openrisc: traps: Don't send signals to kernel mode threads

OpenRISC exception handling sends signals to user processes on floating
point exceptions and trap instructions (for debugging) among others.
There is a bug where the trap handling logic may send signals to kernel
threads, we should not send these signals to kernel threads, if that
happens we treat it as an error.

This patch adds conditions to die if the kernel receives these
exceptions in kernel mode code.

Fixes: 2726765 ("openrisc: Support floating point user api")
Signed-off-by: Stafford Horne <shorne@gmail.com>

Author: stffrdhrn

arch/openrisc/kernel/traps.c

@@ -180,29 +180,39 @@ asmlinkage void unhandled_exception(struct pt_regs *regs, int ea, int vector)
 
 asmlinkage void do_fpe_trap(struct pt_regs *regs, unsigned long address)
 {
-	int code = FPE_FLTUNK;
-	unsigned long fpcsr = regs->fpcsr;
-
-	if (fpcsr & SPR_FPCSR_IVF)
-		code = FPE_FLTINV;
-	else if (fpcsr & SPR_FPCSR_OVF)
-		code = FPE_FLTOVF;
-	else if (fpcsr & SPR_FPCSR_UNF)
-		code = FPE_FLTUND;
-	else if (fpcsr & SPR_FPCSR_DZF)
-		code = FPE_FLTDIV;
-	else if (fpcsr & SPR_FPCSR_IXF)
-		code = FPE_FLTRES;
-
-	/* Clear all flags */
-	regs->fpcsr &= ~SPR_FPCSR_ALLF;
-
-	force_sig_fault(SIGFPE, code, (void __user *)regs->pc);
+	if (user_mode(regs)) {
+		int code = FPE_FLTUNK;
+		unsigned long fpcsr = regs->fpcsr;
+
+		if (fpcsr & SPR_FPCSR_IVF)
+			code = FPE_FLTINV;
+		else if (fpcsr & SPR_FPCSR_OVF)
+			code = FPE_FLTOVF;
+		else if (fpcsr & SPR_FPCSR_UNF)
+			code = FPE_FLTUND;
+		else if (fpcsr & SPR_FPCSR_DZF)
+			code = FPE_FLTDIV;
+		else if (fpcsr & SPR_FPCSR_IXF)
+			code = FPE_FLTRES;
+
+		/* Clear all flags */
+		regs->fpcsr &= ~SPR_FPCSR_ALLF;
+
+		force_sig_fault(SIGFPE, code, (void __user *)regs->pc);
+	} else {
+		pr_emerg("KERNEL: Illegal fpe exception 0x%.8lx\n", regs->pc);
+		die("Die:", regs, SIGFPE);
+	}
 }
 
 asmlinkage void do_trap(struct pt_regs *regs, unsigned long address)
 {
-	force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->pc);
+	if (user_mode(regs)) {
+		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->pc);
+	} else {
+		pr_emerg("KERNEL: Illegal trap exception 0x%.8lx\n", regs->pc);
+		die("Die:", regs, SIGILL);
+	}
 }
 
 asmlinkage void do_unaligned_access(struct pt_regs *regs, unsigned long address)