From 92ae03f2ef99fbc23bfa9080d6b58f25227bd7ef Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Fri, 6 Apr 2012 14:32:32 -0700 Subject: x86: merge 32/64-bit versions of 'strncpy_from_user()' and speed it up This merges the 32- and 64-bit versions of the x86 strncpy_from_user() by just rewriting it in C rather than the ancient inline asm versions that used lodsb/stosb and had been duplicated for (trivial) differences between the 32-bit and 64-bit versions. While doing that, it also speeds them up by doing the accesses a word at a time. Finally, the new routines also properly handle the case of hitting the end of the address space, which we have never done correctly before (fs/namei.c has a hack around it for that reason). Despite all these improvements, it actually removes more lines than it adds, due to the de-duplication. Also, we no longer export (or define) the legacy __strncpy_from_user() function (that was defined to not do the user permission checks), since it's not actually used anywhere, and the user address space checks are built in to the new code. Other architecture maintainers have been notified that the old hack in fs/namei.c will be going away in the 3.5 merge window, in case they copied the x86 approach of being a bit cavalier about the end of the address space. Cc: linux-arch@vger.kernel.org Cc: Ingo Molnar Cc: Peter Anvin" Signed-off-by: Linus Torvalds --- arch/x86/lib/usercopy.c | 103 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 103 insertions(+) (limited to 'arch/x86/lib/usercopy.c') diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c index 97be9cb54483..57252c928f56 100644 --- a/arch/x86/lib/usercopy.c +++ b/arch/x86/lib/usercopy.c @@ -7,6 +7,8 @@ #include #include +#include + /* * best effort, GUP based copy_from_user() that is NMI-safe */ @@ -41,3 +43,104 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n) return len; } EXPORT_SYMBOL_GPL(copy_from_user_nmi); + +static inline unsigned long count_bytes(unsigned long mask) +{ + mask = (mask - 1) & ~mask; + mask >>= 7; + return count_masked_bytes(mask); +} + +/* + * Do a strncpy, return length of string without final '\0'. + * 'count' is the user-supplied count (return 'count' if we + * hit it), 'max' is the address space maximum (and we return + * -EFAULT if we hit it). + */ +static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, long max) +{ + long res = 0; + + /* + * Truncate 'max' to the user-specified limit, so that + * we only have one limit we need to check in the loop + */ + if (max > count) + max = count; + + while (max >= sizeof(unsigned long)) { + unsigned long c; + + /* Fall back to byte-at-a-time if we get a page fault */ + if (unlikely(__get_user(c,(unsigned long __user *)(src+res)))) + break; + /* This can write a few bytes past the NUL character, but that's ok */ + *(unsigned long *)(dst+res) = c; + c = has_zero(c); + if (c) + return res + count_bytes(c); + res += sizeof(unsigned long); + max -= sizeof(unsigned long); + } + + while (max) { + char c; + + if (unlikely(__get_user(c,src+res))) + return -EFAULT; + dst[res] = c; + if (!c) + return res; + res++; + max--; + } + + /* + * Uhhuh. We hit 'max'. But was that the user-specified maximum + * too? If so, that's ok - we got as much as the user asked for. + */ + if (res >= count) + return count; + + /* + * Nope: we hit the address space limit, and we still had more + * characters the caller would have wanted. That's an EFAULT. + */ + return -EFAULT; +} + +/** + * strncpy_from_user: - Copy a NUL terminated string from userspace. + * @dst: Destination address, in kernel space. This buffer must be at + * least @count bytes long. + * @src: Source address, in user space. + * @count: Maximum number of bytes to copy, including the trailing NUL. + * + * Copies a NUL-terminated string from userspace to kernel space. + * + * On success, returns the length of the string (not including the trailing + * NUL). + * + * If access to userspace fails, returns -EFAULT (some data may have been + * copied). + * + * If @count is smaller than the length of the string, copies @count bytes + * and returns @count. + */ +long +strncpy_from_user(char *dst, const char __user *src, long count) +{ + unsigned long max_addr, src_addr; + + if (unlikely(count <= 0)) + return 0; + + max_addr = current_thread_info()->addr_limit.seg; + src_addr = (unsigned long)src; + if (likely(src_addr < max_addr)) { + unsigned long max = max_addr - src_addr; + return do_strncpy_from_user(dst, src, count, max); + } + return -EFAULT; +} +EXPORT_SYMBOL(strncpy_from_user); -- cgit v1.2.3 From 12e993b89464707398e4209bd99983e376454985 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Sun, 15 Apr 2012 17:23:00 -0700 Subject: x86-32: fix up strncpy_from_user() sign error The 'max' range needs to be unsigned, since the size of the user address space is bigger than 2GB. We know that 'count' is positive in 'long' (that is checked in the caller), so we will truncate 'max' down to something that fits in a signed long, but before we actually do that, that comparison needs to be done in unsigned. Bug introduced in commit 92ae03f2ef99 ("x86: merge 32/64-bit versions of 'strncpy_from_user()' and speed it up"). On x86-64 you can't trigger this, since the user address space is much smaller than 63 bits, and on x86-32 it works in practice, since you would seldom hit the strncpy limits anyway. I had actually tested the corner-cases, I had only tested them on x86-64. Besides, I had only worried about the case of a pointer *close* to the end of the address space, rather than really far away from it ;) This also changes the "we hit the user-specified maximum" to return 'res', for the trivial reason that gcc seems to generate better code that way. 'res' and 'count' are the same in that case, so it really doesn't matter which one we return. Signed-off-by: Linus Torvalds --- arch/x86/lib/usercopy.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) (limited to 'arch/x86/lib/usercopy.c') diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c index 57252c928f56..d6ae30bbd7bb 100644 --- a/arch/x86/lib/usercopy.c +++ b/arch/x86/lib/usercopy.c @@ -57,7 +57,7 @@ static inline unsigned long count_bytes(unsigned long mask) * hit it), 'max' is the address space maximum (and we return * -EFAULT if we hit it). */ -static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, long max) +static inline long do_strncpy_from_user(char *dst, const char __user *src, long count, unsigned long max) { long res = 0; @@ -100,7 +100,7 @@ static inline long do_strncpy_from_user(char *dst, const char __user *src, long * too? If so, that's ok - we got as much as the user asked for. */ if (res >= count) - return count; + return res; /* * Nope: we hit the address space limit, and we still had more -- cgit v1.2.3