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mm/maccess.c
3.05 KB
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/* * Access kernel memory without faulting. */ |
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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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/** * probe_kernel_read(): safely attempt to read from a location * @dst: pointer to the buffer that shall take the data * @src: address to read from * @size: size of the data chunk * * Safely read from address @src to the buffer at @dst. If a kernel fault * happens, handle that and return -EFAULT. |
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* * We ensure that the copy_from_user is executed in atomic context so that * do_page_fault() doesn't attempt to take mmap_sem. This makes * probe_kernel_read() suitable for use within regions where the caller * already holds mmap_sem, or other locks which nest inside mmap_sem. |
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*/ |
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long __weak probe_kernel_read(void *dst, const void *src, size_t size) |
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__attribute__((alias("__probe_kernel_read"))); |
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long __probe_kernel_read(void *dst, const void *src, size_t size) |
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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(); ret = __copy_from_user_inatomic(dst, (__force const void __user *)src, size); pagefault_enable(); |
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set_fs(old_fs); |
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return ret ? -EFAULT : 0; } EXPORT_SYMBOL_GPL(probe_kernel_read); /** * probe_kernel_write(): safely attempt to write to a location * @dst: address to write to * @src: pointer to the data that shall be written * @size: size of the data chunk * * Safely write to address @dst from the buffer at @src. If a kernel fault * happens, handle that and return -EFAULT. */ |
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long __weak probe_kernel_write(void *dst, const void *src, size_t size) |
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__attribute__((alias("__probe_kernel_write"))); |
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long __probe_kernel_write(void *dst, const void *src, size_t size) |
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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(); ret = __copy_to_user_inatomic((__force void __user *)dst, src, size); pagefault_enable(); |
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set_fs(old_fs); |
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return ret ? -EFAULT : 0; } EXPORT_SYMBOL_GPL(probe_kernel_write); |
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/** * strncpy_from_unsafe: - Copy a NUL terminated string from unsafe address. * @dst: Destination address, in kernel space. This buffer must be at * least @count bytes long. * @src: Unsafe address. * @count: Maximum number of bytes to copy, including the trailing NUL. * * Copies a NUL-terminated string from unsafe address to kernel buffer. * * On success, returns the length of the string INCLUDING the trailing NUL. * * If access fails, returns -EFAULT (some data may have been copied * and the trailing NUL added). * * If @count is smaller than the length of the string, copies @count-1 bytes, * sets the last byte of @dst buffer to NUL and returns @count. */ long strncpy_from_unsafe(char *dst, const void *unsafe_addr, long count) { mm_segment_t old_fs = get_fs(); const void *src = unsafe_addr; long ret; if (unlikely(count <= 0)) return 0; set_fs(KERNEL_DS); pagefault_disable(); 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); dst[-1] = '\0'; pagefault_enable(); set_fs(old_fs); |
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return ret ? -EFAULT : src - unsafe_addr; |
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} |