On Thu, Aug 01, 2024 at 05:08:32PM +0000, jeffxu@xxxxxxxxxxxx wrote: > From: Jeff Xu <jeffxu@xxxxxxxxxxxx> > > In load_elf_binary as part of the execve(), when the current > task’s personality has MMAP_PAGE_ZERO set, the kernel allocates > one page at address 0. According to the comment: > > /* Why this, you ask??? Well SVr4 maps page 0 as read-only, > and some applications "depend" upon this behavior. > Since we do not have the power to recompile these, we > emulate the SVr4 behavior. Sigh. */ > > At one point, Linus suggested removing this [1]. For users, I didn't find much in a Debian Code Search: https://codesearch.debian.net/search?q=MMAP_PAGE_ZERO&literal=1&perpkg=1 I see rr uses it in testing, and some utils have it as an option, so I think maybe just leave it supported. > > Sealing this is probably safe, the comment doesn’t say > the app ever wanting to change the mapping to rwx. Sealing > also ensures that never happens. Yeah, this seems fine to me. > > [1] https://lore.kernel.org/lkml/CAHk-=whVa=nm_GW=NVfPHqcxDbWt4JjjK1YWb0cLjO4ZSGyiDA@xxxxxxxxxxxxxx/ > > Jeff Xu (1): > binfmt_elf: mseal address zero > > fs/binfmt_elf.c | 4 ++++ > include/linux/mm.h | 4 ++++ > mm/mseal.c | 2 +- > 3 files changed, 9 insertions(+), 1 deletion(-) > > -- > 2.46.0.rc1.232.g9752f9e123-goog > -- Kees Cook
