Re: RO/NX Protections and Modules

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On 01/23/2012 02:04 PM, Dannie Stanley wrote:
> Regarding the source code for kernel version 2.6.38. In
> kernel/module.c the function defined as:
>     SYSCALL_DEFINE3(init_module...)
> Calls set_section_ro_nx for core and init. My first question is this:
>    Q1: Why doesn't the exit text/data get the RO/NX page protection?

I guess this is a trade off.

> In the set_section_ro_nx function the RO comment reads: "Do not
> protect last partial page" and the NX comment reads: "Do not protect
> first partial page." In the presence of mixed pages this makes sense.
> However, change_page_attr_set_clr seems to check for page alignment.
> So my second question is this:
>    Q2: Does the RO/NX only apply to page aligned sections?

Most MMUs/TLBs deal only with page sized memory. They handle access 
attributes in page sized memory.

> Thank you,
> Dannie


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