From 915b7f6f9a5e232c138bb36743a1fdb0fcf2c432 Mon Sep 17 00:00:00 2001 From: Gustavo Luiz Duarte Date: Tue, 11 Feb 2020 00:38:30 -0300 Subject: [PATCH] selftests/powerpc: Add tm-signal-pagefault test This test triggers a TM Bad Thing by raising a signal in transactional state and forcing a pagefault to happen in kernelspace when the kernel signal handling code first touches the user signal stack. This is inspired by the test tm-signal-context-force-tm but uses userfaultfd to make the test deterministic. While this test always triggers the bug in one run, I had to execute tm-signal-context-force-tm several times (the test runs 5000 times each execution) to trigger the same bug. tm-signal-context-force-tm is kept instead of replaced because, while this test is more reliable and triggers the same bug, tm-signal-context-force-tm has a better coverage, in the sense that by running the test several times it might trigger the pagefault and/or be preempted at different places. v3: skip test if userfaultfd is unavailable. Signed-off-by: Gustavo Luiz Duarte Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20200211033831.11165-2-gustavold@linux.ibm.com --- tools/testing/selftests/powerpc/tm/.gitignore | 1 + tools/testing/selftests/powerpc/tm/Makefile | 3 +- .../powerpc/tm/tm-signal-pagefault.c | 284 ++++++++++++++++++ 3 files changed, 287 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c diff --git a/tools/testing/selftests/powerpc/tm/.gitignore b/tools/testing/selftests/powerpc/tm/.gitignore index 98f2708d86cc..e1c72a4a3e91 100644 --- a/tools/testing/selftests/powerpc/tm/.gitignore +++ b/tools/testing/selftests/powerpc/tm/.gitignore @@ -13,6 +13,7 @@ tm-signal-context-chk-vmx tm-signal-context-chk-vsx tm-signal-context-force-tm tm-signal-sigreturn-nt +tm-signal-pagefault tm-vmx-unavail tm-unavailable tm-trap diff --git a/tools/testing/selftests/powerpc/tm/Makefile b/tools/testing/selftests/powerpc/tm/Makefile index b15a1a325bd0..b1d99736f8b8 100644 --- a/tools/testing/selftests/powerpc/tm/Makefile +++ b/tools/testing/selftests/powerpc/tm/Makefile @@ -5,7 +5,7 @@ SIGNAL_CONTEXT_CHK_TESTS := tm-signal-context-chk-gpr tm-signal-context-chk-fpu TEST_GEN_PROGS := tm-resched-dscr tm-syscall tm-signal-msr-resv tm-signal-stack \ tm-vmxcopy tm-fork tm-tar tm-tmspr tm-vmx-unavail tm-unavailable tm-trap \ $(SIGNAL_CONTEXT_CHK_TESTS) tm-sigreturn tm-signal-sigreturn-nt \ - tm-signal-context-force-tm tm-poison + tm-signal-context-force-tm tm-poison tm-signal-pagefault top_srcdir = ../../../../.. include ../../lib.mk @@ -22,6 +22,7 @@ $(OUTPUT)/tm-resched-dscr: ../pmu/lib.c $(OUTPUT)/tm-unavailable: CFLAGS += -O0 -pthread -m64 -Wno-error=uninitialized -mvsx $(OUTPUT)/tm-trap: CFLAGS += -O0 -pthread -m64 $(OUTPUT)/tm-signal-context-force-tm: CFLAGS += -pthread -m64 +$(OUTPUT)/tm-signal-pagefault: CFLAGS += -pthread -m64 SIGNAL_CONTEXT_CHK_TESTS := $(patsubst %,$(OUTPUT)/%,$(SIGNAL_CONTEXT_CHK_TESTS)) $(SIGNAL_CONTEXT_CHK_TESTS): tm-signal.S diff --git a/tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c b/tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c new file mode 100644 index 000000000000..5908bc6abe60 --- /dev/null +++ b/tools/testing/selftests/powerpc/tm/tm-signal-pagefault.c @@ -0,0 +1,284 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Copyright 2020, Gustavo Luiz Duarte, IBM Corp. + * + * This test starts a transaction and triggers a signal, forcing a pagefault to + * happen when the kernel signal handling code touches the user signal stack. + * + * In order to avoid pre-faulting the signal stack memory and to force the + * pagefault to happen precisely in the kernel signal handling code, the + * pagefault handling is done in userspace using the userfaultfd facility. + * + * Further pagefaults are triggered by crafting the signal handler's ucontext + * to point to additional memory regions managed by the userfaultfd, so using + * the same mechanism used to avoid pre-faulting the signal stack memory. + * + * On failure (bug is present) kernel crashes or never returns control back to + * userspace. If bug is not present, tests completes almost immediately. + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include "tm.h" + + +#define UF_MEM_SIZE 655360 /* 10 x 64k pages */ + +/* Memory handled by userfaultfd */ +static char *uf_mem; +static size_t uf_mem_offset = 0; + +/* + * Data that will be copied into