On Tue, Nov 19, 2024 at 10:14:52AM -0500, John Baldwin wrote: > On 11/19/24 22:30, Konstantin Belousov wrote: > > On Thu, Nov 14, 2024 at 09:47:30AM -0500, John Baldwin wrote: > > > On 11/13/24 12:10, Jessica Clarke wrote: > > > > On 13 Nov 2024, at 19:44, John Baldwin <j...@freebsd.org> wrote: > > > > > > > > > > On 4/7/22 07:38, Andrew Turner wrote: > > > > > > The branch main has been updated by andrew: > > > > > > URL: > > > > > > https://cgit.FreeBSD.org/src/commit/?id=e85eaa930862d5b4dc917bc31e8d7254a693635d > > > > > > commit e85eaa930862d5b4dc917bc31e8d7254a693635d > > > > > > Author: Andrew Turner <and...@freebsd.org> > > > > > > AuthorDate: 2022-04-04 15:05:40 +0000 > > > > > > Commit: Andrew Turner <and...@freebsd.org> > > > > > > CommitDate: 2022-04-07 14:37:37 +0000 > > > > > > Have rtld query the page size from the kernel > > > > > > To allow for a dynamic page size on arm64 have the > > > > > > runtime linker > > > > > > query the kernel for the currentl page size. > > > > > > Reviewed by: kib > > > > > > Sponsored by: The FreeBSD Foundation > > > > > > Differential Revision: https://reviews.freebsd.org/D34765 > > > > > > > > > > This broke relro handling for rtld. The reason is that > > > > > init_pagesizes() is > > > > > called after parsing the program headers for rltd in init_rtld(). As > > > > > a result, > > > > > page_size is 0 when rtld_round_page() is called so the relro_size is > > > > > 0. The > > > > > RTLD_INIT_EARLY_PAGESIZES case was for ia64, and in the early case > > > > > it's probably > > > > > not safe to call sysctl? If it is safe to call sysctl, we could just > > > > > always > > > > > init pagesizes early? > > > > > > > > It looks like there are a few things going on: > > > > > > > > 1. relocate_object calls obj_enforce_relro if !obj->mainprog, so will > > > > try to enforce RELRO for RTLD itself whilst page_size is 0 > > > > > > > > 2. init_rtld later calls obj_enforce_relro for obj_rtld, after > > > > page_size has been initialised > > > > > > > > 3. init_rtld is careful to avoid using global variables until it’s > > > > called relocate_objects for RTLD itself, but by hiding accesses to > > > > page_size away in rtld_*_page that’s no longer true (definitely not > > > > true in the case of text relocations, for example, though whether it > > > > also occurs for other cases we care more about I don’t know) > > > > > > > > So I think there are a couple of things to fix: > > > > > > > > 1. Stop accessing page_size prior to relocate_objects returning for > > > > RTLD itself > > > > > > > > 2. Stop enforcing RELRO twice for RTLD (e.g. add && obj != rtldobj to > > > > relocate_object’s case) > > > > > > > > At least, that’s what I’ve inferred from reading the code. > > > > > > > > Though, to be honest, things might be rather nicer if we just made > > > > .rtld_start responsible for relocating RTLD itself prior to calling > > > > init_rtld, that’s what we have to do for CHERI, as do arm, powerpc and > > > > powerpc64, and it means you can use globals from the start in init_rtld. > > > > > > I've done 2) locally which fixed my immediate issue. > > Can you provide some more info please? > > I have a local patch that supports mutiple PT_GNU_RELRO segments, and to > do that it removes relro_* from Obj_Entry and just walks the list of > phdrs in obj_remap_relro(). However, that defeats the order you mention > below of the timing of parse_rtld_phdr(). I hadn't realized until your > paragraph below that that local change was part of why this was exposed. > It would still be more correct, strictly speaking, to skip obj_enforce_relro > for rtldobj, and if we ever supported multiple PT_GNU_RELRO upstream we > would want that change. Ok, please commit this change.
> > I had also missed the later explicit call to obj_enforce_relro() for obj_rtld > when I sent my original e-mail, so nothing is broken in FreeBSD. > > > obj_enforce_relro() only acts if obj_relro_size is > 0, which requires > > the call to parse_rtld_phdr() to fill it. This is indeed called after the > > rtld is relocated by relocate_object(s), but so it was before the Andrew' > > change. > > > > I can see a problem if plt is mapped ro and requires relro to remap it > > rw before relocation, but I do not believe this is the case for rtld and > > any static linker. > > > > And what is the arch? > > I was testing on a CHERI arch since that is my use case for multiple > PT_GNU_RELRO sections, though the change to obj_remap_relro() is applicable > to all architectures. > > > The RTLD_INIT_PAGESIZES_EARLY symbol indeed should be eliminated, I have > > the patch. But let's sort out the page size issue as well. > > I do think we can probably just axe that code entirely. Well, just the #ifdefs. Yes, I will commit it.