powerpc/watchpoint/ptrace: Fix SETHWDEBUG when CONFIG_HAVE_HW_BREAKPOINT=N

When kernel is compiled with CONFIG_HAVE_HW_BREAKPOINT=N, user can
still create watchpoint using PPC_PTRACE_SETHWDEBUG, with limited
functionalities. But, such watchpoints are never firing because of
the missing privilege settings. Fix that.

It's safe to set HW_BRK_TYPE_PRIV_ALL because we don't really leak
any kernel address in signal info. Setting HW_BRK_TYPE_PRIV_ALL will
also help to find scenarios when kernel accesses user memory.

Reported-by: Pedro Miraglia Franco de Carvalho <pedromfc@linux.ibm.com>
Suggested-by: Pedro Miraglia Franco de Carvalho <pedromfc@linux.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200902042945.129369-4-ravi.bangoria@linux.ibm.com

arch/powerpc/kernel/ptrace/ptrace-noadv.c

@@ -217,7 +217,7 @@ long ppc_set_hwdebug(struct task_struct *child, struct ppc_hw_breakpoint *bp_inf
 		return -EIO;
 
 	brk.address = ALIGN_DOWN(bp_info->addr, HW_BREAKPOINT_SIZE);
-	brk.type = HW_BRK_TYPE_TRANSLATE;
+	brk.type = HW_BRK_TYPE_TRANSLATE | HW_BRK_TYPE_PRIV_ALL;
 	brk.len = DABR_MAX_LEN;
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_READ)
 		brk.type |= HW_BRK_TYPE_READ;