x86/fault: Bypass no_context() for implicit kernel faults from usermode

Drop an indentation level and remove the last user_mode(regs) == true
caller of no_context() by directly OOPSing for implicit kernel faults
from usermode.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/6e3d1129494a8de1e59d28012286e3a292a2296e.1612924255.git.luto@kernel.org

arch/x86/mm/fault.c

@@ -826,9 +826,19 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 {
 	struct task_struct *tsk = current;
 
-	/* User mode accesses just cause a SIGSEGV */
-	if (user_mode(regs) && (error_code & X86_PF_USER)) {
+	if (!user_mode(regs)) {
+		no_context(regs, error_code, address, pkey, si_code);
+		return;
+	}
+
+	if (!(error_code & X86_PF_USER)) {
+		/* Implicit user access to kernel memory -- just oops */
+		page_fault_oops(regs, error_code, address);
+		return;
+	}
+
 	/*
+	 * User mode accesses just cause a SIGSEGV.
 	 * It's possible to have interrupts off here:
 	 */
 	local_irq_enable();
@@ -859,11 +869,6 @@ __bad_area_nosemaphore(struct pt_regs *regs, unsigned long error_code,
 	force_sig_fault(SIGSEGV, si_code, (void __user *)address);
 
 	local_irq_disable();
-
-		return;
-	}
-
-	no_context(regs, error_code, address, SIGSEGV, si_code);
 }
 
 static noinline void