Re: [webkit-dev] Timing attacks on CSS Shaders (was Re:Security problems with CSS shaders)
On Fri, Dec 9, 2011 at 2:40 PM, Vincent Hardy vha...@adobe.com wrote: On Dec 7, 2011, at 7:29 PM, Adam Barth wrote: On Wed, Dec 7, 2011 at 7:23 PM, Vincent Hardy vha...@adobe.com wrote: @chris So I take back my statement that CSS Shaders are less dangerous than WebGL. They are more!!! It seems to me that the differences are: a. It is easier to do the timing portion of a timing attack in WebGL because it all happens in a script and the timing is precise. With CSS shaders, the timing is pretty coarse. b. The content that a CSS shader has access to may be more sensitive than the content a WebGL shader has access to because currently, WebGL cannot render HTML (but isn't it possible to render an SVG with a foreignObject containing HTML into a 2D canvas, and then use that as a texture? In that case, wouldn't the risk be the same? Or is the canvas tainted in that case and cannot be used as a texture?). Bear in mind that these security problems have been addressed in WebGL. WebGL no long suffers from these vulnerabilities. Yes, I understand WebGL now assumes CORS for allowing/disallowing access to resources. But my point was to clarify what is possible in terms of timing and what is possible (or may become possible) in terms of rendering. Timing on CSS shaders is coarse (because there is not precise way to time how long rendering of the shader takes unlike in WebGL). The attacker would rely on requestAnimationFrame, and the time that is measured with that method includes other processing than just the shader. So the timing measure is rough. It is definitely important that we protect against the threat, but my point is that the time measure is not great. @charles Can this proposal be moved forward on CORS + HTMLMediaElement, HTMLImageElement and HTMLCanvasElement? At the last FX meeting, I got an action to sync. up with the CORS group and discuss how CORS would apply to CSS shaders. It's very unclear to me how CORS can help in this situation. Can you explain what you have in mind? When a shader that applies to an element comes from a different origin than the rendered content, then rendering of the element would be blanked. The shader origin would be the shader's own url, the url of the page it is embedded in or the url of the script that created it dynamically (e.g., by injecting one dynamically with data: url for example, something Dean just mentioned to me in a conversation we had). If there is any mismatch between the origin of the shader and the origin of the shaded content, then the rendering would be blanked (unless CORS on the shaded content gives permission to the shader's origin). This would be done recursively on the content. It is unclear to me if any mismatch should blank out the whole rendering or if only the nodes in the tree that do not match should be blanked. As discussed previously, this approach is insufficient because some sensitive data is unrelated to cross-origin resources. For example, the color of hyperlinks is sensitive data but is unrelated to cross-origin resources, as is information displayed by the file upload control. The action item is to discuss this with the WebApps group. I agree that either the WebApps working group or the FX task force is the best place to discuss this topic. I've already started a thread on the FX task force mailing list, if you'd like to continue the discussion there. If you prefer the WebApps working group, please feel free to start a thread on public-webapps. Thanks, Adam ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
Re: [webkit-dev] Timing attacks on CSS Shaders (was Re:Security problems with CSS shaders)
From: Adam Barth aba...@webkit.orgmailto:aba...@webkit.org Date: Sat, 10 Dec 2011 00:34:42 -0800 To: Adobe Systems vha...@adobe.commailto:vha...@adobe.com Cc: webkit-dev@lists.webkit.orgmailto:webkit-dev@lists.webkit.org webkit-dev@lists.webkit.orgmailto:webkit-dev@lists.webkit.org Subject: Re: [webkit-dev] Timing attacks on CSS Shaders (was Re:Security problems with CSS shaders) On Fri, Dec 9, 2011 at 2:40 PM, Vincent Hardy vha...@adobe.commailto:vha...@adobe.com wrote: On Dec 7, 2011, at 7:29 PM, Adam Barth wrote: On Wed, Dec 7, 2011 at 7:23 PM, Vincent Hardy vha...@adobe.commailto:vha...@adobe.com wrote: @chris So I take back my statement that CSS Shaders are less dangerous than WebGL. They are more!!! It seems to me that the differences are: a. It is easier to do the timing portion of a timing attack in WebGL because it all happens in a script and the timing is precise. With CSS shaders, the timing is pretty coarse. b. The content that a CSS shader has access to may be more sensitive than the content a WebGL shader has access to because currently, WebGL cannot render HTML (but isn't it possible to render an SVG with a foreignObject containing HTML into a 2D canvas, and then use that as a texture? In that case, wouldn't the risk be the same? Or is the canvas tainted in that case and cannot be used as a texture?). Bear in mind that these security problems have been addressed in WebGL. WebGL no long suffers from these vulnerabilities. Yes, I understand WebGL now assumes CORS for allowing/disallowing access to