linux-kernel - Re: [PATCH] gcc-plugins: Add structleak for more stack initialization

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Date:   Mon, 16 Jan 2017 20:30:29 +0100
From:   "PaX Team" <pageexec@...email.hu>
To:     Mark Rutland <mark.rutland@....com>
CC:     kernel-hardening@...ts.openwall.com,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        "AKASHI, Takahiro" <takahiro.akashi@...aro.org>,
        park jinbum <jinb.park7@...il.com>,
        Daniel Micay <danielmicay@...il.com>,
        linux-kernel@...r.kernel.org, spender@...ecurity.net
Subject: Re: [PATCH] gcc-plugins: Add structleak for more stack initialization

On 16 Jan 2017 at 15:24, Mark Rutland wrote:

> To me, it seems that the __user annotation can only be an indicator of
> an issue by chance. We have structures with __user pointers in structs
> that will never be copied to userspace, and conversely we have structs
> that don't contain a __user field, but will be copied to userspace.
> 
> Maybe it happens that structs in more complex systems are more likely to
> contain some __user pointer. Was that part of the rationale?

it's as i explained in an earlier email: we wanted to pattern match a
specific bug situation and this was the easiest way (as you can see,
the plugin's code is very simple, not much effort went into it).

> I wonder if there's any analysis we can do of data passing into
> copy_to_user() and friends. I guess we can't follow the data flow across
> compilation units, but we might be able to follow it well enough if we
> added a new attribute that described whether data was to be copied to
> userspace.

there're are all kinds of data flow analyses you can do within and even
across translation units (summary info a'la size overflow hash tables or
LTO). i never went into that direction because i think the security goal
can be achieved without the performance impact of forced initialization.