x86/ptrace: Provide pt_regs helper for entry/exit

As a preparatory step for moving the syscall and interrupt entry/exit
handling into generic code, provide a pt_regs helper which retrieves the
interrupt state from pt_regs. This is required to check whether interrupts
are reenabled by return from interrupt/exception.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/20200722220520.258511584@linutronix.de

arch/x86/include/asm/ptrace.h

@@ -209,6 +209,11 @@ static inline void user_stack_pointer_set(struct pt_regs *regs,
 	regs->sp = val;
 }
 
+static __always_inline bool regs_irqs_disabled(struct pt_regs *regs)
+{
+	return !(regs->flags & X86_EFLAGS_IF);
+}
+
 /* Query offset/name of register from its name/offset */
 extern int regs_query_register_offset(const char *name);
 extern const char *regs_query_register_name(unsigned int offset);