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Re: Encoding page size in the ELF header
- From: fche at redhat dot com (Frank Ch. Eigler)
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: "Carlos O'Donell" <carlos at redhat dot com>, GNU C Library <libc-alpha at sourceware dot org>
- Date: Sat, 26 Sep 2015 19:13:00 -0400
- Subject: Re: Encoding page size in the ELF header
- Authentication-results: sourceware.org; auth=none
- References: <56054662 dot 2010106 at redhat dot com> <56059DD4 dot 1080908 at redhat dot com> <5605A084 dot 4010501 at redhat dot com>
fweimer wrote:
> [...]
>> Can't the application just call getpagesize(), and then use that to
>> decide how to make .data read-only?
>
> The idea is to do something like this:
> #define PAGE_SIZE 4096
> union {
> int critical_data;
> char pad[PAGE_SIZE];
> } u __attribute__((aligned(PAGE_SIZE))) = {};
>
> And then call mprotect(&u, PAGE_SIZE, PROT_READ) after initialization.
Could the app more portably use
int critical_data __attribute__((section(".data.critical")));
and maybe a linker script widgetry to assure padding & fetch
base-addresses, and then mprotect it that way? It would become
independent of page size.
- FChE