MIPS: traps: return correct si code for accessing nonmapped addresses

find_vma() returns the first VMA which satisfies fault_addr < vm_end, but
it does not guarantee fault_addr is actually within VMA. Therefore, kernel
has to check that before it chooses correct si code on return.
Signed-off-by: NPetar Jovanovic <petar.jovanovic@rt-rk.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13808/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/kernel/traps.c

@@ -704,6 +704,7 @@ asmlinkage void do_ov(struct pt_regs *regs)
 int process_fpemu_return(int sig, void __user *fault_addr, unsigned long fcr31)
 {
 	struct siginfo si = { 0 };
+	struct vm_area_struct *vma;
 
 	switch (sig) {
 	case 0:
@@ -744,7 +745,8 @@ int process_fpemu_return(int sig, void __user *fault_addr, unsigned long fcr31)
 		si.si_addr = fault_addr;
 		si.si_signo = sig;
 		down_read(&current->mm->mmap_sem);
-		if (find_vma(current->mm, (unsigned long)fault_addr))
+		vma = find_vma(current->mm, (unsigned long)fault_addr);
+		if (vma && (vma->vm_start <= (unsigned long)fault_addr))
 			si.si_code = SEGV_ACCERR;
 		else
 			si.si_code = SEGV_MAPERR;