Hi all, This patch series implements something along the lines of KAISER for arm64:
https://gruss.cc/files/kaiser.pdf although I wrote this from scratch because the paper has some funny assumptions about how the architecture works. There is a patch series in review for x86, which follows a similar approach: http://lkml.kernel.org/r/<20171110193058.beca7...@viggo.jf.intel.com> and the topic was recently covered by LWN (currently subscriber-only): https://lwn.net/Articles/738975/ The basic idea is that transitions to and from userspace are proxied through a trampoline page which is mapped into a separate page table and can switch the full kernel mapping in and out on exception entry and exit respectively. This is a valuable defence against various KASLR and timing attacks, particularly as the trampoline page is at a fixed virtual address and therefore the kernel text can be randomized independently. The major consequences of the trampoline are: * We can no longer make use of global mappings for kernel space, so each task is assigned two ASIDs: one for user mappings and one for kernel mappings * Our ASID moves into TTBR1 so that we can quickly switch between the trampoline and kernel page tables * Switching TTBR0 always requires use of the zero page, so we can dispense with some of our errata workaround code. * entry.S gets more complicated to read The performance hit from this series isn't as bad as I feared: things like cyclictest and kernbench seem to be largely unaffected, although syscall micro-benchmarks appear to show that syscall overhead is roughly doubled, and this has an impact on things like hackbench which exhibits a ~10% hit due to its heavy context-switching. Patches based on 4.14 and also pushed here: git://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git kaiser Feedback welcome, Will --->8 Will Deacon (18): arm64: mm: Use non-global mappings for kernel space arm64: mm: Temporarily disable ARM64_SW_TTBR0_PAN arm64: mm: Move ASID from TTBR0 to TTBR1 arm64: mm: Remove pre_ttbr0_update_workaround for Falkor erratum #E1003 arm64: mm: Rename post_ttbr0_update_workaround arm64: mm: Fix and re-enable ARM64_SW_TTBR0_PAN arm64: mm: Allocate ASIDs in pairs arm64: mm: Add arm64_kernel_mapped_at_el0 helper using static key arm64: mm: Invalidate both kernel and user ASIDs when performing TLBI arm64: entry: Add exception trampoline page for exceptions from EL0 arm64: mm: Map entry trampoline into trampoline and kernel page tables arm64: entry: Explicitly pass exception level to kernel_ventry macro arm64: entry: Hook up entry trampoline to exception vectors arm64: erratum: Work around Falkor erratum #E1003 in trampoline code arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks arm64: entry: Add fake CPU feature for mapping the kernel at EL0 arm64: makefile: Ensure TEXT_OFFSET doesn't overlap with trampoline arm64: Kconfig: Add CONFIG_UNMAP_KERNEL_AT_EL0 arch/arm64/Kconfig | 30 +++-- arch/arm64/Makefile | 18 ++- arch/arm64/include/asm/asm-uaccess.h | 25 ++-- arch/arm64/include/asm/assembler.h | 27 +---- arch/arm64/include/asm/cpucaps.h | 3 +- arch/arm64/include/asm/kernel-pgtable.h | 12 +- arch/arm64/include/asm/memory.h | 1 + arch/arm64/include/asm/mmu.h | 12 ++ arch/arm64/include/asm/mmu_context.h | 9 +- arch/arm64/include/asm/pgtable-hwdef.h | 1 + arch/arm64/include/asm/pgtable-prot.h | 21 +++- arch/arm64/include/asm/pgtable.h | 1 + arch/arm64/include/asm/proc-fns.h | 6 - arch/arm64/include/asm/tlbflush.h | 16 ++- arch/arm64/include/asm/uaccess.h | 21 +++- arch/arm64/kernel/cpufeature.c | 11 ++ arch/arm64/kernel/entry.S | 195 ++++++++++++++++++++++++++------ arch/arm64/kernel/process.c | 12 +- arch/arm64/kernel/vmlinux.lds.S | 17 +++ arch/arm64/lib/clear_user.S | 2 +- arch/arm64/lib/copy_from_user.S | 2 +- arch/arm64/lib/copy_in_user.S | 2 +- arch/arm64/lib/copy_to_user.S | 2 +- arch/arm64/mm/cache.S | 2 +- arch/arm64/mm/context.c | 36 +++--- arch/arm64/mm/mmu.c | 60 ++++++++++ arch/arm64/mm/proc.S | 12 +- arch/arm64/xen/hypercall.S | 2 +- 28 files changed, 418 insertions(+), 140 deletions(-) -- 2.1.4
