linux-kernel - [PATCH 04/14] x86: use more conventional access

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Date:   Mon, 14 Feb 2022 17:34:42 +0100
From:   Arnd Bergmann <arnd@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Christoph Hellwig <hch@....de>, linux-arch@...r.kernel.org,
        linux-mm@...ck.org, linux-api@...r.kernel.org, arnd@...db.de,
        linux-kernel@...r.kernel.org
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        bcain@...eaurora.org, geert@...ux-m68k.org, monstr@...str.eu,
        tsbogend@...ha.franken.de, nickhu@...estech.com,
        green.hu@...il.com, dinguyen@...nel.org, shorne@...il.com,
        deller@....de, mpe@...erman.id.au, peterz@...radead.org,
        mingo@...hat.com, mark.rutland@....com, hca@...ux.ibm.com,
        dalias@...c.org, davem@...emloft.net, richard@....at,
        x86@...nel.org, jcmvbkbc@...il.com, ebiederm@...ssion.com,
        akpm@...ux-foundation.org, ardb@...nel.org,
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        linux-xtensa@...ux-xtensa.org
Subject: [PATCH 04/14] x86: use more conventional access_ok() definition

From: Arnd Bergmann <arnd@...db.de>

The way that access_ok() is defined on x86 is slightly different from
most other architectures, and a bit more complex.

The generic version tends to result in the best output on all
architectures, as it results in single comparison against a constant
limit for calls with a known size.

There are a few callers of __range_not_ok(), all of which use TASK_SIZE
as the limit rather than TASK_SIZE_MAX, but I could not see any reason
for picking this. Changing these to call __access_ok() instead uses the
default limit, but keeps the behavior otherwise.

x86 is the only architecture with a WARN_ON_IN_IRQ() checking
access_ok(), but it's probably best to leave that in place.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 arch/x86/include/asm/uaccess.h | 38 +++++++++++-----------------------
 1 file changed, 12 insertions(+), 26 deletions(-)

diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
index ac96f9b2d64b..6956a63291b6 100644
--- a/arch/x86/include/asm/uaccess.h
+++ b/arch/x86/include/asm/uaccess.h
@@ -16,30 +16,13 @@
  * Test whether a block of memory is a valid user space address.
  * Returns 0 if the range is valid, nonzero otherwise.
  */
-static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, unsigned long limit)
+static inline bool __access_ok(void __user *ptr, unsigned long size)
 {
-	/*
-	 * If we have used "sizeof()" for the size,
-	 * we know it won't overflow the limit (but
-	 * it might overflow the 'addr', so it's
-	 * important to subtract the size from the
-	 * limit, not add it to the address).
-	 */
-	if (__builtin_constant_p(size))
-		return unlikely(addr > limit - size);
-
-	/* Arbitrary sizes? Be careful about overflow */
-	addr += size;
-	if (unlikely(addr < size))
-		return true;
-	return unlikely(addr > limit);
-}
+	unsigned long limit = TASK_SIZE_MAX;
+	unsigned long addr = ptr;
 
-#define __range_not_ok(addr, size, limit)				\
-({									\
-	__chk_user_ptr(addr);						\
-	__chk_range_not_ok((unsigned long __force)(addr), size, limit); \
-})
+	return (size <= limit) && (addr <= (limit - size));
+}
 
 #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
 static inline bool pagefault_disabled(void);
@@ -66,12 +49,15 @@ static inline bool pagefault_disabled(void);
  * Return: true (nonzero) if the memory block may be valid, false (zero)
  * if it is definitely invalid.
  */
-#define access_ok(addr, size)					\
-({									\
-	WARN_ON_IN_IRQ();						\
-	likely(!__range_not_ok(addr, size, TASK_SIZE_MAX));		\
+#define access_ok(addr, size)		\
+({					\
+	WARN_ON_IN_IRQ();		\
+	likely(__access_ok(addr, size));\
 })
 
+#define __range_not_ok(addr, size, limit)	(!__access_ok(addr, size))
+#define __chk_range_not_ok(addr, size, limit)	(!__access_ok((void __user *)addr, size))
+
 extern int __get_user_1(void);
 extern int __get_user_2(void);
 extern int __get_user_4(void);
-- 
2.29.2