sh: sanitize the flags on sigreturn

We fetch %SR value from sigframe; it might have been modified by signal
handler, so we can't trust it with any bits that are not modifiable in
user mode.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Cc: Rich Felker <dalias@libc.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/sh/include/asm/processor_32.h

@@ -50,6 +50,7 @@
 #define SR_FD		0x00008000
 #define SR_MD		0x40000000
 
+#define SR_USER_MASK	0x00000303	// M, Q, S, T bits
 /*
  * DSP structure and data
  */

arch/sh/kernel/signal_32.c

@@ -115,6 +115,7 @@ static int
 restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, int *r0_p)
 {
 	unsigned int err = 0;
+	unsigned int sr = regs->sr & ~SR_USER_MASK;
 
 #define COPY(x)		err |= __get_user(regs->x, &sc->sc_##x)
 			COPY(regs[1]);
@@ -130,6 +131,8 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc, int *r0_p
 	COPY(sr);	COPY(pc);
 #undef COPY
 
+	regs->sr = (regs->sr & SR_USER_MASK) | sr;
+
 #ifdef CONFIG_SH_FPU
 	if (boot_cpu_data.flags & CPU_HAS_FPU) {
 		int owned_fp;