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![Arnd Bergmann](/assets/img/avatar_default.png)
On machines such as ARMv5 that trap unaligned accesses, these two functions can be slow when each access needs to be emulated, or they might not work at all. Change them so that each loop is only used when both the src and dst pointers are naturally aligned. Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Linus Walleij <linus.walleij@linaro.org> Signed-off-by: Arnd Bergmann <arnd@arndb.de> Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
337 lines
9.1 KiB
C
337 lines
9.1 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Access kernel or user memory without faulting.
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*/
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#include <linux/export.h>
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#include <linux/mm.h>
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#include <linux/uaccess.h>
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bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
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size_t size)
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{
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return true;
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}
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#ifdef HAVE_GET_KERNEL_NOFAULT
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#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
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while (len >= sizeof(type)) { \
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__get_kernel_nofault(dst, src, type, err_label); \
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dst += sizeof(type); \
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src += sizeof(type); \
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len -= sizeof(type); \
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}
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long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
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{
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unsigned long align = 0;
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if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
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align = (unsigned long)dst | (unsigned long)src;
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if (!copy_from_kernel_nofault_allowed(src, size))
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return -ERANGE;
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pagefault_disable();
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if (!(align & 7))
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copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
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if (!(align & 3))
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copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
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if (!(align & 1))
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copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
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copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
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pagefault_enable();
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return 0;
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Efault:
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pagefault_enable();
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return -EFAULT;
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}
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EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
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#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
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while (len >= sizeof(type)) { \
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__put_kernel_nofault(dst, src, type, err_label); \
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dst += sizeof(type); \
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src += sizeof(type); \
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len -= sizeof(type); \
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}
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long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
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{
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unsigned long align = 0;
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if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
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align = (unsigned long)dst | (unsigned long)src;
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pagefault_disable();
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if (!(align & 7))
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copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
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if (!(align & 3))
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copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
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if (!(align & 1))
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copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
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copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
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pagefault_enable();
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return 0;
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Efault:
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pagefault_enable();
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return -EFAULT;
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}
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long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
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{
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const void *src = unsafe_addr;
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if (unlikely(count <= 0))
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return 0;
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if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
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return -ERANGE;
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pagefault_disable();
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do {
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__get_kernel_nofault(dst, src, u8, Efault);
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dst++;
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src++;
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} while (dst[-1] && src - unsafe_addr < count);
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pagefault_enable();
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dst[-1] = '\0';
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return src - unsafe_addr;
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Efault:
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pagefault_enable();
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dst[-1] = '\0';
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return -EFAULT;
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}
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#else /* HAVE_GET_KERNEL_NOFAULT */
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/**
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* copy_from_kernel_nofault(): safely attempt to read from kernel-space
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* @dst: pointer to the buffer that shall take the data
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* @src: address to read from
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* @size: size of the data chunk
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*
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* Safely read from kernel address @src to the buffer at @dst. If a kernel
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* fault happens, handle that and return -EFAULT. If @src is not a valid kernel
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* address, return -ERANGE.
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*
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* We ensure that the copy_from_user is executed in atomic context so that
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* do_page_fault() doesn't attempt to take mmap_lock. This makes
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* copy_from_kernel_nofault() suitable for use within regions where the caller
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* already holds mmap_lock, or other locks which nest inside mmap_lock.
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*/
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long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
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{
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long ret;
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mm_segment_t old_fs = get_fs();
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if (!copy_from_kernel_nofault_allowed(src, size))
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return -ERANGE;
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set_fs(KERNEL_DS);
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pagefault_disable();
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ret = __copy_from_user_inatomic(dst, (__force const void __user *)src,
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size);
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pagefault_enable();
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set_fs(old_fs);
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if (ret)
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);
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/**
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* copy_to_kernel_nofault(): safely attempt to write to a location
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* @dst: address to write to
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* @src: pointer to the data that shall be written
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* @size: size of the data chunk
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*
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* Safely write to address @dst from the buffer at @src. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
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{
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long ret;
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mm_segment_t old_fs = get_fs();
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set_fs(KERNEL_DS);
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pagefault_disable();
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ret = __copy_to_user_inatomic((__force void __user *)dst, src, size);
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pagefault_enable();
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set_fs(old_fs);
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if (ret)
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return -EFAULT;
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return 0;
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}
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/**
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* strncpy_from_kernel_nofault: - Copy a NUL terminated string from unsafe
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* address.
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* @dst: Destination address, in kernel space. This buffer must be at
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* least @count bytes long.
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* @unsafe_addr: Unsafe address.
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* @count: Maximum number of bytes to copy, including the trailing NUL.
