109 lines
3.1 KiB
C
109 lines
3.1 KiB
C
/*
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* Access kernel 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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/**
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* probe_kernel_read(): safely attempt to read from a location
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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 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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* 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_sem. This makes
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* probe_kernel_read() suitable for use within regions where the caller
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* 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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{
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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_from_user_inatomic(dst,
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(__force const void __user *)src, size);
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pagefault_enable();
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set_fs(old_fs);
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return ret ? -EFAULT : 0;
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}
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EXPORT_SYMBOL_GPL(probe_kernel_read);
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/**
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* probe_kernel_write(): 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 __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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{
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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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return ret ? -EFAULT : 0;
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}
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EXPORT_SYMBOL_GPL(probe_kernel_write);
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/**
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* strncpy_from_unsafe: - Copy a NUL terminated string from unsafe 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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* @src: 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
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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_unsafe(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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set_fs(KERNEL_DS);
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pagefault_disable();
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do {
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ret = __copy_from_user_inatomic(dst++,
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(const void __user __force *)src++, 1);
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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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