2017-06-28 1:07 GMT+02:00 Kees Cook <keescook@xxxxxxxxxxxx>: > On Thu, Jun 15, 2017 at 9:42 AM, Salvatore Mesoraca > <s.mesoraca16@xxxxxxxxx> wrote: >> Creation of a new hook to let LSM modules handle user-space pagefaults on >> x86. >> It can be used to avoid segfaulting the originating process. >> If it's the case it can modify process registers before returning. >> This is not a security feature by itself, it's a way to soften some >> unwanted side-effects of restrictive security features. >> In particular this is used by S.A.R.A. can be used to implement what >> PaX call "trampoline emulation" that, in practice, allow for some specific >> code sequences to be executed even if they are in non executable memory. >> This may look like a bad thing at first, but you have to consider >> that: >> - This allows for strict memory restrictions (e.g. W^X) to stay on even >> when they should be turned off. And, even if this emulation >> makes those features less effective, it's still better than having >> them turned off completely. >> - The only code sequences emulated are trampolines used to make >> function calls. In many cases, when you have the chance to >> make arbitrary memory writes, you can already manipulate the >> control flow of the program by overwriting function pointers or >> return values. So, in many cases, the "trampoline emulation" >> doesn't introduce new exploit vectors. >> - It's a feature that can be turned on only if needed, on a per >> executable file basis. > > Can this be made arch-agnostic? It seems a per-arch register-handling > routine would be needed, though. :( S.A.R.A.'s "pagefault_handler_x86" implementation is fully arch specific so it won't benefit too much from this change. Anyway having a single hook for all archs is probably a cleaner solution, I'll change it in the v3. Would it be OK if I make it arch-agnostic while I actually keep it only in arch/x86/mm/fault.c? Thank you for your help. Salvatore -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
