Messages in this thread | | | From | Dmitry Vyukov <> | Date | Thu, 28 Feb 2019 11:05:10 +0100 | Subject | Re: [PATCH 5/6] objtool: Add UACCESS validation |
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On Thu, Feb 28, 2019 at 10:59 AM Dmitry Vyukov <dvyukov@google.com> wrote: > > On Thu, Feb 28, 2019 at 10:40 AM Peter Zijlstra <peterz@infradead.org> wrote: > > > > On Wed, Feb 27, 2019 at 06:28:16PM +0100, Peter Zijlstra wrote: > > > On Wed, Feb 27, 2019 at 04:40:28PM +0100, Dmitry Vyukov wrote: > > > > On Wed, Feb 27, 2019 at 3:33 PM Peter Zijlstra <peterz@infradead.org> wrote: > > > > > > > > Urgh, kasan_report() is definitely unsafe. Now, admitedly we should > > > > > 'never' hit that, but it does leave us up a creek without a paddle. > > > > > > > If SMAP detects additional bugs, then it would be pity to disable it > > > > with KASAN (detect bugs in production but not during testing). > > > > > > > > You mentioned that exception save/restore the UACCESS state. Is it > > > > possible to do the same in kasan_report? At the very least we need to > > > > survive report printing, what happens after that does not matter much > > > > (we've corrupted memory by now anyway). > > > > > > Ideally we'll put all of kasan_report() in an exception, much like we do > > > for WARN. But there's a distinct lack of arch hooks there to play with. > > > I suppose I can try and create some. > > > > > > On top of that we'll have to mark these __asan functions with notrace. > > > > > > Maybe a little something horrible like so... completely untested. > > > > OK, I got that to compile; the next problem is: > > > > ../include/linux/kasan.h:90:1: error: built-in function ‘__asan_loadN_noabort’ must be directly called > > UACCESS_SAFE(__asan_loadN_noabort); > > > > Which doesn't make any sense; since we actually generated that symbol, > > it clearly is not built-in. What gives? > > I guess this warning originated for user-space where programmer does > not define them and does not generally know about them and signature > is not a public contract for user. And then for kernel it just stayed > the same because not doing this warning would require somebody to > proactively think about this potential difference and add an > additional code to skip this check and even then it wasn't obvious why > one will want to do this with these functions. So that's where we are > now.
Maybe asm directive will help to trick the compiler?
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