This series adds support for the ARMv8.3 pointer authentication extension, enabling userspace return address protection with recent versions of GCC. Since RFC [1]: * Make the KVM context switch (semi-lazy) * Rebase to v4.13-rc1 * Improve pointer authentication documentation * Add hwcap documentation * Various minor cleanups Since v1 [2]: * Rebase to v4.15-rc1 * Settle on per-process keys * Strip PACs when unwinding userspace * Don't expose an XPAC hwcap (this is implied by ID registers) * Leave APIB, ABPDA, APDB, and APGA keys unsupported for now * Support IMP DEF algorithms * Rely on KVM ID register emulation * Various cleanups Since v2 [3]: * Unify HCR_EL2 initialization * s/POINTER_AUTHENTICATION/PTR_AUTH/ * Drop KVM support (for now) * Drop detection of generic authentication While there are use-cases for keys other than APIAKey, the only software that I'm aware of with pointer authentication support is GCC, which only makes use of APIAKey. I'm happy to add support for other keys as users appear. I've pushed the series to the arm64/pointer-auth branch [4] of my linux tree. I've also pushed out a necessary bootwrapper patch to the pointer-auth branch [5] of my bootwrapper repo. Extension Overview ================== The ARMv8.3 pointer authentication extension adds functionality to detect modification of pointer values, mitigating certain classes of attack such as stack smashing, and making return oriented programming attacks harder The extension introduces the concept of a pointer authentication code (PAC), which is stored in some upper bits of pointers. Each PAC is derived from the original pointer, another 64-bit value (e.g. the stack pointer), and a secret 128-bit key. New instructions are added which can be used to: * Insert a PAC into a pointer * Strip a PAC from a pointer * Authenticate strip a PAC from a pointer If authentication succeeds, the code is removed, yielding the original pointer. If authentication fails, bits are set in the pointer such that it is guaranteed to cause a fault if used. These instructions can make use of four keys: * APIAKey (A.K.A. Instruction A key) * APIBKey (A.K.A. Instruction B key) * APDAKey (A.K.A. Data A key) * APDBKey (A.K.A. Data B Key) A subset of these instruction encodings have been allocated from the HINT space, and will operate as NOPs on any ARMv8-A parts which do not feature the extension (or if purposefully disabled by the kernel). Software using only this subset of the instructions should function correctly on all ARMv8-A parts. Additionally, instructions are added to authenticate small blocks of memory in similar fashion, using APGAKey (A.K.A. Generic key). This Series =========== This series enables the use of instructions using APIAKey, which is initialised and maintained per-process (shared by all threads). This series does not add support for APIBKey, APDAKey, APDBKey, nor APGAKey. I've given this some basic testing with a homebrew test suite. More ideally, we'd add some tests to the kernel source tree. For the time being, pointer authentication functionality is hidden from guests via ID register trapping. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/498941.html [2] https://lkml.kernel.org/r/1500480092-28480-1-git-send-email-mark.rutland@xxxxxxx [3] https://lkml.kernel.org/r/20171127163806.31435-1-mark.rutland@xxxxxxx [4] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/pointer-auth [5] git://git.kernel.org/pub/scm/linux/kernel/git/mark/boot-wrapper-aarch64.git pointer-auth Mark Rutland (11): arm64: add pointer authentication register bits arm64/kvm: consistently handle host HCR_EL2 flags arm64/kvm: hide ptrauth from guests arm64: Don't trap host pointer auth use to EL2 arm64/cpufeature: detect pointer authentication asm-generic: mm_hooks: allow hooks to be overridden individually arm64: add basic pointer authentication support arm64: expose user PAC bit positions via ptrace arm64: perf: strip PAC when unwinding userspace arm64: enable pointer authentication arm64: docs: document pointer authentication Documentation/arm64/booting.txt | 8 ++ Documentation/arm64/elf_hwcaps.txt | 6 ++ Documentation/arm64/pointer-authentication.txt | 84 ++++++++++++++++++++ arch/arm64/Kconfig | 23 ++++++ arch/arm64/include/asm/cpucaps.h | 5 +- arch/arm64/include/asm/esr.h | 3 +- arch/arm64/include/asm/kvm_arm.h | 3 + arch/arm64/include/asm/mmu.h | 5 ++ arch/arm64/include/asm/mmu_context.h | 25 +++++- arch/arm64/include/asm/pointer_auth.h | 104 +++++++++++++++++++++++++ arch/arm64/include/asm/sysreg.h | 30 +++++++ arch/arm64/include/uapi/asm/hwcap.h | 1 + arch/arm64/include/uapi/asm/ptrace.h | 7 ++ arch/arm64/kernel/cpufeature.c | 56 +++++++++++++ arch/arm64/kernel/cpuinfo.c | 1 + arch/arm64/kernel/head.S | 5 +- arch/arm64/kernel/perf_callchain.c | 5 +- arch/arm64/kernel/ptrace.c | 38 +++++++++ arch/arm64/kvm/handle_exit.c | 18 +++++ arch/arm64/kvm/hyp/switch.c | 2 +- arch/arm64/kvm/sys_regs.c | 9 +++ include/asm-generic/mm_hooks.h | 11 +++ include/uapi/linux/elf.h | 1 + 23 files changed, 441 insertions(+), 9 deletions(-) create mode 100644 Documentation/arm64/pointer-authentication.txt create mode 100644 arch/arm64/include/asm/pointer_auth.h -- 2.11.0
