Can you enable CONFIG_VMAP_STACK for aarch64 kernels once this lands in 4.14? I'd like to see any problems flagged early and often on this... Jon. -------- Forwarded Message -------- Subject: [PATCHv2 00/14] arm64: VMAP_STACK support Date: Tue, 15 Aug 2017 13:50:35 +0100 From: Mark Rutland <mark.rutland@xxxxxxx> To: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx CC: ard.biesheuvel@xxxxxxxxxx, catalin.marinas@xxxxxxx, james.morse@xxxxxxx, labbott@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, luto@xxxxxxxxxxxxxx, mark.rutland@xxxxxxx, matt@xxxxxxxxxxxxxxxxxxx, will.deacon@xxxxxxx, kernel-hardening@xxxxxxxxxxxxxxxxxx, keescook@xxxxxxxxxxxx Hi, Ard and I have worked together to implement vmap stack support for arm64. This supersedes our earlier vmap stack RFCs [0,1]. The git author stats are a little misleading, as I've teased parts out into smaller patches for review. The series is based on our stack dump rework [2,3], which can be found in the arm64/exception-stack branch [4] of my kernel.org repo. This series can be found in the arm64/vmap-stack branch [5] of the same repo. Since v1 [6]: * Fix typos * Update comments in entry assembly * Dump exception context (and stacks) before regs * Define safe adr_this_cpu for modules On arm64, there is no double-fault exception, as software saves exception context to the stack. An erroneous memory access taken during exception handling results in a data abort, as with any other erroneous memory access. To avoid taking these recursively, we must detect overflow by checking the SP before we attempt to store any context to the stack. Doing this efficiently requires a couple of tricks. For a naturally aligned stack, bits THREAD_SHIFT-1:0 of a valid SP may contain any arbitrary value: 0bXX .. 11111111111111 0bXX .. 11011001011100 0bXX .. 00000000000000 By aligning stacks to double their natural alignment, we know that the THREAD_SHIFT bit of any valid SP must be zero: 0bXX .. 0 11111111111111 0bXX .. 0 11011001011100 0bXX .. 0 00000000000000 ... while an overflow will result in this bit flipping, along with (some) other high-order bits: 0bXX .. 0 00000000000000 < SP -= 1 > 0bXX .. 1 11111111111111 ... and thus, we can detect overflows of up to THREAD_SIZE by testing the THREAD_SHIFT bit of the SP value. Provided we can get the SP into a general purpose register, we can perform this test with a single TBNZ instruction. We don't have scratch space to store a GPR, but we can (partially) swap the SP with a GPR using arithmetic to perform the test: add sp, sp, x0 // sp' = sp + x0 sub x0, sp, x0 // x0' = sp' - x0 = (sp + x0) - x0 = sp tbnz x0, #THREAD_SHIFT, overflow_handler sub x0, sp, x0 // sp' - x0' = (sp + x0) - sp = x0 sub sp, sp, x0 // sp' - x0 = (sp + x0) - x0 = sp This series implements this approach, along with the other requisite changes required to make this work. The SP test is performed for all exceptions, after compensating for the size of the exception registers, allowing the original exception context to be preserved in entirety. The tests themselves are folded into the exception vectors, minimizing their impact. To ensure that IRQ stack overflows are detected and handled, IRQ stacks are now dynamically allocated, with guard pages. I've given the series some light testing with LKDTM, Syzkaller, Vince Weaver's perf fuzzer, and a few combinations of debug options. I haven't compared performance of the entire series to a baseline kernel, but from testing so far the cost of the SP test falls in the noise for a kernel build workload on Cortex-A57. Many thanks to Ard for putting up with my meddling, and also to Laura, James, Catalin, and Will for comments and testing. Thanks, Mark. [0] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-July/518368.html [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-July/518434.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-July/520705.html [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-July/521435.html [4] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/exception-stack [5] git://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git arm64/vmap-stack [6] http://lists.infradead.org/pipermail/linux-arm-kernel/2017-August/524179.html Ard Biesheuvel (2): arm64: kernel: remove {THREAD,IRQ_STACK}_START_SP arm64: assembler: allow adr_this_cpu to use the stack pointer Mark Rutland (12): arm64: remove __die()'s stack dump fork: allow arch-override of VMAP stack alignment arm64: factor out PAGE_* and CONT_* definitions arm64: clean up THREAD_* definitions arm64: clean up irq stack definitions arm64: move SEGMENT_ALIGN to <asm/memory.h> efi/arm64: add EFI_KIMG_ALIGN arm64: factor out entry stack manipulation arm64: use an irq stack pointer arm64: add basic VMAP_STACK support arm64: add on_accessible_stack() arm64: add VMAP_STACK overflow detection arch/arm64/Kconfig | 1 + arch/arm64/include/asm/assembler.h | 8 +- arch/arm64/include/asm/efi.h | 8 ++ arch/arm64/include/asm/irq.h | 25 ------ arch/arm64/include/asm/memory.h | 53 +++++++++++++ arch/arm64/include/asm/page-def.h | 34 +++++++++ arch/arm64/include/asm/page.h | 12 +-- arch/arm64/include/asm/processor.h | 2 +- arch/arm64/include/asm/stacktrace.h | 60 ++++++++++++++- arch/arm64/include/asm/thread_info.h | 10 +-- arch/arm64/kernel/entry.S | 121 ++++++++++++++++++++++++------ arch/arm64/kernel/irq.c | 40 +++++++++- arch/arm64/kernel/ptrace.c | 1 + arch/arm64/kernel/smp.c | 2 +- arch/arm64/kernel/stacktrace.c | 7 +- arch/arm64/kernel/traps.c | 44 ++++++++++- arch/arm64/kernel/vmlinux.lds.S | 18 +---- drivers/firmware/efi/libstub/arm64-stub.c | 6 +- kernel/fork.c | 5 +- 19 files changed, 353 insertions(+), 104 deletions(-) create mode 100644 arch/arm64/include/asm/page-def.h -- 1.9.1 _______________________________________________ kernel mailing list -- kernel@xxxxxxxxxxxxxxxxxxxxxxx To unsubscribe send an email to kernel-leave@xxxxxxxxxxxxxxxxxxxxxxx
