| Message ID | 20240801170838.356177-1-jeffxu@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | binfmt_elf: seal address zero | expand |
On Thu, Aug 01, 2024 at 05:08:32PM +0000, jeffxu@chromium.org wrote: > From: Jeff Xu <jeffxu@chromium.org> > > 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@mail.gmail.com/ > > 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 >
From: Jeff Xu <jeffxu@chromium.org> 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]. 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. [1] https://lore.kernel.org/lkml/CAHk-=whVa=nm_GW=NVfPHqcxDbWt4JjjK1YWb0cLjO4ZSGyiDA@mail.gmail.com/ 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(-)