v4: - rebase to v5.8-rc2 v3: https://lore.kernel.org/lkml/20200406231606.37619-1-keescook@xxxxxxxxxxxx/ v2: https://lore.kernel.org/lkml/20200324203231.64324-1-keescook@xxxxxxxxxxxx/ rfc: https://lore.kernel.org/kernel-hardening/20190329081358.30497-1-elena.reshetova@xxxxxxxxx/ Hi, This is a continuation and refactoring of Elena's earlier effort to add kernel stack base offset randomization. In the time since the previous discussions, two attacks[1][2] were made public that depended on stack determinism, so we're no longer in the position of "this is a good idea but we have no examples of attacks". :) Earlier discussions also devolved into debates on entropy sources, which is mostly a red herring, given the already low entropy available due to stack size. Regardless, entropy can be changed/improved separately from this series as needed. Earlier discussions also got stuck debating how much syscall overhead was too much, but this is also a red herring since the feature itself needs to be selectable at boot with no cost for those that don't want it: this is solved here with static branches. So, here is an improved version, made as arch-agnostic as possible, with usage added for x86 and arm64. It also includes some small static branch clean ups, and addresses some surprise performance issues due to the stack canary[3]. Note that for v5.8, this depends on this fix (due to how x86 changed its stack protector removal for syscall entry): https://lore.kernel.org/lkml/202006221201.3641ED037E@keescook/ Thanks! -Kees [1] https://a13xp0p0v.github.io/2020/02/15/CVE-2019-18683.html [2] https://repositorio-aberto.up.pt/bitstream/10216/125357/2/374717.pdf [3] https://lore.kernel.org/lkml/202003281520.A9BFF461@keescook/ Kees Cook (5): jump_label: Provide CONFIG-driven build state defaults init_on_alloc: Unpessimize default-on builds stack: Optionally randomize kernel stack offset each syscall x86/entry: Enable random_kstack_offset support arm64: entry: Enable random_kstack_offset support Makefile | 4 ++++ arch/Kconfig | 23 ++++++++++++++++++ arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 5 ++++ arch/arm64/kernel/syscall.c | 10 ++++++++ arch/x86/Kconfig | 1 + arch/x86/entry/common.c | 11 +++++++++ include/linux/jump_label.h | 19 +++++++++++++++ include/linux/mm.h | 18 +++++--------- include/linux/randomize_kstack.h | 40 ++++++++++++++++++++++++++++++++ init/main.c | 23 ++++++++++++++++++ mm/page_alloc.c | 12 ++-------- 12 files changed, 145 insertions(+), 22 deletions(-) create mode 100644 include/linux/randomize_kstack.h -- 2.25.1
