| Message ID | 20191211184027.20130-1-catalin.marinas@arm.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | arm64: Memory Tagging Extension user-space support | expand |
On Wed, Dec 11, 2019 at 10:40 AM Catalin Marinas <catalin.marinas@arm.com> wrote: > Hi, > > This series proposes the initial user-space support for the ARMv8.5 > Memory Tagging Extension [1]. Thanks for sending out this series. I have been testing it on Android with the FVP model and my in-development scudo changes that add memory tagging support [1], and have not noticed any problems so far. > - Clarify whether mmap(tagged_addr, PROT_MTE) pre-tags the memory with > the tag given in the tagged_addr hint. Strong justification is > required for this as it would force arm64 to disable the zero page. We would like to use this feature in scudo to tag large (>128KB on Android) allocations, which are currently allocated via mmap rather than from an allocation pool. Otherwise we would need to pay the cost (perf and RSS) of faulting all of their pages at allocation time instead of on demand, if we want to tag them. If we could disable the zero page for tagged mappings only and let the pages be faulted as they are read, that would work for us. Peter [1] https://reviews.llvm.org/D70762
On Fri, Dec 13, 2019 at 10:05:10AM -0800, Peter Collingbourne wrote: > On Wed, Dec 11, 2019 at 10:40 AM Catalin Marinas > <catalin.marinas@arm.com> wrote: > > This series proposes the initial user-space support for the ARMv8.5 > > Memory Tagging Extension [1]. > > Thanks for sending out this series. I have been testing it on Android > with the FVP model and my in-development scudo changes that add memory > tagging support [1], and have not noticed any problems so far. Thanks for the comments so far and the testing. I'll post a v2 next week. > > - Clarify whether mmap(tagged_addr, PROT_MTE) pre-tags the memory with > > the tag given in the tagged_addr hint. Strong justification is > > required for this as it would force arm64 to disable the zero page. > > We would like to use this feature in scudo to tag large (>128KB on > Android) allocations, which are currently allocated via mmap rather > than from an allocation pool. Otherwise we would need to pay the cost > (perf and RSS) of faulting all of their pages at allocation time > instead of on demand, if we want to tag them. Would the default tag of 0 be sufficient here? We disable match-all for user-space already, so 0 is not a wildcard.
Hi, This series proposes the initial user-space support for the ARMv8.5 Memory Tagging Extension [1]. The patches are also available on this branch: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux devel/mte Short description extracted from the MTE whitepaper [2]: MTE aims to increase the memory safety of code written in unsafe languages without requiring source changes, and in some cases, without requiring recompilation. The Arm Memory Tagging Extension implements lock and key access to memory. Locks can be set on memory and keys provided during memory access. If the key matches the lock, the access is permitted. If it does not match, an error is reported. Memory locations are tagged by adding four bits of metadata to each 16 bytes of physical memory. This is the Tag Granule. Tagging memory implements the lock. Pointers, and therefore virtual addresses, are modified to contain the key. In order to implement the key bits without requiring larger pointers MTE uses the Top Byte Ignore (TBI) feature of the ARMv8-A Architecture. When TBI is enabled, the top byte of a virtual address is ignored when using it as an input for address translation. This allows the top byte to store metadata. The rough outline of this series, apart from some clean-up patches: 1. Enable detection of the MTE feature by the kernel. 2. Switch the linear map to use the Normal-Tagged memory attribute so that the kernel can read/write the tags in memory (a.k.a. allocation tags). 3. Handle tags in {clear,copy}_page() and memcmp_pages(). 4. User tag fault exception handling and SIGSEGV injection. 5. PROT_MTE support to enable tag checks/accesses in user-space, together with new arch_calc_vm_flag_bits() and arch_validate_flags() hooks. 