Date: Thu, 10 Jan 2019 14:09:32 -0700 From: Khalid Aziz <khalid.aziz@...cle.com> To: juergh@...il.com, tycho@...ho.ws, jsteckli@...zon.de, ak@...ux.intel.com, torvalds@...ux-foundation.org, liran.alon@...cle.com, keescook@...gle.com, konrad.wilk@...cle.com Cc: Khalid Aziz <khalid.aziz@...cle.com>, deepa.srinivasan@...cle.com, chris.hyser@...cle.com, tyhicks@...onical.com, dwmw@...zon.co.uk, andrew.cooper3@...rix.com, jcm@...hat.com, boris.ostrovsky@...cle.com, kanth.ghatraju@...cle.com, joao.m.martins@...cle.com, jmattson@...gle.com, pradeep.vincent@...cle.com, john.haxby@...cle.com, tglx@...utronix.de, kirill.shutemov@...ux.intel.com, hch@....de, steven.sistare@...cle.com, kernel-hardening@...ts.openwall.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org Subject: [RFC PATCH v7 00/16] Add support for eXclusive Page Frame Ownership I am continuing to build on the work Juerg, Tycho and Julian have done on XPFO. After the last round of updates, we were seeing very significant performance penalties when stale TLB entries were flushed actively after an XPFO TLB update. Benchmark for measuring performance is kernel build using parallel make. To get full protection from ret2dir attackes, we must flush stale TLB entries. Performance penalty from flushing stale TLB entries goes up as the number of cores goes up. On a desktop class machine with only 4 cores, enabling TLB flush for stale entries causes system time for "make -j4" to go up by a factor of 2.614x but on a larger machine with 96 cores, system time with "make -j60" goes up by a factor of 26.366x! I have been working on reducing this performance penalty. I implemented a solution to reduce performance penalty and that has had large impact. When XPFO code flushes stale TLB entries, it does so for all CPUs on the system which may include CPUs that may not have any matching TLB entries or may never be scheduled to run the userspace task causing TLB flush. Problem is made worse by the fact that if number of entries being flushed exceeds tlb_single_page_flush_ceiling, it results in a full TLB flush on every CPU. A rogue process can launch a ret2dir attack only from a CPU that has dual mapping for its pages in physmap in its TLB. We can hence defer TLB flush on a CPU until a process that would have caused a TLB flush is scheduled on that CPU. I have added a cpumask to task_struct which is then used to post pending TLB flush on CPUs other than the one a process is running on. This cpumask is checked when a process migrates to a new CPU and TLB is flushed at that time. I measured system time for parallel make with unmodified 4.20 kernel, 4.20 with XPFO patches before this optimization and then again after applying this optimization. Here are the results: Hardware: 96-core Intel Xeon Platinum 8160 CPU @ 2.10GHz, 768 GB RAM make -j60 all 4.20 915.183s 4.20+XPFO 24129.354s 26.366x 4.20+XPFO+Deferred flush 1216.987s 1.330xx Hardware: 4-core Intel Core i5-3550 CPU @ 3.30GHz, 8G RAM make -j4 all 4.20 607.671s 4.20+XPFO 1588.646s 2.614x 4.20+XPFO+Deferred flush 794.473s 1.307xx 30+% overhead is still very high and there is room for improvement. Dave Hansen had suggested batch updating TLB entries and Tycho had created an initial implementation but I have not been able to get that to work correctly. I am still working on it and I suspect we will see a noticeable improvement in performance with that. In the code I added, I post a pending full TLB flush to all other CPUs even when number of TLB entries being flushed on current CPU does not exceed tlb_single_page_flush_ceiling. There has to be a better way to do this. I just haven't found an efficient way to implemented delayed limited TLB flush on other CPUs. I am not entirely sure if switch_mm_irqs_off() is indeed the right place to perform the pending TLB flush for a CPU. Any feedback on that will be very helpful. Delaying full TLB flushes on other CPUs seems to help tremendously, so if there is a better way to implement the same thing than what I have done in patch 16, I am open to ideas. Performance with this patch set is good enough to use these as starting point for further refinement before we merge it into main kernel, hence RFC. Since not flushing stale TLB entries creates a false sense of security, I would recommend making TLB flush mandatory and eliminate the "xpfotlbflush" kernel parameter (patch "mm, x86: omit TLB flushing by default for XPFO page table modifications"). What remains to be done beyond this patch series: 1. Performance improvements 2. Remove xpfotlbflush parameter 3. Re-evaluate the patch "arm64/mm: Add support for XPFO to swiotlb" from Juerg. I dropped it for now since swiotlb code for ARM has changed a lot in 4.20. 4. Extend the patch "xpfo, mm: Defer TLB flushes for non-current CPUs" to other architectures besides x86. --------------------------------------------------------- Juerg Haefliger (5): mm, x86: Add support for eXclusive Page Frame Ownership (XPFO) swiotlb: Map the buffer if it was unmapped by XPFO arm64/mm: Add support for XPFO arm64/mm, xpfo: temporarily map dcache regions lkdtm: Add test for XPFO Julian Stecklina (4): mm, x86: omit TLB flushing by default for XPFO page table modifications xpfo, mm: remove dependency on CONFIG_PAGE_EXTENSION xpfo, mm: optimize spinlock usage in xpfo_kunmap EXPERIMENTAL: xpfo, mm: optimize spin lock usage in xpfo_kmap Khalid Aziz (2): xpfo, mm: Fix hang when booting with "xpfotlbflush" xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) Tycho Andersen (5): mm: add MAP_HUGETLB support to vm_mmap x86: always set IF before oopsing from page fault xpfo: add primitives for mapping underlying memory arm64/mm: disable section/contiguous mappings if XPFO is enabled mm: add a user_virt_to_phys symbol .../admin-guide/kernel-parameters.txt | 2 + arch/arm64/Kconfig | 1 + arch/arm64/mm/Makefile | 2 + arch/arm64/mm/flush.c | 7 + arch/arm64/mm/mmu.c | 2 +- arch/arm64/mm/xpfo.c | 58 ++++ arch/x86/Kconfig | 1 + arch/x86/include/asm/pgtable.h | 26 ++ arch/x86/include/asm/tlbflush.h | 1 + arch/x86/mm/Makefile | 2 + arch/x86/mm/fault.c | 10 + arch/x86/mm/pageattr.c | 23 +- arch/x86/mm/tlb.c | 27 ++ arch/x86/mm/xpfo.c | 171 ++++++++++++ drivers/misc/lkdtm/Makefile | 1 + drivers/misc/lkdtm/core.c | 3 + drivers/misc/lkdtm/lkdtm.h | 5 + drivers/misc/lkdtm/xpfo.c | 194 ++++++++++++++ include/linux/highmem.h | 15 +- include/linux/mm.h | 2 + include/linux/mm_types.h | 8 + include/linux/page-flags.h | 13 + include/linux/sched.h | 9 + include/linux/xpfo.h | 90 +++++++ include/trace/events/mmflags.h | 10 +- kernel/dma/swiotlb.c | 3 +- mm/Makefile | 1 + mm/mmap.c | 19 +- mm/page_alloc.c | 3 + mm/util.c | 32 +++ mm/xpfo.c | 247 ++++++++++++++++++ security/Kconfig | 29 ++ 32 files changed, 974 insertions(+), 43 deletions(-) create mode 100644 arch/arm64/mm/xpfo.c create mode 100644 arch/x86/mm/xpfo.c create mode 100644 drivers/misc/lkdtm/xpfo.c create mode 100644 include/linux/xpfo.h create mode 100644 mm/xpfo.c -- 2.17.1
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