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Re: [Public WebGL] Proposals for two new WebGL extensions




On 05/10/11 03:56 PM, Gregg Tavares (wrk) wrote:


On Wed, Oct 5, 2011 at 12:08 PM, Benoit Jacob <bjacob@mozilla.com
<mailto:bjacob@mozilla.com>> wrote:


On 05/10/11 02:38 PM, Mo, Zhenyao wrote:

        I wrote up drafts for two possible WebGL extensions:
        WEBGL_debug_shaders
        and WEBGL_debug_gpu_info.

        https://cvs.khronos.org/svn/__repos/registry/trunk/public/__webgl/extensions/proposals/__WEBGL_debug_gpu_info.html
        <https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/extensions/proposals/WEBGL_debug_gpu_info.html>
        https://cvs.khronos.org/svn/__repos/registry/trunk/public/__webgl/extensions/proposals/__WEBGL_debug_shaders.html
        <https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/extensions/proposals/WEBGL_debug_shaders.html>

        WEBGL_debug_shaders exposes the translated shader source.
        WEBGL_debug_gpu_info exposes the unmasked VENDOR and RENDERER
        strings
        from underlying graphics driver.

        I believe these two extensions provide important information to
        WebGL
        developers.  However, as stated in the drafts, both extensions
        should
        only be available to privileged code in a browser, not the regular
        content due to user privacy concerns.


I'm OK with the two extensions as currently drafted; just a couple of remarks:

      *WEBGL_debug_gpu_info might be better named
    WEBGL_debug_renderer_info (or see below,
    WEBGL_privileged_renderer___info) ? Also, it says that that info
    should not be exposed to unprivileged content, so should the WebGL
    spec also be updated to be consistent with that? Currently the WebGL
    spec does not mention the concern about these strings. Also, I
    wonder if PRIVILEGED would be a better word than UNMASKED, so it
    would tell in a more explicit and neutral way what the difference is
    with the current strings from the spec. Similarly, the extension
    might be better named WEBGL_privileged_renderer___info?

      * WEBGL_debug_shaders might not be a specific enough name? How
    about WEBGL_get_translated_shader___source or some such. The text
    says that this should not be exposed to unprivileged content because
    this could be used to identify the GPU. Personally, my concern is a
    bit different. I'm not that much concerned about this particular
    privacy issue as it doesn't seem to expose a lot more information
    than we already expose (through getShaderInfoLog + getParameter + UA
    string), and doesn't make it more convenient to obtain. What I'm
    more concerned with is that it exposes precisely which workarounds
    we use, so if an attacker was fuzzing our ANGLE workarounds to find
    corner cases where we miss a workaround, that could be handy.


How is that any different from today? If an attacker wants to find out which workarounds we use, at least for Firefox and Chrome they can just download the source and find out. Yes this makes it slightly easier, they don't have to compile themselves and add a single printf, but it doesn't expose anything they couldn't already get.

So that's true for the two browsers that currently ship WebGL enabled by default. How much is that something that we can rely on, as opposed to just an 'accident', I don't know. But it surely isn't my job to advocate security-by-obscurity so I won't push this point further :-)


Benoit




Cheers, Benoit


Comments are welcome.

        Mo



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