PR/57792 CVS commit: src/libexec/ld.elf_so

["Taylor R Campbell" <riastradh%netbsd.org@localhost>]

The following reply was made to PR lib/57792; it has been noted by GNATS.

From: "Taylor R Campbell" <riastradh%netbsd.org@localhost>
To: gnats-bugs%gnats.NetBSD.org@localhost
Cc: 
Subject: PR/57792 CVS commit: src/libexec/ld.elf_so
Date: Fri, 18 Apr 2025 02:16:16 +0000

 Module Name:	src
 Committed By:	riastradh
 Date:		Fri Apr 18 02:16:16 UTC 2025
 
 Modified Files:
 	src/libexec/ld.elf_so: reloc.c rtld.c
 
 Log Message:
 ld.elf_so(1): Defer RELRO a bit for eagerly-bound (-z now) programs.
 
 GNU binutils links programs a little differently if they're eagerly
 bound with -Wl,-z,now.  In particular, the part of the .got relocated
 for ifuncs is covered by the RELRO region in eagerly-bound programs
 (-z now), but not in lazily-bound programs (default).
 
 Presumably this is done under the premise that eagerly-bound programs
 will resolve all ifuncs at startup _before_ mprotecting the main
 object's RELRO region.  But ld.elf_so was mprotecting it first, in
 _rtld_do_copy_relocations, and then resolving ifuncs -- at which the
 memory locations where it tries to write the resolutions will be
 mapped read-only.
 
 (In contrast, for lazily bound programs, ifuncs may also be resolved
 lazily, so the locations they relocate are _not_ covered by the RELRO
 region and we don't run into any trouble)
 
 To avoid this trouble, for eagerly-bound programs, we defer the RELRO
 mprotect of the main object by a little bit -- we move it from
 _rtld_do_copy_relocations to just after _rtld_call_init_functions.
 
 PR lib/57792: SIGSEGV in ld.elf_so / _rtld_call_ifunc
 
 
 To generate a diff of this commit:
 cvs rdiff -u -r1.118 -r1.119 src/libexec/ld.elf_so/reloc.c
 cvs rdiff -u -r1.218 -r1.219 src/libexec/ld.elf_so/rtld.c
 
 Please note that diffs are not public domain; they are subject to the
 copyright notices on the relevant files.