resources. But my point was to clarify what is possible in terms of timing and what is possible (or may become possible) in terms of rendering. Timing on CSS shaders is coarse (because there is not precise way to time how long rendering of the shader takes unlike in WebGL). The attacker would rely on requestAnimationFrame, and the time that is measured with that method includes other processing than just the shader. So the timing measure is rough. It is definitely important that we protect against the threat, but my point is that the time measure is not great. @charles Can this proposal be moved forward on CORS + HTMLMediaElement, HTMLImageElement and HTMLCanvasElement? At the last FX meeting, I got an action to sync. up with the CORS group and discuss how CORS would apply to CSS shaders. It's very unclear to me how CORS can help in this situation. Can you explain what you have in mind? When a shader that applies to an element comes from a different origin than the rendered content, then rendering of the element would be blanked. The shader origin would be the shader's own url, the url of the page it is embedded in or the url of the script that created it dynamically (e.g., by injecting one dynamically with data: url for example, something Dean just mentioned to me in a conversation we had). If there is any mismatch between the origin of the shader and the origin of the shaded content, then the rendering would be blanked (unless CORS on the shaded content gives permission to the shader's origin). This would be done recursively on the content. It is unclear to me if any mismatch should blank out the whole rendering or if only the nodes in the tree that do not match should be blanked. As discussed previously, this approach is insufficient because some sensitive data is unrelated to cross-origin resources. For example, the color of hyperlinks is sensitive data but is unrelated to cross-origin resources, as is information displayed by the file upload control. Yes, I agree it is insufficient. But I think we agree that CORS is part of the solution. My understanding is that the defense could be built by mixing multiple protections. I think CORS can address the issue of getting access to pixels from a different domain, which is one of the problems we are trying to solve. The other issues you have raised, I think are generic to any solution (not just CSS shaders) where we might want to give access to the rendered HTML output (e.g., render an element or an HTML file in a canvas, for example). They also need to be addressed. The action item is to discuss this with the WebApps group. I agree that either the WebApps working group or the FX task force is the best place to discuss this topic. I've already started a thread on the FX task force mailing list, if you'd like to continue the discussion there. If you prefer the WebApps working group, please feel free to start a thread on public-webapps. Yes, I'll continue the discussion on public-fx. Dean is also preparing a summary of the issues which I think he will send there. Thanks, Vincent ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
[webkit-dev] Removing support for the RVCT compiler
Hola WebKittens! Are there any objections to removing support for the RVCT compiler (ARM RealView) in WebKit? As far as I know, the only user has been the Symbian port which is no longer present on WebKit trunk. -Kling ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
Re: [webkit-dev] Removing support for the RVCT compiler
On Sat, Dec 10, 2011 at 6:55 PM, Andreas Kling kl...@webkit.org wrote: Are there any objections to removing support for the RVCT compiler (ARM RealView) in WebKit? As far as I know, the only user has been the Symbian port which is no longer present on WebKit trunk. It looks like there are two usage of RVCT: Symbian and Linux. It would be interesting to have feedback on both. The Linux patches might still be used by someone. Cheers, Benjamin ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
Re: [webkit-dev] Removing support for the RVCT compiler
I'm curious what the practical implications of this are? Are there 500 #ifdefs for RVCT or 5? If it doesn't have a build bot, I'm sure it is broken anyway, and can just be removed regardless. :) -eric On Sat, Dec 10, 2011 at 7:24 PM, Benjamin Poulain benja...@webkit.org wrote: On Sat, Dec 10, 2011 at 6:55 PM, Andreas Kling kl...@webkit.org wrote: Are there any objections to removing support for the RVCT compiler (ARM RealView) in WebKit? As far as I know, the only user has been the Symbian port which is no longer present on WebKit trunk. It looks like there are two usage of RVCT: Symbian and Linux. It would be interesting to have feedback on both. The Linux patches might still be used by someone. Cheers, Benjamin ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
Re: [webkit-dev] Removing support for the RVCT compiler
On Sat, Dec 10, 2011 at 8:47 PM, Eric Seidel e...@webkit.org wrote: I'm curious what the practical implications of this are? Are there 500 #ifdefs for RVCT or 5? I think a dozen of #ifdef, plus a dozen of workarounds for compiler bugs. Benjamin ___ webkit-dev mailing list webkit-dev@lists.webkit.org http://lists.webkit.org/mailman/listinfo.cgi/webkit-dev
