Quelle maccess.c Sprache: C

// SPDX-License-Identifier: GPL-2.0-only
/*
* Access kernel or user memory without faulting.
*/
#include <linux/export.h>
#include <linux/mm.h>
#include <linux/uaccess.h>
#include <asm/tlb.h>

bool __weak copy_from_kernel_nofault_allowed(const void *unsafe_src,
  size_t size)
{
return true;
}

/*
* The below only uses kmsan_check_memory() to ensure uninitialized kernel
* memory isn't leaked.
*/
#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) {     \
  __get_kernel_nofault(dst, src, type, err_label); \
  kmsan_check_memory(src, sizeof(type));   \
  dst += sizeof(type);     \
  src += sizeof(type);     \
  len -= sizeof(type);     \
}

long copy_from_kernel_nofault(void *dst, const void *src, size_t size)
{
unsigned long align = 0;

if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
  align = (unsigned long)dst | (unsigned long)src;

if (!copy_from_kernel_nofault_allowed(src, size))
  return -ERANGE;

pagefault_disable();
if (!(align & 7))
  copy_from_kernel_nofault_loop(dst, src, size, u64, Efault);
if (!(align & 3))
  copy_from_kernel_nofault_loop(dst, src, size, u32, Efault);
if (!(align & 1))
  copy_from_kernel_nofault_loop(dst, src, size, u16, Efault);
copy_from_kernel_nofault_loop(dst, src, size, u8, Efault);
pagefault_enable();
return 0;
Efault:
pagefault_enable();
return -EFAULT;
}
EXPORT_SYMBOL_GPL(copy_from_kernel_nofault);

#define copy_to_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) {     \
  __put_kernel_nofault(dst, src, type, err_label); \
  instrument_write(dst, sizeof(type));   \
  dst += sizeof(type);     \
  src += sizeof(type);     \
  len -= sizeof(type);     \
}

long copy_to_kernel_nofault(void *dst, const void *src, size_t size)
{
unsigned long align = 0;

if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS))
  align = (unsigned long)dst | (unsigned long)src;

pagefault_disable();
if (!(align & 7))
  copy_to_kernel_nofault_loop(dst, src, size, u64, Efault);
if (!(align & 3))
  copy_to_kernel_nofault_loop(dst, src, size, u32, Efault);
if (!(align & 1))
  copy_to_kernel_nofault_loop(dst, src, size, u16, Efault);
copy_to_kernel_nofault_loop(dst, src, size, u8, Efault);
pagefault_enable();
return 0;
Efault:
pagefault_enable();
return -EFAULT;
}

long strncpy_from_kernel_nofault(char *dst, const void *unsafe_addr, long count)
{
const void *src = unsafe_addr;

if (unlikely(count <= 0))
  return 0;
if (!copy_from_kernel_nofault_allowed(unsafe_addr, count))
  return -ERANGE;

pagefault_disable();
do {
  __get_kernel_nofault(dst, src, u8, Efault);
  dst++;
  src++;
} while (dst[-1] && src - unsafe_addr < count);
pagefault_enable();

dst[-1] = '\0';
return src - unsafe_addr;
Efault:
pagefault_enable();
dst[0] = '\0';
return -EFAULT;
}

/**
* copy_from_user_nofault(): safely attempt to read from a user-space location
* @dst: pointer to the buffer that shall take the data
* @src: address to read from. This must be a user address.
* @size: size of the data chunk
*
* Safely read from user address @src to the buffer at @dst. If a kernel fault
* happens, handle that and return -EFAULT.
*/
long copy_from_user_nofault(void *dst, const void __user *src, size_t size)
{
long ret = -EFAULT;

if (!__access_ok(src, size))
  return ret;

if (!nmi_uaccess_okay())
  return ret;

pagefault_disable();
ret = __copy_from_user_inatomic(dst, src, size);
pagefault_enable();

if (ret)
  return -EFAULT;
return 0;
}
EXPORT_SYMBOL_GPL(copy_from_user_nofault);

/**
* copy_to_user_nofault(): safely attempt to write to a user-space 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.
*/
long copy_to_user_nofault(void __user *dst, const void *src, size_t size)
{
long ret = -EFAULT;

if (access_ok(dst, size)) {
  pagefault_disable();
  ret = __copy_to_user_inatomic(dst, src, size);
  pagefault_enable();
}

if (ret)
  return -EFAULT;
return 0;
}
EXPORT_SYMBOL_GPL(copy_to_user_nofault);

/**
* strncpy_from_user_nofault: - Copy a NUL terminated string from unsafe user
* address.
* @dst:   Destination address, in kernel space.  This buffer must be at
*         least @count bytes long.
* @unsafe_addr: Unsafe user address.
* @count: Maximum number of bytes to copy, including the trailing NUL.
*
* Copies a NUL-terminated string from unsafe user 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_user_nofault(char *dst, const void __user *unsafe_addr,
         long count)
{
long ret;

if (unlikely(count <= 0))
  return 0;

pagefault_disable();
ret = strncpy_from_user(dst, unsafe_addr, count);
pagefault_enable();

if (ret >= count) {
  ret = count;
  dst[ret - 1] = '\0';
} else if (ret >= 0) {
  ret++;
}

return ret;
}

/**
* strnlen_user_nofault: - Get the size of a user string INCLUDING final NUL.
* @unsafe_addr: The string to measure.
* @count: Maximum count (including NUL)
*
* Get the size of a NUL-terminated string in user space without pagefault.
*
* Returns the size of the string INCLUDING the terminating NUL.
*
* If the string is too long, returns a number larger than @count. User
* has to check the return value against "> count".
* On exception (or invalid count), returns 0.
*
* Unlike strnlen_user, this can be used from IRQ handler etc. because
* it disables pagefaults.
*/
long strnlen_user_nofault(const void __user *unsafe_addr, long count)
{
int ret;

pagefault_disable();
ret = strnlen_user(unsafe_addr, count);
pagefault_enable();

return ret;
}

void __copy_overflow(int size, unsigned long count)
{
WARN(1, "Buffer overflow detected (%d < %lu)!\n", size, count);
}
EXPORT_SYMBOL(__copy_overflow);

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