes for
 loop over prefixes.bytes

On Thu, Dec 03, 2020 at 12:10:10PM -0600, Tom Lendacky wrote:
> Since that struct is used in multiple places, I think basing it on the array
> size is the best way to go. The main point of the check is just to be sure
> you don't read outside of the array.

Well, what happens if someone increases the array size of:

struct insn_field {
	union {
		insn_byte_t bytes[4];
				^^^^

?

That's why a separate array only for legacy prefixes would be better
in the long run. The array size check is good as a short-term fix for
stable.

I'd say.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette