Subject: [PATCH v2 13/18] uaccess: generalize access_ok()

From: Arnd Bergmann <[email-masked]>
Date: Wed, 16 Feb 2022 14:13:27 +0100

From: Arnd Bergmann <[email-masked]>

There are many different ways that access_ok() is defined across
architectures, but in the end, they all just compare against the
user_addr_max() value or they accept anything.

Provide one definition that works for most architectures, checking
against TASK_SIZE_MAX for user processes or skipping the check inside
of uaccess_kernel() sections.

For architectures without CONFIG_SET_FS(), this should be the fastest
check, as it comes down to a single comparison of a pointer against a
compile-time constant, while the architecture specific versions tend to
do something more complex for historic reasons or get something wrong.

Type checking for __user annotations is handled inconsistently across
architectures, but this is easily simplified as well by using an inline
function that takes a 'const void __user *' argument. A handful of
callers need an extra __user annotation for this.

Some architectures had trick to use 33-bit or 65-bit arithmetic on the
addresses to calculate the overflow, however this simpler version uses
fewer registers, which means it can produce better object code in the
end despite needing a second (statically predicted) branch.

Reviewed-by: Christoph Hellwig <[email-masked]>
Acked-by: Mark Rutland <[email-masked]> [arm64, asm-generic]
Signed-off-by: Arnd Bergmann <[email-masked]>
---
 arch/Kconfig                          |  7 ++++
 arch/alpha/include/asm/uaccess.h      | 34 +++------------
 arch/arc/include/asm/uaccess.h        | 29 -------------
 arch/arm/include/asm/uaccess.h        | 20 +--------
 arch/arm64/include/asm/uaccess.h      | 11 ++---
 arch/csky/include/asm/uaccess.h       |  8 ----
 arch/hexagon/include/asm/uaccess.h    | 25 ------------
 arch/ia64/include/asm/uaccess.h       |  5 +--
 arch/m68k/Kconfig.cpu                 |  1 +
 arch/m68k/include/asm/uaccess.h       | 19 +--------
 arch/microblaze/include/asm/uaccess.h |  8 +---
 arch/mips/include/asm/uaccess.h       | 29 +------------
 arch/nds32/include/asm/uaccess.h      |  7 +---
 arch/nios2/include/asm/uaccess.h      | 11 +----
 arch/openrisc/include/asm/uaccess.h   | 19 +--------
 arch/parisc/Kconfig                   |  1 +
 arch/parisc/include/asm/uaccess.h     | 12 ++----
 arch/powerpc/include/asm/uaccess.h    | 11 +----
 arch/riscv/include/asm/uaccess.h      | 31 +-------------
 arch/s390/Kconfig                     |  1 +
 arch/s390/include/asm/uaccess.h       | 14 +------
 arch/sh/include/asm/uaccess.h         | 22 +---------
 arch/sparc/Kconfig                    |  1 +
 arch/sparc/include/asm/uaccess.h      |  3 --
 arch/sparc/include/asm/uaccess_32.h   | 18 ++------
 arch/sparc/include/asm/uaccess_64.h   | 12 +-----
 arch/um/include/asm/uaccess.h         |  5 ++-
 arch/x86/include/asm/uaccess.h        | 14 +------
 arch/xtensa/include/asm/uaccess.h     | 10 +----
 include/asm-generic/access_ok.h       | 59 +++++++++++++++++++++++++++
 include/asm-generic/uaccess.h         | 21 +---------
 include/linux/uaccess.h               |  7 ----
 32 files changed, 109 insertions(+), 366 deletions(-)
 create mode 100644 include/asm-generic/access_ok.h

diff --git a/arch/Kconfig b/arch/Kconfig
index 678a80713b21..fa5db36bda67 100644
--- a/arch/Kconfig
+++ b/arch/Kconfig
@@ -898,6 +898,13 @@ config HAVE_SOFTIRQ_ON_OWN_STACK
 	  Architecture provides a function to run __do_softirq() on a
 	  separate stack.
 
+config ALTERNATE_USER_ADDRESS_SPACE
+	bool
+	help
+	  Architectures set this when the CPU uses separate address
+	  spaces for kernel and user space pointers. In this case, the
+	  access_ok() check on a __user pointer is skipped.
+
 config PGTABLE_LEVELS
 	int
 	default 2
diff --git a/arch/alpha/include/asm/uaccess.h b/arch/alpha/include/asm/uaccess.h
index 1b6f25efa247..82c5743fc9cd 100644
--- a/arch/alpha/include/asm/uaccess.h
+++ b/arch/alpha/include/asm/uaccess.h
@@ -20,28 +20,7 @@
 #define get_fs()  (current_thread_info()->addr_limit)
 #define set_fs(x) (current_thread_info()->addr_limit = (x))
 
-#define uaccess_kernel()	(get_fs().seg == KERNEL_DS.seg)
-
-/*
- * Is a address valid? This does a straightforward calculation rather
- * than tests.
- *
- * Address valid if:
- *  - "addr" doesn't have any high-bits set
- *  - AND "size" doesn't have any high-bits set
- *  - AND "addr+size-(size != 0)" doesn't have any high-bits set
- *  - OR we are in kernel mode.
- */
-#define __access_ok(addr, size) ({				\
-	unsigned long __ao_a = (addr), __ao_b = (size);		\
-	unsigned long __ao_end = __ao_a + __ao_b - !!__ao_b;	\
-	(get_fs().seg & (__ao_a | __ao_b | __ao_end)) == 0; })
-
-#define access_ok(addr, size)				\
-({							\
-	__chk_user_ptr(addr);				\
-	__access_ok(((unsigned long)(addr)), (size));	\
-})
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They automatically
@@ -105,7 +84,7 @@ extern void __get_user_unknown(void);
 	long __gu_err = -EFAULT;				\
 	unsigned long __gu_val = 0;				\
 	const __typeof__(*(ptr)) __user *__gu_addr = (ptr);	\
-	if (__access_ok((unsigned long)__gu_addr, size)) {	\
+	if (__access_ok(__gu_addr, size)) {			\
 		__gu_err = 0;					\
 		switch (size) {					\
 		  case 1: __get_user_8(__gu_addr); break;	\
@@ -200,7 +179,7 @@ extern void __put_user_unknown(void);
 ({								\
 	long __pu_err = -EFAULT;				\
 	__typeof__(*(ptr)) __user *__pu_addr = (ptr);		\
-	if (__access_ok((unsigned long)__pu_addr, size)) {	\
+	if (__access_ok(__pu_addr, size)) {			\
 		__pu_err = 0;					\
 		switch (size) {					\
 		  case 1: __put_user_8(x, __pu_addr); break;	\
@@ -316,17 +295,14 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long len)
 
 extern long __clear_user(void __user *to, long len);
 
-extern inline long
+static inline long
 clear_user(void __user *to, long len)
 {
-	if (__access_ok((unsigned long)to, len))
+	if (__access_ok(to, len))
 		len = __clear_user(to, len);
 	return len;
 }
 
-#define user_addr_max() \
-        (uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 extern long strncpy_from_user(char *dest, const char __user *src, long count);
 extern __must_check long strnlen_user(const char __user *str, long n);
 
diff --git a/arch/arc/include/asm/uaccess.h b/arch/arc/include/asm/uaccess.h
index 783bfdb3bfa3..30f80b4be2ab 100644
--- a/arch/arc/include/asm/uaccess.h
+++ b/arch/arc/include/asm/uaccess.h
@@ -23,35 +23,6 @@
 
 #include <linux/string.h>	/* for generic string functions */
 
-
-#define __kernel_ok		(uaccess_kernel())
-
-/*
- * Algorithmically, for __user_ok() we want do:
- * 	(start < TASK_SIZE) && (start+len < TASK_SIZE)
- * where TASK_SIZE could either be retrieved from thread_info->addr_limit or
- * emitted directly in code.
- *
- * This can however be rewritten as follows:
- *	(len <= TASK_SIZE) && (start+len < TASK_SIZE)
- *
- * Because it essentially checks if buffer end is within limit and @len is
- * non-ngeative, which implies that buffer start will be within limit too.
- *
- * The reason for rewriting being, for majority of cases, @len is generally
- * compile time constant, causing first sub-expression to be compile time
- * subsumed.
- *
- * The second part would generate weird large LIMMs e.g. (0x6000_0000 - 0x10),
- * so we check for TASK_SIZE using get_fs() since the addr_limit load from mem
- * would already have been done at this call site for __kernel_ok()
- *
- */
-#define __user_ok(addr, sz)	(((sz) <= TASK_SIZE) && \
-				 ((addr) <= (get_fs() - (sz))))
-#define __access_ok(addr, sz)	(unlikely(__kernel_ok) || \
-				 likely(__user_ok((addr), (sz))))
-
 /*********** Single byte/hword/word copies ******************/
 
 #define __get_user_fn(sz, u, k)					\
diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
index d20d78c34b94..2fcbec9c306c 100644
--- a/arch/arm/include/asm/uaccess.h
+++ b/arch/arm/include/asm/uaccess.h
@@ -55,21 +55,6 @@ extern int __put_user_bad(void);
 
 #ifdef CONFIG_MMU
 
-/*
- * 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,
- * so this will always return success in that case.
- */
-#define __range_ok(addr, size) ({ \
-	unsigned long flag, roksum; \
-	__chk_user_ptr(addr);	\
-	__asm__(".syntax unified\n" \
-		"adds %1, %2, %3; sbcscc %1, %1, %0; movcc %0, #0" \
-		: "=&r" (flag), "=&r" (roksum) \
-		: "r" (addr), "Ir" (size), "0" (TASK_SIZE) \
-		: "cc"); \
-	flag; })
-
 /*
  * This is a type: either unsigned long, if the argument fits into
  * that type, or otherwise unsigned long long.
@@ -241,15 +226,12 @@ extern int __put_user_8(void *, unsigned long long);
 
 #else /* CONFIG_MMU */
 
-#define __addr_ok(addr)		((void)(addr), 1)
-#define __range_ok(addr, size)	((void)(addr), 0)
-
 #define get_user(x, p)	__get_user(x, p)
 #define __put_user_check __put_user_nocheck
 
 #endif /* CONFIG_MMU */
 
-#define access_ok(addr, size)	(__range_ok(addr, size) == 0)
+#include <asm-generic/access_ok.h>
 
 #ifdef CONFIG_CPU_SPECTRE
 /*
diff --git a/arch/arm64/include/asm/uaccess.h b/arch/arm64/include/asm/uaccess.h
index 199c553b740a..e8dce0cc5eaa 100644
--- a/arch/arm64/include/asm/uaccess.h
+++ b/arch/arm64/include/asm/uaccess.h
@@ -26,13 +26,7 @@
 #include <asm/memory.h>
 #include <asm/extable.h>
 
-static inline int __access_ok(const void __user *ptr, unsigned long size)
-{
-	unsigned long limit = TASK_SIZE_MAX;
-	unsigned long addr = (unsigned long)ptr;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
+static inline int __access_ok(const void __user *ptr, unsigned long size);
 
 /*
  * Test whether a block of memory is a valid user space address.
@@ -54,6 +48,9 @@ static inline int access_ok(const void __user *addr, unsigned long size)
 
 	return likely(__access_ok(addr, size));
 }
+#define access_ok access_ok
+
+#include <asm-generic/access_ok.h>
 
 /*
  * User access enabling/disabling.
diff --git a/arch/csky/include/asm/uaccess.h b/arch/csky/include/asm/uaccess.h
index ac5a54f57d40..fec8f77ffc99 100644
--- a/arch/csky/include/asm/uaccess.h
+++ b/arch/csky/include/asm/uaccess.h
@@ -5,14 +5,6 @@
 
 #define user_addr_max() (current_thread_info()->addr_limit.seg)
 
-static inline int __access_ok(unsigned long addr, unsigned long size)
-{
-	unsigned long limit = user_addr_max();
-
-	return (size <= limit) && (addr <= (limit - size));
-}
-#define __access_ok __access_ok
-
 /*
  * __put_user_fn
  */
diff --git a/arch/hexagon/include/asm/uaccess.h b/arch/hexagon/include/asm/uaccess.h
index 719ba3f3c45c..bff77efc0d9a 100644
--- a/arch/hexagon/include/asm/uaccess.h
+++ b/arch/hexagon/include/asm/uaccess.h
@@ -12,31 +12,6 @@
  */
 #include <asm/sections.h>
 
-/*
- * access_ok: - Checks if a user space pointer is valid
- * @addr: User space pointer to start of block to check
- * @size: Size of block to check
- *
- * Context: User context only. This function may sleep if pagefaults are
- *          enabled.
- *
- * Checks if a pointer to a block of memory in user space is valid.
- *
- * Returns true (nonzero) if the memory block *may* be valid, false (zero)
- * if it is definitely invalid.
- *
- */
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
-
-static inline int __access_ok(unsigned long addr, unsigned long size)
-{
-	unsigned long limit = TASK_SIZE;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
-#define __access_ok __access_ok
-
 /*
  * When a kernel-mode page fault is taken, the faulting instruction
  * address is checked against a table of exception_table_entries.
diff --git a/arch/ia64/include/asm/uaccess.h b/arch/ia64/include/asm/uaccess.h
index e19d2dcc0ced..e242a3cc1330 100644
--- a/arch/ia64/include/asm/uaccess.h
+++ b/arch/ia64/include/asm/uaccess.h
@@ -50,8 +50,6 @@
 #define get_fs()  (current_thread_info()->addr_limit)
 #define set_fs(x) (current_thread_info()->addr_limit = (x))
 
-#define uaccess_kernel()	(get_fs().seg == KERNEL_DS.seg)
-
 /*
  * When accessing user memory, we need to make sure the entire area really is in
  * user-level space.  In order to do this efficiently, we make sure that the page at
@@ -65,7 +63,8 @@ static inline int __access_ok(const void __user *p, unsigned long size)
 	return likely(addr <= seg) &&
 	 (seg == KERNEL_DS.seg || likely(REGION_OFFSET(addr) < RGN_MAP_LIMIT));
 }
-#define access_ok(addr, size)	__access_ok((addr), (size))
+#define __access_ok __access_ok
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They automatically
diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
index 0d00ef5117dc..16ea9a67723c 100644
--- a/arch/m68k/Kconfig.cpu
+++ b/arch/m68k/Kconfig.cpu
@@ -453,6 +453,7 @@ config CPU_HAS_NO_UNALIGNED
 
 config CPU_HAS_ADDRESS_SPACES
 	bool
+	select ALTERNATE_USER_ADDRESS_SPACE
 
 config FPU
 	bool
diff --git a/arch/m68k/include/asm/uaccess.h b/arch/m68k/include/asm/uaccess.h
index 8eb625e75452..64914872a5c9 100644
--- a/arch/m68k/include/asm/uaccess.h
+++ b/arch/m68k/include/asm/uaccess.h
@@ -10,24 +10,7 @@
 #include <linux/compiler.h>
 #include <linux/types.h>
 #include <asm/extable.h>
-
-/* We let the MMU do all checking */
-static inline int access_ok(const void __user *ptr,
-			    unsigned long size)
-{
-	unsigned long limit = TASK_SIZE;
-	unsigned long addr = (unsigned long)ptr;
-
-	/*
-	 * XXX: for !CONFIG_CPU_HAS_ADDRESS_SPACES this really needs to check
-	 * for TASK_SIZE!
-	 * Removing this helper is probably sufficient.
-	 */
-	if (IS_ENABLED(CONFIG_CPU_HAS_ADDRESS_SPACES))
-		return 1;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
+#include <asm-generic/access_ok.h>
 
 /*
  * Not all varients of the 68k family support the notion of address spaces.
diff --git a/arch/microblaze/include/asm/uaccess.h b/arch/microblaze/include/asm/uaccess.h
index 3fe96979d2c6..bf9b7657a65a 100644
--- a/arch/microblaze/include/asm/uaccess.h
+++ b/arch/microblaze/include/asm/uaccess.h
@@ -39,13 +39,7 @@
 
 # define uaccess_kernel()	(get_fs().seg == KERNEL_DS.seg)
 
-static inline int __access_ok(unsigned long addr, unsigned long size)
-{
-	unsigned long limit = user_addr_max();
-
-	return (size <= limit) && (addr <= (limit - size));
-}
-#define access_ok(addr, size) __access_ok((unsigned long)addr, size)
+#include <asm-generic/access_ok.h>
 
 # define __FIXUP_SECTION	".section .fixup,\"ax\"\n"
 # define __EX_TABLE_SECTION	".section __ex_table,\"a\"\n"
diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h
index d7c89dc3426c..436248652b28 100644
--- a/arch/mips/include/asm/uaccess.h
+++ b/arch/mips/include/asm/uaccess.h
@@ -44,34 +44,7 @@ extern u64 __ua_limit;
 
 #endif /* CONFIG_64BIT */
 
-/*
- * access_ok: - Checks if a user space pointer is valid
- * @addr: User space pointer to start of block to check
- * @size: Size of block to check
- *
- * Context: User context only. This function may sleep if pagefaults are
- *          enabled.
- *
- * Checks if a pointer to a block of memory in user space is valid.
- *
- * Returns true (nonzero) if the memory block may be valid, false (zero)
- * if it is definitely invalid.
- *
- * Note that, depending on architecture, this function probably just
- * checks that the pointer is in the user space range - after calling
- * this function, memory access functions may still return -EFAULT.
- */
-
-static inline int __access_ok(const void __user *p, unsigned long size)
-{
-	unsigned long addr = (unsigned long)p;
-	unsigned long limit = TASK_SIZE_MAX;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
-
-#define access_ok(addr, size)					\
-	likely(__access_ok((addr), (size)))
+#include <asm-generic/access_ok.h>
 
 /*
  * put_user: - Write a simple value into user space.
diff --git a/arch/nds32/include/asm/uaccess.h b/arch/nds32/include/asm/uaccess.h
index 37a40981deb3..832d642a4068 100644
--- a/arch/nds32/include/asm/uaccess.h
+++ b/arch/nds32/include/asm/uaccess.h
@@ -38,18 +38,15 @@ extern int fixup_exception(struct pt_regs *regs);
 
 #define get_fs()	(current_thread_info()->addr_limit)
 #define user_addr_max	get_fs
+#define uaccess_kernel() (get_fs() == KERNEL_DS)
 
 static inline void set_fs(mm_segment_t fs)
 {
 	current_thread_info()->addr_limit = fs;
 }
 
-#define uaccess_kernel()	(get_fs() == KERNEL_DS)
+#include <asm-generic/access_ok.h>
 
-#define __range_ok(addr, size) (size <= get_fs() && addr <= (get_fs() -size))
-
-#define access_ok(addr, size)	\
-	__range_ok((unsigned long)addr, (unsigned long)size)
 /*
  * Single-value transfer routines.  They automatically use the right
  * size if we just have the right pointer type.  Note that the functions
diff --git a/arch/nios2/include/asm/uaccess.h b/arch/nios2/include/asm/uaccess.h
index a5cbe07cf0da..6664ddc0e8e5 100644
--- a/arch/nios2/include/asm/uaccess.h
+++ b/arch/nios2/include/asm/uaccess.h
@@ -30,19 +30,10 @@
 #define get_fs()		(current_thread_info()->addr_limit)
 #define set_fs(seg)		(current_thread_info()->addr_limit = (seg))
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-
-#define __access_ok(addr, len)			\
-	(((signed long)(((long)get_fs().seg) &	\
-		((long)(addr) | (((long)(addr)) + (len)) | (len)))) == 0)
-
-#define access_ok(addr, len)		\
-	likely(__access_ok((unsigned long)(addr), (unsigned long)(len)))
+#include <asm-generic/access_ok.h>
 
