Messages in this thread | | | From | Patricia Alfonso <> | Date | Thu, 6 Feb 2020 10:33:08 -0800 | Subject | Re: [RFC PATCH] UML: add support for KASAN under x86_64 |
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On Fri, Jan 17, 2020 at 2:05 AM Dmitry Vyukov <dvyukov@google.com> wrote: > > On Fri, Jan 17, 2020 at 11:03 AM Dmitry Vyukov <dvyukov@google.com> wrote: > > > > On Fri, Jan 17, 2020 at 10:59 AM Dmitry Vyukov <dvyukov@google.com> wrote: > > > > > > On Thu, Jan 16, 2020 at 10:39 PM Patricia Alfonso > > > <trishalfonso@google.com> wrote: > > > > > > > > On Thu, Jan 16, 2020 at 1:23 AM Dmitry Vyukov <dvyukov@google.com> wrote: > > > > > > > > > > On Thu, Jan 16, 2020 at 10:20 AM Johannes Berg > > > > > <johannes@sipsolutions.net> wrote: > > > > > > > > > > > > On Thu, 2020-01-16 at 10:18 +0100, Dmitry Vyukov wrote: > > > > > > > > > > > > > > This should resolve the problem with constructors (after they > > > > > > > initialize KASAN, they can proceed to do anything they need) and it > > > > > > > should get rid of most KASAN_SANITIZE (in particular, all of > > > > > > > lib/Makefile and kernel/Makefile) and should fix stack instrumentation > > > > > > > (in case it does not work now). The only tiny bit we should not > > > > > > > instrument is the path from constructor up to mmap call. > > > >
By initializing KASAN as the first thing that executes, I have been able to get rid of most of the "KASAN_SANITIZE := n" lines and I am very happy about that. Thanks for the suggestions!
> > > If that part of the code I mentioned is instrumented, manifestation > > > would be different -- stack instrumentation will try to access shadow, > > > shadow is not mapped yet, so it would crash on the shadow access. > > > > > > What you are seeing looks like, well, a kernel bug where it does a bad > > > stack access. Maybe it's KASAN actually _working_? :) > > > > Though, stack instrumentation may have issues with longjmp-like things. > > I would suggest first turning off stack instrumentation and getting > > that work. Solving problems one-by-one is always easier. > > If you need help debugging this, please post more info: patch, what > > you are doing, full kernel output (preferably from start, if it's not > > too lengthy). > > I see syscall_stub_data does some weird things with stack (stack > copy?). Maybe we just need to ignore accesses there: individual > accesses, or whole function/file.
It is still not clear whether the syscall_stub_data errors are false positives, but while moving the kasan_init() to be as early as possible in main(), I ran into a few more stack-related errors like this(show_stack, dump_trace, and get_wchan). I will be taking your advice to focus on one thing at a time and temporarily disable stack instrumentation wherever possible.
-- Patricia Alfonso
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