This is another update to 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 2.61x but on a larger machine with 96 cores, system time with "make -j60" goes up by a factor of 26.37x! I have been working on reducing this performance penalty. I implemented two solutions to reduce performance penalty and that has had large impact. XPFO code flushes TLB every time a page is allocated to userspace. It does so by sending IPIs to all processors to flush TLB. Back to back allocations of pages to userspace on multiple processors results in a storm of IPIs. Each one of these incoming IPIs is handled by a processor by flushing its TLB. To reduce this IPI storm, I have added a per CPU flag that can be set to tell a processor to flush its TLB. A processor checks this flag on every context switch. If the flag is set, it flushes its TLB and clears the flag. This allows for multiple TLB flush requests to a single CPU to be combined into a single request. A kernel TLB entry for a page that has been allocated to userspace is flushed on all processors unlike the previous version of this patch. A processor could hold a stale kernel TLB entry that was removed on another processor until the next context switch. A local userspace page allocation by the currently running process could force the TLB flush earlier for such entries. The other solution reduces the number of TLB flushes required, by performing TLB flush for multiple pages at one time when pages are refilled on the per-cpu freelist. If the pages being addedd to per-cpu freelist are marked for userspace allocation, TLB entries for these pages can be flushed upfront and pages tagged as currently unmapped. When any such page is allocated to userspace, there is no need to performa a TLB flush at that time any more. This batching of TLB flushes reduces performance imapct further. Similarly when these user pages are freed by userspace and added back to per-cpu free list, they are left unmapped and tagged so. This further optimization reduced performance impact from 1.32x to 1.28x for 96-core server and from 1.31x to 1.27x for a 4-core desktop. I measured system time for parallel make with unmodified 4.20 kernel, 4.20 with XPFO patches before these patches and then again after applying each of these patches. Here are the results: Hardware: 96-core Intel Xeon Platinum 8160 CPU @ 2.10GHz, 768 GB RAM make -j60 all 5.0 913.862s 5.0+this patch series 1165.259ss 1.28x Hardware: 4-core Intel Core i5-3550 CPU @ 3.30GHz, 8G RAM make -j4 all 5.0 610.642s 5.0+this patch series 773.075s 1.27x 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. I have restructurerd the patches in this version to separate out architecture independent code. I folded much of the code improvement by Julian to not use page extension into patch 3. What remains to be done beyond this patch series: 1. Performance improvements: Ideas to explore - (1) kernel mappings private to an mm, (2) Any others?? 2. 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 since this patch was written. I could use help from ARM experts on this. 3. Extend the patch "xpfo, mm: Defer TLB flushes for non-current CPUs" to other architectures besides x86. 4. Change kmap to not map the page back to physmap, instead map it to a new va similar to what kmap_high does. Mapping page back into physmap re-opens the ret2dir security for the duration of kmap. All of the kmap_high and related code can be reused for this but that will require restructuring that code so it can be built for 64-bits as well. Any objections to that? --------------------------------------------------------- Juerg Haefliger (6): mm: Add support for eXclusive Page Frame Ownership (XPFO) xpfo, x86: Add support for XPFO for x86-64 lkdtm: Add test for XPFO arm64/mm: Add support for XPFO swiotlb: Map the buffer if it was unmapped by XPFO arm64/mm, xpfo: temporarily map dcache regions Julian Stecklina (1): xpfo, mm: optimize spinlock usage in xpfo_kunmap Khalid Aziz (2): xpfo, mm: Defer TLB flushes for non-current CPUs (x86 only) xpfo, mm: Optimize XPFO TLB flushes by batching them together Tycho Andersen (4): mm: add MAP_HUGETLB support to vm_mmap x86: always set IF before oopsing from page fault mm: add a user_virt_to_phys symbol xpfo: add primitives for mapping underlying memory .../admin-guide/kernel-parameters.txt | 6 + 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 | 66 ++++++ 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 | 6 + arch/x86/mm/pageattr.c | 32 +-- arch/x86/mm/tlb.c | 39 ++++ arch/x86/mm/xpfo.c | 185 +++++++++++++++++ drivers/misc/lkdtm/Makefile | 1 + drivers/misc/lkdtm/core.c | 3 + drivers/misc/lkdtm/lkdtm.h | 5 + drivers/misc/lkdtm/xpfo.c | 196 ++++++++++++++++++ include/linux/highmem.h | 34 +-- include/linux/mm.h | 2 + include/linux/mm_types.h | 8 + include/linux/page-flags.h | 23 +- include/linux/xpfo.h | 191 +++++++++++++++++ include/trace/events/mmflags.h | 10 +- kernel/dma/swiotlb.c | 3 +- mm/Makefile | 1 + mm/compaction.c | 2 +- mm/internal.h | 2 +- mm/mmap.c | 19 +- mm/page_alloc.c | 19 +- mm/page_isolation.c | 2 +- mm/util.c | 32 +++ mm/xpfo.c | 170 +++++++++++++++ security/Kconfig | 27 +++ 34 files changed, 1047 insertions(+), 79 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