6. User control of tag check fault mode and tag exclusion via prctl(), built on top of the PR_{SET,GET}_TAGGED_ADDR_CTRL. 7. Documentation of the user ABI with a C example (though such MTE enabling and allocation tagging is expected to live in a C library). For libc people interested in MTE, I suggest reading the last patch with the ABI documentation. Missing bits before upstreaming: - Swap support. Currently ARM64_MTE (default n) selects ARCH_NO_SWAP. The SPARC ADI hooks for the similar feature are not sufficient for correct (no races) saving and restoring of the MTE metadata in swapped pages. A separate patch series will be posted once implemented. - Related to the above is suspend to disk. - ptrace() support to be able to access the tags in memory of a different process, something like {PEEK,POKE}_TAG. - coredump (user) currently does not contain the tags. - kselftests (work in progress) - Clarify whether mmap(tagged_addr, PROT_MTE) pre-tags the memory with the tag given in the tagged_addr hint. Strong justification is required for this as it would force arm64 to disable the zero page. - Clarify with the hardware architects whether CPUID checking is sufficient or additional description via FDT or ACPI is required. [1] https://community.arm.com/developer/ip-products/processors/b/processors-ip-blog/posts/enhancing-memory-safety [2] https://developer.arm.com/-/media/Arm%20Developer%20Community/PDF/Arm_Memory_Tagging_Extension_Whitepaper.pdf Catalin Marinas (13): kbuild: Add support for 'as-instr' to be used in Kconfig files arm64: alternative: Allow alternative_insn to always issue the first instruction arm64: Use macros instead of hard-coded constants for MAIR_EL1 arm64: mte: Use Normal Tagged attributes for the linear map arm64: mte: Assembler macros and default architecture for .S files arm64: Tags-aware memcmp_pages() implementation mm: Introduce arch_calc_vm_flag_bits() arm64: mte: Add PROT_MTE support to mmap() and mprotect() mm: Introduce arch_validate_flags() arm64: mte: Validate the PROT_MTE request via arch_validate_flags() mm: Allow arm64 mmap(PROT_MTE) on RAM-based files arm64: mte: Allow user control of the tag check mode via prctl() arm64: mte: Allow user control of the excluded tags via prctl() Dave Martin (1): mm: Reserve asm-generic prot flags 0x10 and 0x20 for arch use Vincenzo Frascino (8): arm64: mte: system register definitions arm64: mte: CPU feature detection and initial sysreg configuration arm64: mte: Tags-aware clear_page() implementation arm64: mte: Tags-aware copy_page() implementation arm64: mte: Add specific SIGSEGV codes arm64: mte: Handle synchronous and asynchronous tag check faults arm64: mte: Kconfig entry arm64: mte: Add Memory Tagging Extension documentation Documentation/arm64/cpu-feature-registers.rst | 4 + Documentation/arm64/elf_hwcaps.rst | 4 + Documentation/arm64/index.rst | 1 + .../arm64/memory-tagging-extension.rst | 229 ++++++++++++++++++ arch/arm64/Kconfig | 32 +++ arch/arm64/include/asm/alternative.h | 8 +- arch/arm64/include/asm/assembler.h | 16 ++ arch/arm64/include/asm/cpucaps.h | 5 +- arch/arm64/include/asm/cpufeature.h | 6 + arch/arm64/include/asm/hwcap.h | 1 + arch/arm64/include/asm/kvm_arm.h | 3 +- arch/arm64/include/asm/memory.h | 17 +- arch/arm64/include/asm/mman.h | 78 ++++++ arch/arm64/include/asm/mte.h | 11 + arch/arm64/include/asm/page.h | 4 +- arch/arm64/include/asm/pgtable-prot.h | 2 + arch/arm64/include/asm/pgtable.h | 7 +- arch/arm64/include/asm/processor.h | 4 + arch/arm64/include/asm/sysreg.h | 70 ++++++ arch/arm64/include/asm/thread_info.h | 4 +- arch/arm64/include/uapi/asm/hwcap.h | 2 + arch/arm64/include/uapi/asm/mman.h | 14 ++ arch/arm64/include/uapi/asm/ptrace.h | 1 + arch/arm64/kernel/cpufeature.c | 59 +++++ arch/arm64/kernel/cpuinfo.c | 2 + arch/arm64/kernel/entry.S | 17 ++ arch/arm64/kernel/process.c | 141 ++++++++++- arch/arm64/kernel/ptrace.c | 2 +- arch/arm64/kernel/signal.c | 8 + arch/arm64/lib/Makefile | 2 + arch/arm64/lib/clear_page.S | 7 +- arch/arm64/lib/copy_page.S | 23 ++ arch/arm64/lib/mte.S | 46 ++++ arch/arm64/mm/Makefile | 1 + arch/arm64/mm/cmppages.c | 26 ++ arch/arm64/mm/dump.c | 4 + arch/arm64/mm/fault.c | 9 +- arch/arm64/mm/mmu.c | 22 +- arch/arm64/mm/proc.S | 31 ++- fs/proc/task_mmu.c | 3 + include/linux/mm.h | 8 + include/linux/mman.h | 20 +- include/uapi/asm-generic/mman-common.h | 2 + include/uapi/asm-generic/siginfo.h | 9 +- include/uapi/linux/prctl.h | 9 + mm/mmap.c | 9 + mm/mprotect.c | 8 + mm/shmem.c | 3 + mm/util.c | 2 +- scripts/Kconfig.include | 4 + 50 files changed, 958 insertions(+), 42 deletions(-) create mode 100644 Documentation/arm64/memory-tagging-extension.rst create mode 100644 arch/arm64/include/asm/mman.h create mode 100644 arch/arm64/include/asm/mte.h create mode 100644 arch/arm64/include/uapi/asm/mman.h create mode 100644 arch/arm64/lib/mte.S create mode 100644 arch/arm64/mm/cmppages.c