sh: Fixup __strnlen_user() behaviour.

Drop TIF_USERSPACE and add addr_limit to the thread_info struct.
Subsequently, use that for address checking in strnlen_user() to
ward off bogus -EFAULTs.

Make __strnlen_user() return 0 on exception, rather than -EFAULT.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/process.c

@@ -263,6 +263,7 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
 		unsigned long unused,
 		struct task_struct *p, struct pt_regs *regs)
 {
+	struct thread_info *ti = task_thread_info(p);
 	struct pt_regs *childregs;
 #if defined(CONFIG_SH_FPU)
 	struct task_struct *tsk = current;
@@ -277,8 +278,10 @@ int copy_thread(int nr, unsigned long clone_flags, unsigned long usp,
 
 	if (user_mode(regs)) {
 		childregs->regs[15] = usp;
+		ti->addr_limit = USER_DS;
 	} else {
 		childregs->regs[15] = (unsigned long)task_stack_page(p) + THREAD_SIZE;
+		ti->addr_limit = KERNEL_DS;
 	}
         if (clone_flags & CLONE_SETTLS) {
 		childregs->gbr = childregs->regs[0];

include/asm-sh/processor.h

@@ -149,6 +149,10 @@ struct thread_struct {
 	union sh_fpu_union fpu;
 };
 
+typedef struct {
+	unsigned long seg;
+} mm_segment_t;
+
 /* Count of active tasks with UBC settings */
 extern int ubc_usercnt;
 

include/asm-sh/thread_info.h

@@ -21,6 +21,7 @@ struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	__u32			cpu;
 	int			preempt_count; /* 0 => preemptable, <0 => BUG */
+	mm_segment_t		addr_limit;	/* thread address space */
 	struct restart_block	restart_block;
 	__u8			supervisor_stack[0];
 };
@@ -40,6 +41,7 @@ struct thread_info {
 	.flags		= 0,			\
 	.cpu		= 0,			\
 	.preempt_count	= 1,			\
+	.addr_limit	= KERNEL_DS,		\
 	.restart_block	= {			\
 		.fn = do_no_restart_syscall,	\
 	},					\
@@ -95,7 +97,6 @@ static inline struct thread_info *current_thread_info(void)
 #define TIF_USEDFPU		16	/* FPU was used by this task this quantum (SMP) */
 #define TIF_POLLING_NRFLAG	17	/* true if poll_idle() is polling TIF_NEED_RESCHED */
 #define TIF_MEMDIE		18
-#define TIF_USERSPACE		31	/* true if FS sets userspace */
 
 #define _TIF_SYSCALL_TRACE	(1<<TIF_SYSCALL_TRACE)
 #define _TIF_NOTIFY_RESUME	(1<<TIF_NOTIFY_RESUME)
@@ -103,7 +104,6 @@ static inline struct thread_info *current_thread_info(void)
 #define _TIF_NEED_RESCHED	(1<<TIF_NEED_RESCHED)
 #define _TIF_USEDFPU		(1<<TIF_USEDFPU)
 #define _TIF_POLLING_NRFLAG	(1<<TIF_POLLING_NRFLAG)
-#define _TIF_USERSPACE		(1<<TIF_USERSPACE)
 
 #define _TIF_WORK_MASK		0x000000FE	/* work to do on interrupt/exception return */
 #define _TIF_ALLWORK_MASK	0x000000FF	/* work to do on any return to u-space */

include/asm-sh/uaccess.h

@@ -16,21 +16,9 @@
 #include <linux/errno.h>
 #include <linux/sched.h>
 
-/*
- * NOTE: Macro/functions in this file depends on threads_info.h implementation.
- * Assumes:
- * TI_FLAGS == 8
- * TIF_USERSPACE == 31
- * USER_ADDR_LIMIT == 0x80000000
- */
-
 #define VERIFY_READ    0
 #define VERIFY_WRITE   1
 
