On Mon, May 8, 2017 at 1:48 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, May 08, 2017 at 04:06:35PM +0200, Jann Horn wrote: > >> I think Kees might be talking about >> https://bugs.chromium.org/p/project-zero/issues/detail?id=822, fixed in >> commit e6978e4bf181fb3b5f8cb6f71b4fe30fbf1b655c. The issue was that >> perf code that can run in pretty much any context called access_ok(). > > And that commit has *NOT* solved the problem. perf_callchain_user() > can be called synchronously, without passing through that code. > Tracepoint shite... > > That set_fs() should be done in get_perf_callchain(), just around the call of > perf_callchain_user(). Along with pagefault_disable(), actually. > Even that's not quite enough because of a different issue: perf nmis can hit during scheduling or when we're in lazy mm, leading to the entirely wrong set of page tables being used. We need nmi_uaccess_begin() and nmi_uaccess_end(), and the former needs to be allowed to fail. AFAIK this isn't presently a security problem because it mainly affects kernel threads, and you need to be root to profile them, but maybe there's some race where it does matter. -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
