On Tue, Feb 27, 2018 at 11:01:23AM +0100, Florian Weimer wrote: > I think it would be a nice addition to the toolchain if it were > possible to programatically initialize data in the RELRO section. > We do this in glibc, but I don't think this is currently supported > for general use. > > One important application is to allocate a memory region with mmap, > on which protection flags can be changed as needed. This way, the > application can have a read-only path to its own configuration data, > for example. > > Do you think this would be worthwhile to implement? Any suggestions > how we should do it, without needing binutils/GCC/glibc updates?
This weakens protection of the actual relro section (because there's a window where it's writable but application code is running; in the case of thread creation from ctors, or dlopen in a multithreaded program, this is a nontrivial window) and has no benefit, except saving a page of memory, over the application just calling mprotect itself. If the application already has to annotate that the data is going to be read-only after ctors, it can just page-align/page-pad the data itself and call mprotect with minimal additional effort, and no complex interaction between application code and relro (which is about RELocations not arbitrary data protection). Rich
