powerpc/signal: Properly handle return value from uprobe_deny_signal()

[Michael Ellerman]

On Thu, 2017-08-31 at 16:25:57 UTC, "Naveen N. Rao" wrote:
> When a uprobe is installed on an instruction that we currently do not
> emulate, we copy the instruction into a xol buffer and single step
> that instruction. If that instruction generates a fault, we abort the
> single stepping before invoking the signal handler. Once the signal
> handler is done, the uprobe trap is hit again since the instruction is
> retried and the process repeats.
> 
> We use uprobe_deny_signal() to detect if the xol instruction triggered
> a signal. If so, we clear TIF_SIGPENDING and set TIF_UPROBE so that the
> signal is not handled until after the single stepping is aborted. In
> this case, uprobe_deny_signal() returns true and get_signal() ends up
> returning 0. However, in do_signal(), we are not looking at the return
> value, but depending on ksig.sig for further action, all with an
> uninitialized ksig that is not touched in this scenario. Fix the same
> by initializing ksig.sig to 0.
> 
> Fixes: 129b69df9c907 ("powerpc: Use get_signal() signal_setup_done()")
> 
> Reported-by: Anton Blanchard <anton at samba.org>
> Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/46725b17f1c6c815a41429259b3f07

cheers