ARM: 8148/1: flush TLS and thumbee register state during exec

The TPIDRURO and TPIDRURW registers need to be flushed during exec;
otherwise TLS information is potentially leaked.  TPIDRURO in
particular needs careful treatment.  Since flush_thread basically
needs the same code used to set the TLS in arm_syscall, pull that into
a common set_tls helper in tls.h and use it in both places.

Similarly, TEEHBR needs to be cleared during exec as well.  Clearing
its save slot in thread_info isn't right as there is no guarantee
that a thread switch will occur before the new program runs.  Just
setting the register directly is sufficient.

Signed-off-by: Nathan Lynch <[email protected]>
Acked-by: Will Deacon <[email protected]>
Cc: <[email protected]>
Signed-off-by: Russell King <[email protected]>

Author: nlynch-mentor

arch/arm/include/asm/tls.h

@@ -1,6 +1,9 @@
 #ifndef __ASMARM_TLS_H
 #define __ASMARM_TLS_H
 
+#include <linux/compiler.h>
+#include <asm/thread_info.h>
+
 #ifdef __ASSEMBLY__
 #include <asm/asm-offsets.h>
 	.macro switch_tls_none, base, tp, tpuser, tmp1, tmp2
@@ -50,6 +53,47 @@
 #endif
 
 #ifndef __ASSEMBLY__
+
+static inline void set_tls(unsigned long val)
+{
+	struct thread_info *thread;
+
+	thread = current_thread_info();
+
+	thread->tp_value[0] = val;
+
+	/*
+	 * This code runs with preemption enabled and therefore must
+	 * be reentrant with respect to switch_tls.
+	 *
+	 * We need to ensure ordering between the shadow state and the
+	 * hardware state, so that we don't corrupt the hardware state
+	 * with a stale shadow state during context switch.
+	 *
+	 * If we're preempted here, switch_tls will load TPIDRURO from
+	 * thread_info upon resuming execution and the following mcr
+	 * is merely redundant.
+	 */
+	barrier();
+
+	if (!tls_emu) {
+		if (has_tls_reg) {
+			asm("mcr p15, 0, %0, c13, c0, 3"
+			    : : "r" (val));
+		} else {
+			/*
+			 * User space must never try to access this
+			 * directly.  Expect your app to break
+			 * eventually if you do so.  The user helper
+			 * at 0xffff0fe0 must be used instead.  (see
+			 * entry-armv.S for details)
+			 */
+			*((unsigned int *)0xffff0ff0) = val;
+		}
+
+	}
+}
+
 static inline unsigned long get_tpuser(void)
 {
 	unsigned long reg = 0;
@@ -59,5 +103,23 @@ static inline unsigned long get_tpuser(void)
 
 	return reg;
 }
+
+static inline void set_tpuser(unsigned long val)
+{
+	/* Since TPIDRURW is fully context-switched (unlike TPIDRURO),
+	 * we need not update thread_info.
+	 */
+	if (has_tls_reg && !tls_emu) {
+		asm("mcr p15, 0, %0, c13, c0, 2"
+		    : : "r" (val));
+	}
+}
+
+static inline void flush_tls(void)
+{
+	set_tls(0);
+	set_tpuser(0);
+}
+
 #endif
 #endif	/* __ASMARM_TLS_H */

arch/arm/kernel/process.c

@@ -334,6 +334,8 @@ void flush_thread(void)
 	memset(&tsk->thread.debug, 0, sizeof(struct debug_info));
 	memset(&thread->fpstate, 0, sizeof(union fp_state));
 
+	flush_tls();
+
 	thread_notify(THREAD_NOTIFY_FLUSH, thread);
 }
 

arch/arm/kernel/thumbee.c

@@ -45,7 +45,7 @@ static int thumbee_notifier(struct notifier_block *self, unsigned long cmd, void
 
 	switch (cmd) {
 	case THREAD_NOTIFY_FLUSH:
-		thread->thumbee_state = 0;
+		teehbr_write(0);
 		break;
 	case THREAD_NOTIFY_SWITCH:
 		current_thread_info()->thumbee_state = teehbr_read();

arch/arm/kernel/traps.c

@@ -581,7 +581,6 @@ do_cache_op(unsigned long start, unsigned long end, int flags)
 #define NR(x) ((__ARM_NR_##x) - __ARM_NR_BASE)
 asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 {
-	struct thread_info *thread = current_thread_info();
 	siginfo_t info;
 
 	if ((no >> 16) != (__ARM_NR_BASE>> 16))
@@ -632,21 +631,7 @@ asmlinkage int arm_syscall(int no, struct pt_regs *regs)
 		return regs->ARM_r0;
 
 	case NR(set_tls):
-		thread->tp_value[0] = regs->ARM_r0;
-		if (tls_emu)
-			return 0;
-		if (has_tls_reg) {
-			asm ("mcr p15, 0, %0, c13, c0, 3"
-				: : "r" (regs->ARM_r0));
-		} else {
-			/*
-			 * User space must never try to access this directly.
-			 * Expect your app to break eventually if you do so.
-			 * The user helper at 0xffff0fe0 must be used instead.
-			 * (see entry-armv.S for details)
-			 */
-			*((unsigned int *)0xffff0ff0) = regs->ARM_r0;
-		}
+		set_tls(regs->ARM_r0);
 		return 0;
 
 #ifdef CONFIG_NEEDS_SYSCALL_FOR_CMPXCHG