x86/traps: Make interrupt enable/disable symmetric in C code

Traps enable interrupts conditionally but rely on the ASM return code to
disable them again. That results in redundant interrupt disable and trace
calls.

Make the trap handlers disable interrupts before returning to avoid that,
which allows simplification of the ASM entry code in follow up changes.
Originally-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lkml.kernel.org/r/20200505134903.622702796@linutronix.de

arch/x86/kernel/traps.c

@@ -201,6 +201,7 @@ static void do_error_trap(struct pt_regs *regs, long error_code, char *str,
 			NOTIFY_STOP) {
 		cond_local_irq_enable(regs);
 		do_trap(trapnr, signr, str, regs, error_code, sicode, addr);
+		cond_local_irq_disable(regs);
 	}
 }
 
@@ -397,6 +398,8 @@ dotraplinkage void do_bounds(struct pt_regs *regs, long error_code)
 		die("bounds", regs, error_code);
 
 	do_trap(X86_TRAP_BR, SIGSEGV, "bounds", regs, error_code, 0, NULL);
+
+	cond_local_irq_disable(regs);
 }
 
 enum kernel_gp_hint {
@@ -456,12 +459,13 @@ dotraplinkage void do_general_protection(struct pt_regs *regs, long error_code)
 
 	if (static_cpu_has(X86_FEATURE_UMIP)) {
 		if (user_mode(regs) && fixup_umip_exception(regs))
-			return;
+			goto exit;
 	}
 
 	if (v8086_mode(regs)) {
 		local_irq_enable();
 		handle_vm86_fault((struct kernel_vm86_regs *) regs, error_code);
+		local_irq_disable();
 		return;
 	}
 
@@ -473,12 +477,11 @@ dotraplinkage void do_general_protection(struct pt_regs *regs, long error_code)
 
 		show_signal(tsk, SIGSEGV, "", desc, regs, error_code);
 		force_sig(SIGSEGV);
-
-		return;
+		goto exit;
 	}
 
 	if (fixup_exception(regs, X86_TRAP_GP, error_code, 0))
-		return;
+		goto exit;
 
 	tsk->thread.error_code = error_code;
 	tsk->thread.trap_nr = X86_TRAP_GP;
@@ -490,11 +493,11 @@ dotraplinkage void do_general_protection(struct pt_regs *regs, long error_code)
 	if (!preemptible() &&
 	    kprobe_running() &&
 	    kprobe_fault_handler(regs, X86_TRAP_GP))
-		return;
+		goto exit;
 
 	ret = notify_die(DIE_GPF, desc, regs, error_code, X86_TRAP_GP, SIGSEGV);
 	if (ret == NOTIFY_STOP)
-		return;
+		goto exit;
 
 	if (error_code)
 		snprintf(desc, sizeof(desc), "segment-related " GPFSTR);
@@ -516,6 +519,8 @@ dotraplinkage void do_general_protection(struct pt_regs *regs, long error_code)
 
 	die_addr(desc, regs, error_code, gp_addr);
 
+exit:
+	cond_local_irq_disable(regs);
 }
 NOKPROBE_SYMBOL(do_general_protection);
 
@@ -773,7 +778,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 
 	if (!user_mode(regs)) {
 		if (fixup_exception(regs, trapnr, error_code, 0))
-			return;
+			goto exit;
 
 		task->thread.error_code = error_code;
 		task->thread.trap_nr = trapnr;
@@ -781,7 +786,7 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 		if (notify_die(DIE_TRAP, str, regs, error_code,
 					trapnr, SIGFPE) != NOTIFY_STOP)
 			die(str, regs, error_code);
-		return;
+		goto exit;
 	}
 
 	/*
@@ -795,10 +800,12 @@ static void math_error(struct pt_regs *regs, int error_code, int trapnr)
 	si_code = fpu__exception_code(fpu, trapnr);
 	/* Retry when we get spurious exceptions: */
 	if (!si_code)
-		return;
+		goto exit;
 
 	force_sig_fault(SIGFPE, si_code,
 			(void __user *)uprobe_get_trap_addr(regs));
+exit:
+	cond_local_irq_disable(regs);
 }
 
 dotraplinkage void do_coprocessor_error(struct pt_regs *regs, long error_code)
@@ -853,6 +860,8 @@ do_device_not_available(struct pt_regs *regs, long error_code)
 
 		info.regs = regs;
 		math_emulate(&info);
+
+		cond_local_irq_disable(regs);
 		return;
 	}
 #endif
@@ -883,6 +892,7 @@ dotraplinkage void do_iret_error(struct pt_regs *regs, long error_code)
 		do_trap(X86_TRAP_IRET, SIGILL, "iret exception", regs, error_code,
 			ILL_BADSTK, (void __user *)NULL);
 	}
+	local_irq_disable();
 }
 #endif
 

arch/x86/mm/fault.c

@@ -786,6 +786,8 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 
 		force_sig_fault(SIGSEGV, si_code, (void __user *)address);
 
+		local_irq_disable();
+
 		return;
 	}
 
@@ -1384,9 +1386,18 @@ do_page_fault(struct pt_regs *regs, unsigned long hw_error_code,
 		return;
 
 	/* Was the fault on kernel-controlled part of the address space? */
-	if (unlikely(fault_in_kernel_space(address)))
+	if (unlikely(fault_in_kernel_space(address))) {
 		do_kern_addr_fault(regs, hw_error_code, address);
-	else
+	} else {
 		do_user_addr_fault(regs, hw_error_code, address);
+		/*
+		 * User address page fault handling might have reenabled
+		 * interrupts. Fixing up all potential exit points of
+		 * do_user_addr_fault() and its leaf functions is just not
+		 * doable w/o creating an unholy mess or turning the code
+		 * upside down.
+		 */
+		local_irq_disable();
+	}
 }
 NOKPROBE_SYMBOL(do_page_fault);