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].
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@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
