On Wed, Oct 05, 2022 at 07:54:41AM -0600, Theo de Raadt wrote: > Marc Espie <es...@nerim.net> wrote: > > > On Tue, Oct 04, 2022 at 10:15:51AM -0600, Theo de Raadt wrote: > > > A note on why this chance is coming. > > > > > > malloc.c (as it is today), does mprotects back and forth between RW and > > > R, to protect an internal object. This object is in bss, it is not > > > allocated with mmap. With the upcoming mimmutable change, the bss will > > > become immutable by default, at program load time. mimmutable even > > > prevents > > > changing a RW object to R. > > > > I'm probably missing something here, but for me, traditionally, > > BSS is the "set to 0" section of global variables of a program... which are > > usually going to be changed to some other value. > > > > Or are we talking at cross purposes ? > > If you read the mimmutable diff, it has a manual page, and the answer is in > there.
Ah my mistake, I read a bit fast, and I thought the *pages* themselves were immutable. Stupid question time: is there any reason not to allow further changes that would *restrict* the pages further ? A bit like pledge works. Like, say you mark a region "immutable" with RW rights, then later on use mprotect to mark it down RO, and you can never get back ?