 # define __EX_TABLE_SECTION	".section __ex_table,\"a\"\n"
 
-#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 /*
  * Zero Userspace
  */
diff --git a/arch/openrisc/include/asm/uaccess.h b/arch/openrisc/include/asm/uaccess.h
index 120f5005461b..8f049ec99b3e 100644
--- a/arch/openrisc/include/asm/uaccess.h
+++ b/arch/openrisc/include/asm/uaccess.h
@@ -45,21 +45,7 @@
 
 #define uaccess_kernel()	(get_fs() == KERNEL_DS)
 
-/* Ensure that the range from addr to addr+size is all within the process'
- * address space
- */
-static inline int __range_ok(unsigned long addr, unsigned long size)
-{
-	const mm_segment_t fs = get_fs();
-
-	return size <= fs && addr <= (fs - size);
-}
-
-#define access_ok(addr, size)						\
-({ 									\
-	__chk_user_ptr(addr);						\
-	__range_ok((unsigned long)(addr), (size));			\
-})
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They automatically
@@ -268,9 +254,6 @@ clear_user(void __user *addr, unsigned long size)
 	return size;
 }
 
-#define user_addr_max() \
-	(uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 extern long strncpy_from_user(char *dest, const char __user *src, long count);
 
 extern __must_check long strnlen_user(const char __user *str, long n);
diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 43c1c880def6..15039fdd5413 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 config PARISC
 	def_bool y
+	select ALTERNATE_USER_ADDRESS_SPACE
 	select ARCH_32BIT_OFF_T if !64BIT
 	select ARCH_MIGHT_HAVE_PC_PARPORT
 	select HAVE_FUNCTION_TRACER
diff --git a/arch/parisc/include/asm/uaccess.h b/arch/parisc/include/asm/uaccess.h
index 0925bbd6db67..187f4bdff13e 100644
--- a/arch/parisc/include/asm/uaccess.h
+++ b/arch/parisc/include/asm/uaccess.h
@@ -11,15 +11,9 @@
 #include <linux/bug.h>
 #include <linux/string.h>
 
-/*
- * Note that since kernel addresses are in a separate address space on
- * parisc, we don't need to do anything for access_ok().
- * We just let the page fault handler do the right thing. This also means
- * that put_user is the same as __put_user, etc.
- */
-
-#define access_ok(uaddr, size)	\
-	( (uaddr) == (uaddr) )
+#define TASK_SIZE_MAX DEFAULT_TASK_SIZE
+#include <asm/pgtable.h>
+#include <asm-generic/access_ok.h>
 
 #define put_user __put_user
 #define get_user __get_user
diff --git a/arch/powerpc/include/asm/uaccess.h b/arch/powerpc/include/asm/uaccess.h
index a0032c2e7550..2e83217f52de 100644
--- a/arch/powerpc/include/asm/uaccess.h
+++ b/arch/powerpc/include/asm/uaccess.h
@@ -11,18 +11,9 @@
 #ifdef __powerpc64__
 /* We use TASK_SIZE_USER64 as TASK_SIZE is not constant */
 #define TASK_SIZE_MAX		TASK_SIZE_USER64
-#else
-#define TASK_SIZE_MAX		TASK_SIZE
 #endif
 
-static inline bool __access_ok(unsigned long addr, unsigned long size)
-{
-	return addr < TASK_SIZE_MAX && size <= TASK_SIZE_MAX - addr;
-}
-
-#define access_ok(addr, size)		\
-	(__chk_user_ptr(addr),		\
-	 __access_ok((unsigned long)(addr), (size)))
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They automatically
diff --git a/arch/riscv/include/asm/uaccess.h b/arch/riscv/include/asm/uaccess.h
index 4407b9e48d2c..855450bed9f5 100644
--- a/arch/riscv/include/asm/uaccess.h
+++ b/arch/riscv/include/asm/uaccess.h
@@ -21,42 +21,13 @@
 #include <asm/byteorder.h>
 #include <asm/extable.h>
 #include <asm/asm.h>
+#include <asm-generic/access_ok.h>
 
 #define __enable_user_access()							\
 	__asm__ __volatile__ ("csrs sstatus, %0" : : "r" (SR_SUM) : "memory")
 #define __disable_user_access()							\
 	__asm__ __volatile__ ("csrc sstatus, %0" : : "r" (SR_SUM) : "memory")
 