-typedef struct {
-	unsigned int is_user_space;
-} mm_segment_t;
-
 /*
  * The fs value determines whether argument validity checking should be
  * performed or not.  If get_fs() == USER_DS, checking is performed, with
@@ -40,12 +28,14 @@ typedef struct {
  */
 
 #define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
-#define segment_eq(a,b)	((a).is_user_space == (b).is_user_space)
 
-#define USER_ADDR_LIMIT	0x80000000
+#define KERNEL_DS	MAKE_MM_SEG(0xFFFFFFFFUL)
+#define USER_DS		MAKE_MM_SEG(PAGE_OFFSET)
+
+#define segment_eq(a,b)	((a).seg == (b).seg)
 
-#define KERNEL_DS	MAKE_MM_SEG(0)
-#define USER_DS		MAKE_MM_SEG(1)
+#define __addr_ok(addr) \
+	((unsigned long)(addr) < (current_thread_info()->addr_limit.seg))
 
 #define get_ds()	(KERNEL_DS)
 
@@ -76,31 +66,8 @@ static inline int __access_ok(unsigned long addr, unsigned long size)
 	return ((addr >= memory_start) && ((addr + size) < memory_end));
 }
 #else /* CONFIG_MMU */
-static inline mm_segment_t get_fs(void)
-{
-	return MAKE_MM_SEG(test_thread_flag(TIF_USERSPACE));
-}
-
-static inline void set_fs(mm_segment_t s)
-{
-	unsigned long ti, flag;
-	__asm__ __volatile__(
-		"stc	r7_bank, %0\n\t"
-		"mov.l	@(8,%0), %1\n\t"
-		"shal	%1\n\t"
-		"cmp/pl	%2\n\t"
-		"rotcr	%1\n\t"
-		"mov.l	%1, @(8,%0)"
-		: "=&r" (ti), "=&r" (flag)
-		: "r" (s.is_user_space)
-		: "t");
-/****
-	if (s.is_user_space)
-		set_thread_flag(TIF_USERSPACE);
-	else
-		clear_thread_flag(TIF_USERSPACE);
-****/
-}
+#define get_fs()	(current_thread_info()->addr_limit)
+#define set_fs(x)	(current_thread_info()->addr_limit = (x))
 
 /*
  * __access_ok: Check if address with size is OK or not.
@@ -108,7 +75,7 @@ static inline void set_fs(mm_segment_t s)
  * We do three checks:
  * (1) is it user space? 
  * (2) addr + size --> carry?
- * (3) addr + size >= 0x80000000  (USER_ADDR_LIMIT)
+ * (3) addr + size >= 0x80000000  (PAGE_OFFSET)
  *
  * (1) (2) (3) | RESULT
  *  0   0   0  |  ok
@@ -541,7 +508,7 @@ static __inline__ long __strnlen_user(const char __user *__s, long __n)
 		"3:\n\t"
 		"mov.l	4f, %1\n\t"
 		"jmp	@%1\n\t"
-		" mov	%5, %0\n"
+		" mov	#0, %0\n"
 		".balign 4\n"
 		"4:	.long 2b\n"
 		".previous\n"
@@ -550,26 +517,20 @@ static __inline__ long __strnlen_user(const char __user *__s, long __n)
 		"	.long 1b,3b\n"
 		".previous"
 		: "=z" (res), "=&r" (__dummy)
-		: "0" (0), "r" (__s), "r" (__n), "i" (-EFAULT)
+		: "0" (0), "r" (__s), "r" (__n)
 		: "t");
 	return res;
 }
 
 static __inline__ long strnlen_user(const char __user *s, long n)
 {
-	if (!access_ok(VERIFY_READ, s, n))
+	if (!__addr_ok(s))
 		return 0;
 	else
 		return __strnlen_user(s, n);
 }
 
-static __inline__ long strlen_user(const char __user *s)
-{
-	if (!access_ok(VERIFY_READ, s, 0))
-		return 0;
-	else
-		return __strnlen_user(s, ~0UL >> 1);
-}
+#define strlen_user(str)	strnlen_user(str, ~0UL >> 1)
 
 /*
  * The exception table consists of pairs of addresses: the first is the