ARM: 9113/1: uaccess: remove set_fs() implementation

There are no remaining callers of set_fs(), so just remove it
along with all associated code that operates on
thread_info->addr_limit.

There are still further optimizations that can be done:

- In get_user(), the address check could be moved entirely
  into the out of line code, rather than passing a constant
  as an argument,

- I assume the DACR handling can be simplified as we now
  only change it during user access when CONFIG_CPU_SW_DOMAIN_PAN
  is set, but not during set_fs().

Acked-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>

4 files changed, 4 insertions, 53 deletions

diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
index 91d6b7856be4..93051e2f402c 100644
--- a/arch/arm/include/asm/ptrace.h
+++ b/arch/arm/include/asm/ptrace.h
@@ -19,7 +19,6 @@ struct pt_regs {
 struct svc_pt_regs {
 	struct pt_regs regs;
 	u32 dacr;
-	u32 addr_limit;
 };
 
 #define to_svc_pt_regs(r) container_of(r, struct svc_pt_regs, regs)
diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
index 17c56051747b..d89931aed59f 100644
--- a/arch/arm/include/asm/thread_info.h
+++ b/arch/arm/include/asm/thread_info.h
@@ -31,8 +31,6 @@ struct task_struct;
 
 #include <asm/types.h>
 
-typedef unsigned long mm_segment_t;
-
 struct cpu_context_save {
 	__u32	r4;
 	__u32	r5;
@@ -54,7 +52,6 @@ struct cpu_context_save {
 struct thread_info {
 	unsigned long		flags;		/* low level flags */
 	int			preempt_count;	/* 0 => preemptable, <0 => bug */
-	mm_segment_t		addr_limit;	/* address limit */
 	struct task_struct	*task;		/* main task structure */
 	__u32			cpu;		/* cpu */
 	__u32			cpu_domain;	/* cpu domain */
@@ -80,7 +77,6 @@ struct thread_info {
 	.task		= &tsk,						\
 	.flags		= 0,						\
 	.preempt_count	= INIT_PREEMPT_COUNT,				\
-	.addr_limit	= KERNEL_DS,					\
 }
 
 /*
diff --git a/arch/arm/include/asm/uaccess-asm.h b/arch/arm/include/asm/uaccess-asm.h
index e6eb7a2aaf1e..6451a433912c 100644
--- a/arch/arm/include/asm/uaccess-asm.h
+++ b/arch/arm/include/asm/uaccess-asm.h
@@ -84,12 +84,8 @@
 	 * if \disable is set.
 	 */
 	.macro	uaccess_entry, tsk, tmp0, tmp1, tmp2, disable
-	ldr	\tmp1, [\tsk, #TI_ADDR_LIMIT]
-	ldr	\tmp2, =TASK_SIZE
-	str	\tmp2, [\tsk, #TI_ADDR_LIMIT]
  DACR(	mrc	p15, 0, \tmp0, c3, c0, 0)
  DACR(	str	\tmp0, [sp, #SVC_DACR])
-	str	\tmp1, [sp, #SVC_ADDR_LIMIT]
 	.if \disable && IS_ENABLED(CONFIG_CPU_SW_DOMAIN_PAN)
 	/* kernel=client, user=no access */
 	mov	\tmp2, #DACR_UACCESS_DISABLE
@@ -106,9 +102,7 @@
 
 	/* Restore the user access state previously saved by uaccess_entry */
 	.macro	uaccess_exit, tsk, tmp0, tmp1
-	ldr	\tmp1, [sp, #SVC_ADDR_LIMIT]
  DACR(	ldr	\tmp0, [sp, #SVC_DACR])
-	str	\tmp1, [\tsk, #TI_ADDR_LIMIT]
  DACR(	mcr	p15, 0, \tmp0, c3, c0, 0)
 	.endm
 
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index 4f60638755c4..084d1c07c2d0 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -52,32 +52,8 @@ static __always_inline void uaccess_restore(unsigned int flags)
 extern int __get_user_bad(void);
 extern int __put_user_bad(void);
 