-/**
- * access_ok: - Checks if a user space pointer is valid
- * @addr: User space pointer to start of block to check
- * @size: Size of block to check
- *
- * Context: User context only.  This function may sleep.
- *
- * Checks if a pointer to a block of memory in user space is valid.
- *
- * Returns true (nonzero) if the memory block may be valid, false (zero)
- * if it is definitely invalid.
- *
- * Note that, depending on architecture, this function probably just
- * checks that the pointer is in the user space range - after calling
- * this function, memory access functions may still return -EFAULT.
- */
-#define access_ok(addr, size) ({					\
-	__chk_user_ptr(addr);						\
-	likely(__access_ok((unsigned long __force)(addr), (size)));	\
-})
-
-/*
- * Ensure that the range [addr, addr+size) is within the process's
- * address space
- */
-static inline int __access_ok(unsigned long addr, unsigned long size)
-{
-	return size <= TASK_SIZE && addr <= TASK_SIZE - size;
-}
-
 /*
  * The exception table consists of pairs of addresses: the first is the
  * address of an instruction that is allowed to fault, and the second is
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index be9f39fd06df..fb48a62aa985 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -55,6 +55,7 @@ config S390
 	# Note: keep this list sorted alphabetically
 	#
 	imply IMA_SECURE_AND_OR_TRUSTED_BOOT
+	select ALTERNATE_USER_ADDRESS_SPACE
 	select ARCH_32BIT_USTAT_F_TINODE
 	select ARCH_BINFMT_ELF_STATE
 	select ARCH_ENABLE_MEMORY_HOTPLUG if SPARSEMEM
diff --git a/arch/s390/include/asm/uaccess.h b/arch/s390/include/asm/uaccess.h
index 29332edf46f0..5cb258cd9d29 100644
--- a/arch/s390/include/asm/uaccess.h
+++ b/arch/s390/include/asm/uaccess.h
@@ -17,22 +17,10 @@
 #include <asm/ctl_reg.h>
 #include <asm/extable.h>
 #include <asm/facility.h>
+#include <asm-generic/access_ok.h>
 
 void debug_user_asce(int exit);
 
-static inline int __range_ok(unsigned long addr, unsigned long size)
-{
-	return 1;
-}
-
-#define __access_ok(addr, size)				\
-({							\
-	__chk_user_ptr(addr);				\
-	__range_ok((unsigned long)(addr), (size));	\
-})
-
-#define access_ok(addr, size) __access_ok(addr, size)
-
 unsigned long __must_check
 raw_copy_from_user(void *to, const void __user *from, unsigned long n);
 
diff --git a/arch/sh/include/asm/uaccess.h b/arch/sh/include/asm/uaccess.h
index 8867bb04b00e..ccd219d74851 100644
--- a/arch/sh/include/asm/uaccess.h
+++ b/arch/sh/include/asm/uaccess.h
@@ -5,28 +5,10 @@
 #include <asm/segment.h>
 #include <asm/extable.h>
 
-#define __addr_ok(addr) \
-	((unsigned long __force)(addr) < current_thread_info()->addr_limit.seg)
-
-/*
- * __access_ok: Check if address with size is OK or not.
- *
- * Uhhuh, this needs 33-bit arithmetic. We have a carry..
- *
- * sum := addr + size;  carry? --> flag = true;
- * if (sum >= addr_limit) flag = true;
- */
-#define __access_ok(addr, size)	({				\
-	unsigned long __ao_a = (addr), __ao_b = (size);		\
-	unsigned long __ao_end = __ao_a + __ao_b - !!__ao_b;	\
-	__ao_end >= __ao_a && __addr_ok(__ao_end); })
-
-#define access_ok(addr, size)	\
-	(__chk_user_ptr(addr),		\
-	 __access_ok((unsigned long __force)(addr), (size)))
-
 #define user_addr_max()	(current_thread_info()->addr_limit.seg)
 
+#include <asm-generic/access_ok.h>
+
 /*
  * Uh, these should become the main single-value transfer routines ...
  * They automatically use the right size if we just have the right
diff --git a/arch/sparc/Kconfig b/arch/sparc/Kconfig
index 1cab1b284f1a..9f6f9bce5292 100644
--- a/arch/sparc/Kconfig
+++ b/arch/sparc/Kconfig
@@ -62,6 +62,7 @@ config SPARC32
 
 config SPARC64
 	def_bool 64BIT
+	select ALTERNATE_USER_ADDRESS_SPACE
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_KRETPROBES
diff --git a/arch/sparc/include/asm/uaccess.h b/arch/sparc/include/asm/uaccess.h
index 390094200fc4..ee75f69e3fcd 100644
--- a/arch/sparc/include/asm/uaccess.h
+++ b/arch/sparc/include/asm/uaccess.h
@@ -10,9 +10,6 @@
 #include <asm/uaccess_32.h>
 #endif
 
-#define user_addr_max() \
-	(uaccess_kernel() ? ~0UL : TASK_SIZE)
-
 long strncpy_from_user(char *dest, const char __user *src, long count);
 
