Hi, Please don't backport this change. While it has been tested, it's a process memory layout change, and I'd like to be as conservative as possible about it. If there is fall-out, I'd prefer to keep it limited to 6.10+. :) -Kees On May 26, 2024 2:41:44 AM PDT, Sasha Levin <sashal@xxxxxxxxxx> wrote: >From: Kees Cook <keescook@xxxxxxxxxxxx> > >[ Upstream commit 2a5eb9995528441447d33838727f6ec1caf08139 ] > >Currently the brk starts its randomization immediately after .bss, >which means there is a chance that when the random offset is 0, linear >overflows from .bss can reach into the brk area. Leave at least a single >page gap between .bss and brk (when it has not already been explicitly >relocated into the mmap range). > >Reported-by: <y0un9n132@xxxxxxxxx> >Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7ayCbu0MPJTZzWkw@xxxxxxxxxxxxxx/ >Link: https://lore.kernel.org/r/20240217062545.1631668-2-keescook@xxxxxxxxxxxx >Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> >Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> >--- > fs/binfmt_elf.c | 3 +++ > 1 file changed, 3 insertions(+) > >diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c >index 5397b552fbeb5..7862962f7a859 100644 >--- a/fs/binfmt_elf.c >+++ b/fs/binfmt_elf.c >@@ -1262,6 +1262,9 @@ static int load_elf_binary(struct linux_binprm *bprm) > if (IS_ENABLED(CONFIG_ARCH_HAS_ELF_RANDOMIZE) && > elf_ex->e_type == ET_DYN && !interpreter) { > mm->brk = mm->start_brk = ELF_ET_DYN_BASE; >+ } else { >+ /* Otherwise leave a gap between .bss and brk. */ >+ mm->brk = mm->start_brk = mm->brk + PAGE_SIZE; > } > > mm->brk = mm->start_brk = arch_randomize_brk(mm); -- Kees Cook
