On Tue, 26 Feb 2019 16:38:50 -0500 Joel Fernandes <j...@joelfernandes.org> wrote:
> On Mon, Feb 25, 2019 at 11:04:42PM +0900, Masami Hiramatsu wrote: > > Note that kprobe event provides these methods, but it doesn't > > change it from kernel to user automatically because we do not > > know whether the given address is in userspace or kernel on > > some arch. > > Moreover, from perf-probe, at this moment it is not able to > > switch. Since __user is not for compiler but checker, we have > > no clue which data structure is in user-space, in debuginfo. > > > > BTW, according to Linus's comment, I implemented probe_user_read() > > and strncpy_from_unsafe_user() APIs. And since those use > > "access_ok()" inside it, if CONFIG_DEBUG_ATOMIC_SLEEP=y on x86, > > it will get a warn message at once. It should be solved before > > merging this series. > > I was wondering why access_ok() can sleep. In the arm64 and x86 > implementation, I don't see access_ok() itself causing a user pointer > dereference access that can cause a page fault. It seems to just be checking > the validity of the ranges. > > Any idea why the access_ok() code has these comments? > "Context: User context only. This function may sleep if pagefaults are > enabled." Because access_ok() is used only for preparing accessing user-space, and the user-space access may cause page-fault and sleep. IMHO, checking in access_ok() inside it is reasonable, but as it commented, it is for "if pagefaults are enabled.". What we need another access_ok() for the case when pagefaults are disabled, that is what PeterZ suggested in below mail. https://lore.kernel.org/lkml/20190225150603.ge32...@hirez.programming.kicks-ass.net/T/#u Thank you, > > My _guess_ is this is because whatever calls access_ok() may also call > something else that *does* fault next, if that's the case then that > WARN_ON_IN_IRQ() in access_ok() is fine, but at least I guess the comments > should be more clear that it is not access_ok() itself that sleeps. > > thanks for any help on understanding this, > > - Joel > > > > > > Thank you, > > > > --- > > > > Masami Hiramatsu (4): > > uaccess: Make sure kernel_uaccess_faults_ok is updated before > > pagefault > > uaccess: Add non-pagefault user-space read functions > > tracing/probe: Add ustring type for user-space string > > tracing/probe: Support user-space dereference > > > > > > Documentation/trace/kprobetrace.rst | 13 ++- > > Documentation/trace/uprobetracer.rst | 9 +- > > fs/namespace.c | 2 > > include/linux/uaccess.h | 13 +++ > > kernel/trace/trace.c | 7 +- > > kernel/trace/trace_kprobe.c | 65 ++++++++++++++++ > > kernel/trace/trace_probe.c | 39 ++++++++-- > > kernel/trace/trace_probe.h | 3 + > > kernel/trace/trace_probe_tmpl.h | 36 +++++++-- > > kernel/trace/trace_uprobe.c | 19 +++++ > > mm/maccess.c | 138 > > ++++++++++++++++++++++++++++++---- > > 11 files changed, 302 insertions(+), 42 deletions(-) > > > > -- > > Masami Hiramatsu (Linaro) <mhira...@kernel.org> -- Masami Hiramatsu <mhira...@kernel.org>
