xtensa: fix signal delivery to FDPIC process

Fetch function descriptor pointed to by the signal handler pointer from
userspace on signal delivery and function pointer pointed to by the
sa_restorer on return from the signal handler.

Cc: stable@vger.kernel.org
Fixes: e3ddb8b ("xtensa: add FDPIC and static PIE support for noMMU")
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/signal.c

@@ -343,7 +343,19 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 	struct rt_sigframe *frame;
 	int err = 0, sig = ksig->sig;
 	unsigned long sp, ra, tp, ps;
+	unsigned long handler = (unsigned long)ksig->ka.sa.sa_handler;
+	unsigned long handler_fdpic_GOT = 0;
 	unsigned int base;
+	bool fdpic = IS_ENABLED(CONFIG_BINFMT_ELF_FDPIC) &&
+		(current->personality & FDPIC_FUNCPTRS);
+
+	if (fdpic) {
+		unsigned long __user *fdpic_func_desc =
+			(unsigned long __user *)handler;
+		if (__get_user(handler, &fdpic_func_desc[0]) ||
+		    __get_user(handler_fdpic_GOT, &fdpic_func_desc[1]))
+			return -EFAULT;
+	}
 
 	sp = regs->areg[1];
 
@@ -373,29 +385,34 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 	err |= __copy_to_user(&frame->uc.uc_sigmask, set, sizeof(*set));
 
 	if (ksig->ka.sa.sa_flags & SA_RESTORER) {
-		ra = (unsigned long)ksig->ka.sa.sa_restorer;
+		if (fdpic) {
+			unsigned long __user *fdpic_func_desc =
+				(unsigned long __user *)ksig->ka.sa.sa_restorer;
+
+			err |= __get_user(ra, fdpic_func_desc);
+		} else {
+			ra = (unsigned long)ksig->ka.sa.sa_restorer;
+		}
 	} else {
 
 		/* Create sys_rt_sigreturn syscall in stack frame */
 
 		err |= gen_return_code(frame->retcode);
-
-		if (err) {
-			return -EFAULT;
-		}
 		ra = (unsigned long) frame->retcode;
 	}
 
-	/* 
+	if (err)
+		return -EFAULT;
+
+	/*
 	 * Create signal handler execution context.
 	 * Return context not modified until this point.
 	 */
 
 	/* Set up registers for signal handler; preserve the threadptr */
 	tp = regs->threadptr;
 	ps = regs->ps;
-	start_thread(regs, (unsigned long) ksig->ka.sa.sa_handler,
-		     (unsigned long) frame);
+	start_thread(regs, handler, (unsigned long)frame);
 
 	/* Set up a stack frame for a call4 if userspace uses windowed ABI */
 	if (ps & PS_WOE_MASK) {
@@ -413,6 +430,8 @@ static int setup_frame(struct ksignal *ksig, sigset_t *set,
 	regs->areg[base + 4] = (unsigned long) &frame->uc;
 	regs->threadptr = tp;
 	regs->ps = ps;
+	if (fdpic)
+		regs->areg[base + 11] = handler_fdpic_GOT;
 
 	pr_debug("SIG rt deliver (%s:%d): signal=%d sp=%p pc=%08lx\n",
 		 current->comm, current->pid, sig, frame, regs->pc);