为什么必须使用copy_to_user()/copy_from_user()从内核访问用户空间? [英] Why do you have to use copy_to_user()/copy_from_user() to access user space from the kernel?

问题描述

我很好奇，因为在尝试直接访问内存(然后我发现了这些功能)后出现了内核恐慌.

I'm curious, because I got a kernel panic after trying to access memory directly (then I found these functions).

推荐答案

这些函数可以执行以下操作:

These functions do a few things:

• 他们检查提供的用户空间块是否完全在地址空间(access_ok())的用户部分内-这可以防止用户空间应用程序要求内核读取/写入内核地址；
• 如果无法访问任何地址，它们将返回错误，从而允许将错误返回给用户空间(EFAULT)而不是使内核崩溃(这是通过与页面错误处理程序的特殊协作来实现的，特别是可以检测其中一个用户存储器访问功能何时发生故障)；
• 它们允许使用特定于体系结构的魔术，例如，以确保具有虚拟标记的缓存的体系结构的一致性，禁用诸如SMAP的保护或切换具有单独的用户/内核地址空间(如S/390)的体系结构上的地址空间.

• They check if the supplied userspace block is entirely within the user portion of the address space (access_ok()) - this prevents userspace applications from asking the kernel to read/write kernel addresses;
• They return an error if any of the addresses are inaccessible, allowing the error to be returned to userspace (EFAULT) instead of crashing the kernel (this is implemented by special co-operation with the page fault handler, which specifically can detect when a fault occurs in one of the user memory access functions);
• They allow architecture-specific magic, for example to ensure consistency on architectures with virtually-tagged caches, to disable protections like SMAP or to switch address spaces on architectures with separate user/kernel address spaces like S/390.

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