This series adds support for the ARMv8.3 pointer authentication extension. 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 I've pushed the series to the arm64/pointer-auth branch [2] of my linux tree. I've also pushed out a necessary bootwrapper patch to the pointer-auth branch [3] 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 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. The series only supports the use of an architected algorithm. I've given this some basic testing with a homebrew test suite. More ideally, we'd add some tests to the kernel source tree. I've added some basic KVM support, but this doesn't cater for systems with mismatched support. Looking forward, we'll need ID register emulation in KVM so that we can hide features from guests to cater for such cases. Open questions ============== * Should keys be per-thread rather than per-process? My understanding is that glibc can't (currently) handle threads having different keys, but it might be that another libc would prefer per-thread keys. If desired, we could add a mechanism for a thread to re-initialize its keys without an exec*(). * Do we need a separate hwcap for XPAC* instructions? Library code performing stack unwinding may need to interoperate with other code which may or may not be using pointer authentication. It may be desirable to use XPAC* rather than attempting authentication and/or acquiring the PAC masks via ptrace. As we may expose APIBKey (potentially separately from APIAKey) in future, HWCAP_APIA cannot be used to determine when these instruction can/should be used. * Should we expose a per-process data key now, to go with the insn key? I don't currently have a use-case for this. * Should we expose generic authentication (i.e. APGAKey)? I don't currently have a use-case for this. * Should the kernel remove PACs when unwinding user stacks? This is simple to do, but it's arguably placing a policy in the kernel as to what we expect user stacks to look like. Regardless, userspace will have to perform this when unwinding with DWARF. Thanks, Mark. [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/498941.html [2] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/pointer-auth [3] git://git.kernel.org/pub/scm/linux/kernel/git/mark/boot-wrapper-aarch64.git pointer-auth Mark Rutland (11): arm64: docs: describe ELF hwcaps asm-generic: mm_hooks: allow hooks to be overridden individually arm64: add pointer authentication register bits arm64/cpufeature: add ARMv8.3 id_aa64isar1 bits arm64/cpufeature: detect pointer authentication arm64: Don't trap host pointer auth use to EL2 arm64: add basic pointer authentication support arm64: expose user PAC bit positions via ptrace arm64/kvm: preserve host HCR_EL2 value arm64/kvm: context-switch ptrauth registers arm64: docs: document pointer authentication Documentation/arm64/booting.txt | 8 ++ Documentation/arm64/elf_hwcaps.txt | 138 +++++++++++++++++++++++++ Documentation/arm64/pointer-authentication.txt | 85 +++++++++++++++ arch/arm64/Kconfig | 23 +++++ arch/arm64/include/asm/cpucaps.h | 4 +- arch/arm64/include/asm/esr.h | 3 +- arch/arm64/include/asm/kvm_arm.h | 3 +- arch/arm64/include/asm/kvm_host.h | 28 ++++- arch/arm64/include/asm/kvm_hyp.h | 7 ++ arch/arm64/include/asm/mmu.h | 5 + arch/arm64/include/asm/mmu_context.h | 25 ++++- arch/arm64/include/asm/pointer_auth.h | 97 +++++++++++++++++ arch/arm64/include/asm/sysreg.h | 30 ++++++ arch/arm64/include/uapi/asm/hwcap.h | 1 + arch/arm64/include/uapi/asm/ptrace.h | 5 + arch/arm64/kernel/cpufeature.c | 39 ++++++- arch/arm64/kernel/cpuinfo.c | 1 + arch/arm64/kernel/head.S | 19 +++- arch/arm64/kernel/ptrace.c | 39 +++++++ arch/arm64/kvm/handle_exit.c | 21 ++++ arch/arm64/kvm/hyp/Makefile | 1 + arch/arm64/kvm/hyp/ptrauth-sr.c | 91 ++++++++++++++++ arch/arm64/kvm/hyp/switch.c | 9 +- arch/arm64/kvm/hyp/tlb.c | 6 +- arch/arm64/kvm/sys_regs.c | 32 ++++++ include/asm-generic/mm_hooks.h | 11 ++ include/uapi/linux/elf.h | 1 + 27 files changed, 719 insertions(+), 13 deletions(-) create mode 100644 Documentation/arm64/elf_hwcaps.txt create mode 100644 Documentation/arm64/pointer-authentication.txt create mode 100644 arch/arm64/include/asm/pointer_auth.h create mode 100644 arch/arm64/kvm/hyp/ptrauth-sr.c -- 1.9.1