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*
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* Copies a NUL-terminated string from unsafe address to kernel buffer.
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*
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* On success, returns the length of the string INCLUDING the trailing NUL.
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*
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* If access fails, returns -EFAULT (some data may have been copied and the
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* trailing NUL added). If @unsafe_addr is not a valid kernel address, return
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* -ERANGE.
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*
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* If @count is smaller than the length of the string, copies @count-1 bytes,
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* sets the last byte of @dst buffer to NUL and returns @count.
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*/
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long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
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{
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mm_segment_t old_fs = get_fs();
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const void *src = unsafe_addr;
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long ret;
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if (unlikely(count <= 0))
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return 0;
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if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
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return -ERANGE;
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set_fs(KERNEL_DS);
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pagefault_disable();
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do {
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ret = __get_user(*dst++, (const char __user __force *)src++);
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} while (dst[-1] && ret == 0 && src - unsafe_addr < count);
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dst[-1] = '\0';
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pagefault_enable();
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set_fs(old_fs);
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return ret ? -EFAULT : src - unsafe_addr;
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}
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#endif /* HAVE_GET_KERNEL_NOFAULT */
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/**
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* copy_from_user_nofault(): safely attempt to read from a user-space location
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* @dst: pointer to the buffer that shall take the data
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* @src: address to read from. This must be a user address.
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* @size: size of the data chunk
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*
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* Safely read from user address @src to the buffer at @dst. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
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{
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long ret = -EFAULT;
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mm_segment_t old_fs = force_uaccess_begin();
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if (access_ok(src, size)) {
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pagefault_disable();
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ret = __copy_from_user_inatomic(dst, src, size);
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pagefault_enable();
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}
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force_uaccess_end(old_fs);
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if (ret)
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(copy_from_user_nofault);
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/**
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* copy_to_user_nofault(): safely attempt to write to a user-space location
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* @dst: address to write to
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* @src: pointer to the data that shall be written
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* @size: size of the data chunk
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*
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* Safely write to address @dst from the buffer at @src. If a kernel fault
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* happens, handle that and return -EFAULT.
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*/
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long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
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{
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long ret = -EFAULT;
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mm_segment_t old_fs = force_uaccess_begin();
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if (access_ok(dst, size)) {
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pagefault_disable();
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ret = __copy_to_user_inatomic(dst, src, size);
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pagefault_enable();
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}
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force_uaccess_end(old_fs);
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if (ret)
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return -EFAULT;
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return 0;
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}
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EXPORT_SYMBOL_GPL(copy_to_user_nofault);
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/**
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* strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
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* address.
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* @dst: Destination address, in kernel space. This buffer must be at
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* least @count bytes long.
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* @unsafe_addr: Unsafe user address.
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* @count: Maximum number of bytes to copy, including the trailing NUL.
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*
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* Copies a NUL-terminated string from unsafe user address to kernel buffer.
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*
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* On success, returns the length of the string INCLUDING the trailing NUL.
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*
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* If access fails, returns -EFAULT (some data may have been copied
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* and the trailing NUL added).
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*
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* If @count is smaller than the length of the string, copies @count-1 bytes,
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* sets the last byte of @dst buffer to NUL and returns @count.
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*/
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long strncpy_from_user_nofault(char *dst, const void __user *unsafe_addr,
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long count)
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{
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mm_segment_t old_fs;
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long ret;
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if (unlikely(count <= 0))
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return 0;
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old_fs = force_uaccess_begin();
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pagefault_disable();
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ret = strncpy_from_user(dst, unsafe_addr, count);
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pagefault_enable();
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force_uaccess_end(old_fs);
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if (ret >= count) {
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ret = count;
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dst[ret - 1] = '\0';
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} else if (ret > 0) {
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ret++;
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}
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return ret;
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}
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/**
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* strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
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* @unsafe_addr: The string to measure.
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* @count: Maximum count (including NUL)
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*
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* Get the size of a NUL-terminated string in user space without pagefault.
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*
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* Returns the size of the string INCLUDING the terminating NUL.
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*
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* If the string is too long, returns a number larger than @count. User
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* has to check the return value against "> count".
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* On exception (or invalid count), returns 0.
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*
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* Unlike strnlen_user, this can be used from IRQ handler etc. because
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* it disables pagefaults.
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*/
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long strnlen_user_nofault(const void __user *unsafe_addr, long count)
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{
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mm_segment_t old_fs;
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int ret;
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old_fs = force_uaccess_begin();
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pagefault_disable();
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ret = strnlen_user(unsafe_addr, count);
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pagefault_enable();
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force_uaccess_end(old_fs);
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return ret;
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}
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