Recently, Google Project Zero discovered several classes of attack against speculative execution. One of these, known as variant-1, allows explicit bounds checks to be bypassed under speculation, providing an arbitrary read gadget. Further details can be found on the GPZ blog [1] and the Documentation patch in this series. There are a number of potential gadgets in the Linux codebase, and mitigations for these are architecture-specific. This RFC attempts to provide a cross-architecture API for inhibiting these primitives. Hopefully, architecture-specific mitigations can be unified behind this. An arm64 implementation is provided following the architecturally recommended sequence laid out in the Arm whitepaper [2]. The API is based on a proposed compiler intrinsic [3]. I've provided a patch to BPF as an example use of the API. I know that this is incomplete and less than optimal. I'd appreciate feedback from other affected architectures as to whether this API is suitable for their required mitigation. I've pushed the series to my kernel.org repo [4]. Since v1 [5]: * Remove the nospec_*load helpers * Added nospec_array_ptr() * Rework asm-generic implementation to fit other architectures * Improve documentation [1] https://googleprojectzero.blogspot.co.uk/2018/01/reading-privileged-memory-with-side.html [2] https://developer.arm.com/support/security-update [3] https://developer.arm.com/support/security-update/compiler-support-for-mitigations [4] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git core/nospec [5] https://lkml.kernel.org/r/20180103223827.39601-1-mark.rutland@xxxxxxx Thanks, Mark. Mark Rutland (4): asm-generic/barrier: add generic nospec helpers Documentation: document nospec helpers arm64: implement nospec_{load,ptr}() bpf: inhibit speculated out-of-bounds pointers Documentation/speculation.txt | 166 +++++++++++++++++++++++++++++++++++++++ arch/arm64/include/asm/barrier.h | 55 +++++++++++++ include/asm-generic/barrier.h | 68 ++++++++++++++++ kernel/bpf/arraymap.c | 20 +++-- kernel/bpf/cpumap.c | 5 +- kernel/bpf/devmap.c | 3 +- kernel/bpf/sockmap.c | 3 +- 7 files changed, 308 insertions(+), 12 deletions(-) create mode 100644 Documentation/speculation.txt -- 2.11.0