-/*
- * Note that this is actually 0x1,0000,0000
- */
-#define KERNEL_DS	0x00000000
-
 #ifdef CONFIG_MMU
 
-#define USER_DS		TASK_SIZE
-#define get_fs()	(current_thread_info()->addr_limit)
-
-static inline void set_fs(mm_segment_t fs)
-{
-	current_thread_info()->addr_limit = fs;
-
-	/*
-	 * Prevent a mispredicted conditional call to set_fs from forwarding
-	 * the wrong address limit to access_ok under speculation.
-	 */
-	dsb(nsh);
-	isb();
-
-	modify_domain(DOMAIN_KERNEL, fs ? DOMAIN_CLIENT : DOMAIN_MANAGER);
-}
-
-#define uaccess_kernel()	(get_fs() == KERNEL_DS)
-
 /*
  * We use 33-bit arithmetic here.  Success returns zero, failure returns
  * addr_limit.  We take advantage that addr_limit will be zero for KERNEL_DS,
@@ -89,7 +65,7 @@ static inline void set_fs(mm_segment_t fs)
 	__asm__(".syntax unified\n" \
 		"adds %1, %2, %3; sbcscc %1, %1, %0; movcc %0, #0" \
 		: "=&r" (flag), "=&r" (roksum) \
-		: "r" (addr), "Ir" (size), "0" (current_thread_info()->addr_limit) \
+		: "r" (addr), "Ir" (size), "0" (TASK_SIZE) \
 		: "cc"); \
 	flag; })
 
@@ -120,7 +96,7 @@ static inline void __user *__uaccess_mask_range_ptr(const void __user *ptr,
 	"	subshs	%1, %1, %2\n"
 	"	movlo	%0, #0\n"
 	: "+r" (safe_ptr), "=&r" (tmp)
-	: "r" (size), "r" (current_thread_info()->addr_limit)
+	: "r" (size), "r" (TASK_SIZE)
 	: "cc");
 
 	csdb();
@@ -194,7 +170,7 @@ extern int __get_user_64t_4(void *);
 
 #define __get_user_check(x, p)						\
 	({								\
-		unsigned long __limit = current_thread_info()->addr_limit - 1; \
+		unsigned long __limit = TASK_SIZE - 1; \
 		register typeof(*(p)) __user *__p asm("r0") = (p);	\
 		register __inttype(x) __r2 asm("r2");			\
 		register unsigned long __l asm("r1") = __limit;		\
@@ -245,7 +221,7 @@ extern int __put_user_8(void *, unsigned long long);
 
 #define __put_user_check(__pu_val, __ptr, __err, __s)			\
 	({								\
-		unsigned long __limit = current_thread_info()->addr_limit - 1; \
+		unsigned long __limit = TASK_SIZE - 1; \
 		register typeof(__pu_val) __r2 asm("r2") = __pu_val;	\
 		register const void __user *__p asm("r0") = __ptr;	\
 		register unsigned long __l asm("r1") = __limit;		\
@@ -262,19 +238,8 @@ extern int __put_user_8(void *, unsigned long long);
 
 #else /* CONFIG_MMU */
 
-/*
- * uClinux has only one addr space, so has simplified address limits.
- */
-#define USER_DS			KERNEL_DS
-
-#define uaccess_kernel()	(true)
 #define __addr_ok(addr)		((void)(addr), 1)
 #define __range_ok(addr, size)	((void)(addr), 0)
-#define get_fs()		(KERNEL_DS)
-
-static inline void set_fs(mm_segment_t fs)
-{
-}
 
 #define get_user(x, p)	__get_user(x, p)
 #define __put_user_check __put_user_nocheck
@@ -283,9 +248,6 @@ static inline void set_fs(mm_segment_t fs)
 
 #define access_ok(addr, size)	(__range_ok(addr, size) == 0)
 
-#define user_addr_max() \
-	(uaccess_kernel() ? ~0UL : get_fs())
-
 #ifdef CONFIG_CPU_SPECTRE
 /*
  * When mitigating Spectre variant 1, it is not worth fixing the non-