Date: Tue, 19 Nov 2024 08:30:20 +0200 From: Konstantin Belousov <kostikbel@gmail.com> To: John Baldwin <jhb@freebsd.org> Cc: Jessica Clarke <jrtc27@freebsd.org>, Andrew Turner <andrew@freebsd.org>, "src-committers@freebsd.org" <src-committers@freebsd.org>, "dev-commits-src-all@freebsd.org" <dev-commits-src-all@freebsd.org>, "dev-commits-src-main@freebsd.org" <dev-commits-src-main@freebsd.org> Subject: Re: git: e85eaa930862 - main - Have rtld query the page size from the kernel Message-ID: <ZzwwfLvKj-A1T9cU@kib.kiev.ua> In-Reply-To: <4d81d34f-4749-4911-b302-eca9166e4be7@FreeBSD.org> References: <202204071438.237Ecn2A012737@gitrepo.freebsd.org> <92a05dfe-683c-43d9-bd29-3110e89be275@FreeBSD.org> <768D45F9-2F02-4BA1-BFB7-51685486CFCC@freebsd.org> <4d81d34f-4749-4911-b302-eca9166e4be7@FreeBSD.org>
next in thread | previous in thread | raw e-mail | index | archive | help
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 <jhb@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 <andrew@FreeBSD.org> > > > > AuthorDate: 2022-04-04 15:05:40 +0000 > > > > Commit: Andrew Turner <andrew@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? 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? 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 agree though that having all arches implement rtld_relocate_nonplt_self() > which is called before rtld() would be nicer. > > -- > John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?ZzwwfLvKj-A1T9cU>