linux-hardening - Re: [PATCH v3 0/3] Assorted improvements to usercopy

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Date:   Mon, 13 Dec 2021 20:53:42 +0000
From:   William Kucharski <william.kucharski@...cle.com>
To:     Kees Cook <keescook@...omium.org>
CC:     Matthew Wilcox <willy@...radead.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] Assorted improvements to usercopy

Thanks, good explanation.

> On Dec 13, 2021, at 1:47 PM, Kees Cook <keescook@...omium.org> wrote:
> 
> On Mon, Dec 13, 2021 at 08:27:42PM +0000, Matthew Wilcox wrote:
>> On Mon, Dec 13, 2021 at 07:18:57PM +0000, William Kucharski wrote:
>>> I like these, but a quick question:
>>> 
>>> Since the usercopy_abort() calls are all because the offset exceeds the page
>>> size, is there a reason why you don't specifically state that via the detail
>>> parameter rather than just supply a NULL pointer?
>> 
>> Hmm ... I'd defer to Kees on this, because I'm not familiar with
>> usercopy_abort() usage, but the only places which use the detail
>> parameter today are slab/slub, which use it to pass the name of
>> the slab.  I think the user is supposed to infer that we overran the
>> end of the page based on the offset & length values.
> 
> I agree that leaving it NULL is best here. The "detail" is really about
> adding more information about which thing it was, which for slab makes
> sense, but most other stuff there isn't really anything to quickly
> distinguish one from another (i.e. vmap is all vmap).
> 
> -- 
> Kees Cook