v8: - switch to __this_cpu_*() (tglx) - improve commit log details, comments, and masking (ingo, tglx) v7: https://lore.kernel.org/lkml/20210319212835.3928492-1-keescook@xxxxxxxxxxxx/ v6: https://lore.kernel.org/lkml/20210315180229.1224655-1-keescook@xxxxxxxxxxxx/ v5: https://lore.kernel.org/lkml/20210309214301.678739-1-keescook@xxxxxxxxxxxx/ v4: https://lore.kernel.org/lkml/20200622193146.2985288-1-keescook@xxxxxxxxxxxx/ 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 earlier 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 the latest 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]. At the very least, the first two patches can land separately (already Acked and Reviewed), since they're kind of "separate", but introduce macros that are used in the core stack changes. If I can get an Ack from an arm64 maintainer, I think this could all land via -tip to make merging easiest. 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 (6): jump_label: Provide CONFIG-driven build state defaults init_on_alloc: Optimize static branches stack: Optionally randomize kernel stack offset each syscall x86/entry: Enable random_kstack_offset support arm64: entry: Enable random_kstack_offset support lkdtm: Add REPORT_STACK for checking stack offsets .../admin-guide/kernel-parameters.txt | 11 ++++ Makefile | 4 ++ arch/Kconfig | 23 ++++++++ arch/arm64/Kconfig | 1 + arch/arm64/kernel/Makefile | 5 ++ arch/arm64/kernel/syscall.c | 16 ++++++ arch/x86/Kconfig | 1 + arch/x86/entry/common.c | 3 + arch/x86/include/asm/entry-common.h | 16 ++++++ drivers/misc/lkdtm/bugs.c | 17 ++++++ drivers/misc/lkdtm/core.c | 1 + drivers/misc/lkdtm/lkdtm.h | 1 + include/linux/jump_label.h | 19 +++++++ include/linux/mm.h | 10 ++-- include/linux/randomize_kstack.h | 55 +++++++++++++++++++ init/main.c | 23 ++++++++ mm/page_alloc.c | 4 +- mm/slab.h | 6 +- 18 files changed, 208 insertions(+), 8 deletions(-) create mode 100644 include/linux/randomize_kstack.h -- 2.25.1
