Roland McGrath <[EMAIL PROTECTED]> wrote: > What I meant to suggest is that I would start from a safety point of view > with get_user_pages/access_process_vm refusing to do force&&write to > MAP_PRIVATE pages that are in fact being shared (ETXTBSY or something).
That's a good idea. The other possibility I've thought of is maintaining a list of the changes made to such a region and deapplying them / reapplying them as the processes get scheduled. That's probably fine as long as it's just a few breakpoints and it's a single-CPU system. But this is irrelevant as it doesn't address the sharing-prevention issue. > (When it's not being shared, it should do whatever is necessary to make sure > that page is known dirty and not hand it out for later mappings.) NOMMU doesn't with pages at this level, but deals with regions of memory instead. A mapping may be part of a page, a whole page, or several pages. NOMMU private file mmap() allocates using kmalloc(), so if you allocate a 1-byte buffer, that's all you're guaranteed to get. As it happens, when the code sees PT_PTRACED, the VMA is marked as being unshareable by the simple expedient of turning off VM_MAYSHARE, meaning that it neither shares with already existing mappings, nor will it be shareable by mappings that have yet to be made - even within the same process. > Then you can go about trying to make the safe (no sharing) case come about > when you want it. Which brings us back to the if-statement you objected to. Its presence is still required so as to prevent sharing of the executable and loader, and this seems a good a way to do it as any as far as I can see. Remember that it has be controlled by something that can be set before the binfmt load_binary() op runs. David - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