 #endif
diff --git a/arch/sparc/include/asm/uaccess_32.h b/arch/sparc/include/asm/uaccess_32.h
index 4a12346bb69c..367747116260 100644
--- a/arch/sparc/include/asm/uaccess_32.h
+++ b/arch/sparc/include/asm/uaccess_32.h
@@ -25,17 +25,7 @@
 #define get_fs()	(current->thread.current_ds)
 #define set_fs(val)	((current->thread.current_ds) = (val))
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-
-/* We have there a nice not-mapped page at PAGE_OFFSET - PAGE_SIZE, so that this test
- * can be fairly lightweight.
- * No one can read/write anything from userland in the kernel space by setting
- * large size and address near to PAGE_OFFSET - a fault will break his intentions.
- */
-#define __user_ok(addr, size) ({ (void)(size); (addr) < STACK_TOP; })
-#define __kernel_ok (uaccess_kernel())
-#define __access_ok(addr, size) (__user_ok((addr) & get_fs().seg, (size)))
-#define access_ok(addr, size) __access_ok((unsigned long)(addr), size)
+#include <asm-generic/access_ok.h>
 
 /* Uh, these should become the main single-value transfer routines..
  * They automatically use the right size if we just have the right
@@ -47,13 +37,13 @@
  * and hide all the ugliness from the user.
  */
 #define put_user(x, ptr) ({ \
-	unsigned long __pu_addr = (unsigned long)(ptr); \
+	void __user *__pu_addr = (ptr); \
 	__chk_user_ptr(ptr); \
 	__put_user_check((__typeof__(*(ptr)))(x), __pu_addr, sizeof(*(ptr))); \
 })
 
 #define get_user(x, ptr) ({ \
-	unsigned long __gu_addr = (unsigned long)(ptr); \
+	const void __user *__gu_addr = (ptr); \
 	__chk_user_ptr(ptr); \
 	__get_user_check((x), __gu_addr, sizeof(*(ptr)), __typeof__(*(ptr))); \
 })
@@ -232,7 +222,7 @@ static inline unsigned long __clear_user(void __user *addr, unsigned long size)
 
 static inline unsigned long clear_user(void __user *addr, unsigned long n)
 {
-	if (n && __access_ok((unsigned long) addr, n))
+	if (n && __access_ok(addr, n))
 		return __clear_user(addr, n);
 	else
 		return n;
diff --git a/arch/sparc/include/asm/uaccess_64.h b/arch/sparc/include/asm/uaccess_64.h
index 5c12fb46bc61..59b9a545df23 100644
--- a/arch/sparc/include/asm/uaccess_64.h
+++ b/arch/sparc/include/asm/uaccess_64.h
@@ -31,7 +31,7 @@
 
 #define get_fs() ((mm_segment_t){(current_thread_info()->current_ds)})
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
+#include <asm-generic/access_ok.h>
 
 #define set_fs(val)								\
 do {										\
@@ -61,16 +61,6 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
 	__chk_range_not_ok((unsigned long __force)(addr), size, limit); \
 })
 
-static inline int __access_ok(const void __user * addr, unsigned long size)
-{
-	return 1;
-}
-
-static inline int access_ok(const void __user * addr, unsigned long size)
-{
-	return 1;
-}
-
 void __retl_efault(void);
 
 /* Uh, these should become the main single-value transfer routines..
diff --git a/arch/um/include/asm/uaccess.h b/arch/um/include/asm/uaccess.h
index 1ecfc96bcc50..7d9d60e41e4e 100644
--- a/arch/um/include/asm/uaccess.h
+++ b/arch/um/include/asm/uaccess.h
@@ -25,7 +25,7 @@
 extern unsigned long raw_copy_from_user(void *to, const void __user *from, unsigned long n);
 extern unsigned long raw_copy_to_user(void __user *to, const void *from, unsigned long n);
 extern unsigned long __clear_user(void __user *mem, unsigned long len);
-static inline int __access_ok(unsigned long addr, unsigned long size);
+static inline int __access_ok(const void __user *ptr, unsigned long size);
 
 /* Teach asm-generic/uaccess.h that we have C functions for these. */
 #define __access_ok __access_ok
@@ -36,8 +36,9 @@ static inline int __access_ok(unsigned long addr, unsigned long size);
 
 #include <asm-generic/uaccess.h>
 
-static inline int __access_ok(unsigned long addr, unsigned long size)
+static inline int __access_ok(const void __user *ptr, unsigned long size)
 {
+	unsigned long addr = (unsigned long)ptr;
 	return __addr_range_nowrap(addr, size) &&
 		(__under_task_size(addr, size) ||
 		 __access_ok_vsyscall(addr, size));
diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index 201efcec66b7..f78e2b3501a1 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -12,18 +12,6 @@
 #include <asm/smap.h>
 #include <asm/extable.h>
 
-/*
- * Test whether a block of memory is a valid user space address.
- * Returns 0 if the range is valid, nonzero otherwise.
- */
-static inline bool __access_ok(void __user *ptr, unsigned long size)
-{
-	unsigned long limit = TASK_SIZE_MAX;
-	unsigned long addr = ptr;
-
-	return (size <= limit) && (addr <= (limit - size));
-}
-
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 static inline bool pagefault_disabled(void);
 # define WARN_ON_IN_IRQ()	\
@@ -55,6 +43,8 @@ static inline bool pagefault_disabled(void);
 	likely(__access_ok(addr, size));				\
 })
 
