linux/mm/maccess.c
Alexei Starovoitov d319f34456 mm: Fix copy_from_user_nofault().
There are several issues with copy_from_user_nofault():

- access_ok() is designed for user context only and for that reason
it has WARN_ON_IN_IRQ() which triggers when bpf, kprobe, eprobe
and perf on ppc are calling it from irq.

- it's missing nmi_uaccess_okay() which is a nop on all architectures
except x86 where it's required.
The comment in arch/x86/mm/tlb.c explains the details why it's necessary.
Calling copy_from_user_nofault() from bpf, [ke]probe without this check is not safe.

- __copy_from_user_inatomic() under CONFIG_HARDENED_USERCOPY is calling
check_object_size()->__check_object_size()->check_heap_object()->find_vmap_area()->spin_lock()
which is not safe to do from bpf, [ke]probe and perf due to potential deadlock.

Fix all three issues. At the end the copy_from_user_nofault() becomes
equivalent to copy_from_user_nmi() from safety point of view with
a difference in the return value.

Reported-by: Hsin-Wei Hung <hsinweih@uci.edu>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Florian Lehner <dev@der-flo.net>
Tested-by: Hsin-Wei Hung <hsinweih@uci.edu>
Tested-by: Florian Lehner <dev@der-flo.net>
Link: https://lore.kernel.org/r/20230410174345.4376-2-dev@der-flo.net
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2023-04-12 17:36:23 -07:00

231 lines
5.9 KiB
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;
}
#define copy_from_kernel_nofault_loop(dst, src, len, type, err_label) \
while (len >= sizeof(type)) { \
__get_kernel_nofault(dst, src, type, err_label); \
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); \
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);