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@kernel.org wrote:
From: Kees Cook keescook@chromium.org
[ 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@gmail.com Closes: https://lore.kernel.org/linux-hardening/CA+2EKTVLvc8hDZc+2Yhwmus=dzOUG5E4gV7... Link: https://lore.kernel.org/r/20240217062545.1631668-2-keescook@chromium.org Signed-off-by: Kees Cook keescook@chromium.org Signed-off-by: Sasha Levin sashal@kernel.org
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);