diff options
| -rw-r--r-- | include/linux/uaccess.h | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h index 391e7ed1eb3f..a48d7f11c7be 100644 --- a/include/linux/uaccess.h +++ b/include/linux/uaccess.h @@ -19,4 +19,26 @@ static inline unsigned long __copy_from_user_nocache(void *to, #endif /* ARCH_HAS_NOCACHE_UACCESS */ +/** + * probe_kernel_address(): safely attempt to read from a location + * @addr: address to read from - its type is type typeof(retval)* + * @retval: read into this variable + * + * Safely read from address @addr into variable @revtal. If a kernel fault + * happens, handle that and return -EFAULT. + * We ensure that the __get_user() is executed in atomic context so that + * do_page_fault() doesn't attempt to take mmap_sem. This makes + * probe_kernel_address() suitable for use within regions where the caller + * already holds mmap_sem, or other locks which nest inside mmap_sem. + */ +#define probe_kernel_address(addr, retval) \ + ({ \ + long ret; \ + \ + inc_preempt_count(); \ + ret = __get_user(retval, addr); \ + dec_preempt_count(); \ + ret; \ + }) + #endif /* __LINUX_UACCESS_H__ */ |