Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull address-limit checking fixes from Ingo Molnar:
"This fixes a number of bugs in the address-limit (USER_DS) checks that
got introduced in the merge window, (mostly) affecting the ARM and
ARM64 platforms"

* 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
arm64/syscalls: Move address limit check in loop
arm/syscalls: Optimize address limit check
Revert "arm/syscalls: Check address limit on user-mode return"
syscalls: Use CHECK_DATA_CORRUPTION for addr_limit_user_check

arch/arm/include/asm/thread_info.h

···
 #define TIF_NEED_RESCHED	1	/* rescheduling necessary */
 #define TIF_NOTIFY_RESUME	2	/* callback before returning to user */
 #define TIF_UPROBE		3	/* breakpointed or singlestepping */
-#define TIF_FSCHECK		4	/* Check FS is USER_DS on return */
-#define TIF_SYSCALL_TRACE	5	/* syscall trace active */
-#define TIF_SYSCALL_AUDIT	6	/* syscall auditing active */
-#define TIF_SYSCALL_TRACEPOINT	7	/* syscall tracepoint instrumentation */
-#define TIF_SECCOMP		8	/* seccomp syscall filtering active */
+#define TIF_SYSCALL_TRACE	4	/* syscall trace active */
+#define TIF_SYSCALL_AUDIT	5	/* syscall auditing active */
+#define TIF_SYSCALL_TRACEPOINT	6	/* syscall tracepoint instrumentation */
+#define TIF_SECCOMP		7	/* seccomp syscall filtering active */
 
 #define TIF_NOHZ		12	/* in adaptive nohz mode */
 #define TIF_USING_IWMMXT	17
···
 #define _TIF_NEED_RESCHED	(1 << TIF_NEED_RESCHED)
 #define _TIF_NOTIFY_RESUME	(1 << TIF_NOTIFY_RESUME)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
-#define _TIF_FSCHECK		(1 << TIF_FSCHECK)
 #define _TIF_SYSCALL_TRACE	(1 << TIF_SYSCALL_TRACE)
 #define _TIF_SYSCALL_AUDIT	(1 << TIF_SYSCALL_AUDIT)
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
···
 /*
  * Change these and you break ASM code in entry-common.S
  */
-#define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING |	\
-				 _TIF_NOTIFY_RESUME | _TIF_UPROBE |	\
-				 _TIF_FSCHECK)
+#define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
+				 _TIF_NOTIFY_RESUME | _TIF_UPROBE)
 
 #endif /* __KERNEL__ */
 #endif /* __ASM_ARM_THREAD_INFO_H */

arch/arm/include/asm/uaccess.h

···
 {
 	current_thread_info()->addr_limit = fs;
 	modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER);
-	/* On user-mode return, check fs is correct */
-	set_thread_flag(TIF_FSCHECK);
 }
 
 #define segment_eq(a, b)	((a) == (b))

arch/arm/kernel/entry-common.S

···
 #include <asm/unistd.h>
 #include <asm/ftrace.h>
 #include <asm/unwind.h>
+#include <asm/memory.h>
 #ifdef CONFIG_AEABI
 #include <asm/unistd-oabi.h>
 #endif
···
  UNWIND(.fnstart	)
  UNWIND(.cantunwind	)
 	disable_irq_notrace			@ disable interrupts
+	ldr	r2, [tsk, #TI_ADDR_LIMIT]
+	cmp	r2, #TASK_SIZE
+	blne	addr_limit_check_failed
 	ldr	r1, [tsk, #TI_FLAGS]		@ re-check for syscall tracing
-	tst	r1, #_TIF_SYSCALL_WORK
+	tst	r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
 	bne	fast_work_pending
-	tst	r1, #_TIF_WORK_MASK
-	bne	fast_work_pending
+
 
 	/* perform architecture specific actions before user return */
 	arch_ret_to_user r1, lr
···
  UNWIND(.cantunwind	)
 	str	r0, [sp, #S_R0 + S_OFF]!	@ save returned r0
 	disable_irq_notrace			@ disable interrupts
+	ldr	r2, [tsk, #TI_ADDR_LIMIT]
+	cmp	r2, #TASK_SIZE
+	blne	addr_limit_check_failed
 	ldr	r1, [tsk, #TI_FLAGS]		@ re-check for syscall tracing
-	tst	r1, #_TIF_SYSCALL_WORK
-	bne	fast_work_pending
-	tst	r1, #_TIF_WORK_MASK
+	tst	r1, #_TIF_SYSCALL_WORK | _TIF_WORK_MASK
 	beq	no_work_pending
  UNWIND(.fnend		)
 ENDPROC(ret_fast_syscall)
 
 	/* Slower path - fall through to work_pending */
-fast_work_pending:
 #endif
 
 	tst	r1, #_TIF_SYSCALL_WORK
···
 ret_slow_syscall:
 	disable_irq_notrace			@ disable interrupts
 ENTRY(ret_to_user_from_irq)
+	ldr	r2, [tsk, #TI_ADDR_LIMIT]
+	cmp	r2, #TASK_SIZE
+	blne	addr_limit_check_failed
 	ldr	r1, [tsk, #TI_FLAGS]
 	tst	r1, #_TIF_WORK_MASK
 	bne	slow_work_pending

arch/arm/kernel/signal.c

···
 	 * Update the trace code with the current status.
 	 */
 	trace_hardirqs_off();
-
-	/* Check valid user FS if needed */
-	addr_limit_user_check();
-
 	do {
 		if (likely(thread_flags & _TIF_NEED_RESCHED)) {
 			schedule();
···
 	flush_icache_range(ptr, ptr + sizeof(sigreturn_codes));
 
 	return page;
+}
+
+/* Defer to generic check */
+asmlinkage void addr_limit_check_failed(void)
+{
+	addr_limit_user_check();
 }

arch/arm64/kernel/signal.c

···
 	 */
 	trace_hardirqs_off();
 
-	/* Check valid user FS if needed */
-	addr_limit_user_check();
-
 	do {
+		/* Check valid user FS if needed */
+		addr_limit_user_check();
+
 		if (thread_flags & _TIF_NEED_RESCHED) {
 			schedule();
 		} else {

include/linux/syscalls.h

···
 	}								\
 	static inline long SYSC##name(__MAP(x,__SC_DECL,__VA_ARGS__))
 
-#ifdef TIF_FSCHECK
 /*
  * Called before coming back to user-mode. Returning to user-mode with an
  * address limit different than USER_DS can allow to overwrite kernel memory.
  */
 static inline void addr_limit_user_check(void)
 {
-
+#ifdef TIF_FSCHECK
 	if (!test_thread_flag(TIF_FSCHECK))
 		return;
-
-	BUG_ON(!segment_eq(get_fs(), USER_DS));
-	clear_thread_flag(TIF_FSCHECK);
-}
 #endif
+
+	if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS),
+				  "Invalid address limit on user-mode return"))
+		force_sig(SIGKILL, current);
+
+#ifdef TIF_FSCHECK
+	clear_thread_flag(TIF_FSCHECK);
+#endif
+}
 
 asmlinkage long sys32_quotactl(unsigned int cmd, const char __user *special,
 			       qid_t id, void __user *addr);