+#include <asm-generic/access_ok.h>
+
 extern int __get_user_1(void);
 extern int __get_user_2(void);
 extern int __get_user_4(void);
diff --git a/arch/xtensa/include/asm/uaccess.h b/arch/xtensa/include/asm/uaccess.h
index 75bd8fbf52ba..0edd9e4b23d0 100644
--- a/arch/xtensa/include/asm/uaccess.h
+++ b/arch/xtensa/include/asm/uaccess.h
@@ -35,15 +35,7 @@
 #define get_fs()	(current->thread.current_ds)
 #define set_fs(val)	(current->thread.current_ds = (val))
 
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-
-#define __kernel_ok (uaccess_kernel())
-#define __user_ok(addr, size) \
-		(((size) <= TASK_SIZE)&&((addr) <= TASK_SIZE-(size)))
-#define __access_ok(addr, size) (__kernel_ok || __user_ok((addr), (size)))
-#define access_ok(addr, size) __access_ok((unsigned long)(addr), (size))
-
-#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They
diff --git a/include/asm-generic/access_ok.h b/include/asm-generic/access_ok.h
new file mode 100644
index 000000000000..1aad8964d2ed
--- /dev/null
+++ b/include/asm-generic/access_ok.h
@@ -0,0 +1,59 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __ASM_GENERIC_ACCESS_OK_H__
+#define __ASM_GENERIC_ACCESS_OK_H__
+
+/*
+ * Checking whether a pointer is valid for user space access.
+ * These definitions work on most architectures, but overrides can
+ * be used where necessary.
+ */
+
+/*
+ * architectures with compat tasks have a variable TASK_SIZE and should
+ * override this to a constant.
+ */
+#ifndef TASK_SIZE_MAX
+#define TASK_SIZE_MAX			TASK_SIZE
+#endif
+
+#ifndef uaccess_kernel
+#ifdef CONFIG_SET_FS
+#define uaccess_kernel()		(get_fs().seg == KERNEL_DS.seg)
+#else
+#define uaccess_kernel()		(0)
+#endif
+#endif
+
+#ifndef user_addr_max
+#define user_addr_max()			(uaccess_kernel() ? ~0UL : TASK_SIZE_MAX)
+#endif
+
+#ifndef __access_ok
+/*
+ * 'size' is a compile-time constant for most callers, so optimize for
+ * this case to turn the check into a single comparison against a constant
+ * limit and catch all possible overflows.
+ * On architectures with separate user address space (m68k, s390, parisc,
+ * sparc64) or those without an MMU, this should always return true.
+ *
+ * This version was originally contributed by Jonas Bonn for the
+ * OpenRISC architecture, and was found to be the most efficient
+ * for constant 'size' and 'limit' values.
+ */
+static inline int __access_ok(const void __user *ptr, unsigned long size)
+{
+	unsigned long limit = user_addr_max();
+	unsigned long addr = (unsigned long)ptr;
+
+	if (IS_ENABLED(CONFIG_ALTERNATE_USER_ADDRESS_SPACE))
+		return true;
+
+	return (size <= limit) && (addr <= (limit - size));
+}
+#endif
+
+#ifndef access_ok
+#define access_ok(addr, size) likely(__access_ok(addr, size))
+#endif
+
+#endif
diff --git a/include/asm-generic/uaccess.h b/include/asm-generic/uaccess.h
index 0870fa11a7c5..ebc685dc8d74 100644
--- a/include/asm-generic/uaccess.h
+++ b/include/asm-generic/uaccess.h
@@ -114,28 +114,9 @@ static inline void set_fs(mm_segment_t fs)
 }
 #endif
 
-#ifndef uaccess_kernel
-#define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
-#endif
-
-#ifndef user_addr_max
-#define user_addr_max() (uaccess_kernel() ? ~0UL : TASK_SIZE)
-#endif
-
 #endif /* CONFIG_SET_FS */
 
-#define access_ok(addr, size) __access_ok((unsigned long)(addr),(size))
-
-/*
- * The architecture should really override this if possible, at least
- * doing a check on the get_fs()
- */
-#ifndef __access_ok
-static inline int __access_ok(unsigned long addr, unsigned long size)
-{
-	return 1;
-}
-#endif
+#include <asm-generic/access_ok.h>
 
 /*
  * These are the main single-value transfer routines.  They automatically
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
index 67e9bc94dc40..2c31667e62e0 100644
--- a/include/linux/uaccess.h
+++ b/include/linux/uaccess.h
@@ -33,13 +33,6 @@ typedef struct {
 	/* empty dummy */
 } mm_segment_t;
 
-#ifndef TASK_SIZE_MAX
-#define TASK_SIZE_MAX			TASK_SIZE
-#endif
-
-#define uaccess_kernel()		(false)
-#define user_addr_max()			(TASK_SIZE_MAX)
-
 static inline mm_segment_t force_uaccess_begin(void)
 {
 	return (mm_segment_t) { };
-- 
2.29.2