From 168b84d5d2c07ae6c96ea40a7f420b5b525defa0 Mon Sep 17 00:00:00 2001 From: Paul Burton Date: Sat, 9 Feb 2019 19:47:36 +0000 Subject: [PATCH] MIPS: Fix access_ok() for the last byte of user space MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit The MIPS implementation of access_ok() incorrectly reports that access to the final byte of user memory is not OK, much as the alpha & SH versions did prior to commit 94bd8a05cd4d ("Fix 'acccess_ok()' on alpha and SH"). For example on a MIPS64 system with __UA_LIMIT == 0xffff000000000000 we incorrectly fail in the following cases: access_ok(0xffffffffffff, 0x1) = 0 access_ok(0xfffffffffffe, 0x2) = 0 Fix MIPS in the same way as alpha & SH, by subtracting one from the addr + size condition when size is non-zero. With this the access_ok() calls above return 1 indicating that the access may be valid. The cost of the improved check is pretty minimal - we gain 2410 bytes, or 0.03%, in kernel code size for a 64r6el_defconfig kernel built using GCC 8.1.0. Signed-off-by: Paul Burton Reported-by: Linus Torvalds Reviewed-by: Philippe Mathieu-Daudé Signed-off-by: Thomas Bogendoerfer --- arch/mips/include/asm/uaccess.h | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/arch/mips/include/asm/uaccess.h b/arch/mips/include/asm/uaccess.h index 9e9e3aa9c341..ab47e597656a 100644 --- a/arch/mips/include/asm/uaccess.h +++ b/arch/mips/include/asm/uaccess.h @@ -79,7 +79,9 @@ extern u64 __ua_limit; static inline int __access_ok(const void __user *p, unsigned long size) { unsigned long addr = (unsigned long)p; - return (__UA_LIMIT & (addr | (addr + size) | __ua_size(size))) == 0; + unsigned long end = addr + size - !!size; + + return (__UA_LIMIT & (addr | end | __ua_size(size))) == 0; } #define access_ok(addr, size) \