the faulting pages (instead of zero-filled + * pages). This is used to make the test more reliable and avoid segfaulting + * when we return from the signal handler. Since we are making the signal + * handler's ucontext point to newly allocated memory, when that memory is + * paged-in it will contain the expected content. + */ +static char backing_mem[UF_MEM_SIZE]; + +static size_t pagesize; + +/* + * Return a chunk of at least 'size' bytes of memory that will be handled by + * userfaultfd. If 'backing_data' is not NULL, its content will be save to + * 'backing_mem' and then copied into the faulting pages when the page fault + * is handled. + */ +void *get_uf_mem(size_t size, void *backing_data) +{ + void *ret; + + if (uf_mem_offset + size > UF_MEM_SIZE) { + fprintf(stderr, "Requesting more uf_mem than expected!\n"); + exit(EXIT_FAILURE); + } + + ret = &uf_mem[uf_mem_offset]; + + /* Save the data that will be copied into the faulting page */ + if (backing_data != NULL) + memcpy(&backing_mem[uf_mem_offset], backing_data, size); + + /* Reserve the requested amount of uf_mem */ + uf_mem_offset += size; + /* Keep uf_mem_offset aligned to the page size (round up) */ + uf_mem_offset = (uf_mem_offset + pagesize - 1) & ~(pagesize - 1); + + return ret; +} + +void *fault_handler_thread(void *arg) +{ + struct uffd_msg msg; /* Data read from userfaultfd */ + long uffd; /* userfaultfd file descriptor */ + struct uffdio_copy uffdio_copy; + struct pollfd pollfd; + ssize_t nread, offset; + + uffd = (long) arg; + + for (;;) { + pollfd.fd = uffd; + pollfd.events = POLLIN; + if (poll(&pollfd, 1, -1) == -1) { + perror("poll() failed"); + exit(EXIT_FAILURE); + } + + nread = read(uffd, &msg, sizeof(msg)); + if (nread == 0) { + fprintf(stderr, "read(): EOF on userfaultfd\n"); + exit(EXIT_FAILURE); + } + + if (nread == -1) { + perror("read() failed"); + exit(EXIT_FAILURE); + } + + /* We expect only one kind of event */ + if (msg.event != UFFD_EVENT_PAGEFAULT) { + fprintf(stderr, "Unexpected event on userfaultfd\n"); + exit(EXIT_FAILURE); + } + + /* + * We need to handle page faults in units of pages(!). + * So, round faulting address down to page boundary. + */ + uffdio_copy.dst = msg.arg.pagefault.address & ~(pagesize-1); + + offset = (char *) uffdio_copy.dst - uf_mem; + uffdio_copy.src = (unsigned long) &backing_mem[offset]; + + uffdio_copy.len = pagesize; + uffdio_copy.mode = 0; + uffdio_copy.copy = 0; + if (ioctl(uffd, UFFDIO_COPY, &uffdio_copy) == -1) { + perror("ioctl-UFFDIO_COPY failed"); + exit(EXIT_FAILURE); + } + } +} + +void setup_uf_mem(void) +{ + long uffd; /* userfaultfd file descriptor */ + pthread_t thr; + struct uffdio_api uffdio_api; + struct uffdio_register uffdio_register; + int ret; + + pagesize = sysconf(_SC_PAGE_SIZE); + + /* Create and enable userfaultfd object */ + uffd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK); + if (uffd == -1) { + perror("userfaultfd() failed"); + exit(EXIT_FAILURE); + } + uffdio_api.api = UFFD_API; + uffdio_api.features = 0; + if (ioctl(uffd, UFFDIO_API, &uffdio_api) == -1) { + perror("ioctl-UFFDIO_API failed"); + exit(EXIT_FAILURE); + } + + /* + * Create a private anonymous mapping. The memory will be demand-zero + * paged, that is, not yet allocated. When we actually touch the memory + * the related page will be allocated via the userfaultfd mechanism. + */ + uf_mem = mmap(NULL, UF_MEM_SIZE, PROT_READ | PROT_WRITE, + MAP_PRIVATE | MAP_ANONYMOUS, -1, 0); + if (uf_mem == MAP_FAILED) { + perror("mmap() failed"); + exit(EXIT_FAILURE); + } + + /* + * Register the memory range of the mapping we've just mapped to be + * handled by the userfaultfd object. In 'mode' we request to track + * missing pages (i.e. pages that have not yet been faulted-in). + */ + uffdio_register.range.start = (unsigned long) uf_mem; + uffdio_register.range.len = UF_MEM_SIZE; + uffdio_register.mode = UFFDIO_REGISTER_MODE_MISSING; + if (ioctl(uffd, UFFDIO_REGISTER, &uffdio_register) == -1) { + perror("ioctl-UFFDIO_REGISTER"); + exit(EXIT_FAILURE); + } + + /* Create a thread that will process the userfaultfd events */ + ret = pthread_create(&thr, NULL, fault_handler_thread, (void *) uffd); + if (ret != 0) { + fprintf(stderr, "pthread_create(): Error. Returned %d\n", ret); + exit(EXIT_FAILURE); + } +} + +/* + * Assumption: the signal was delivered while userspace was in transactional or + * suspended state, i.e. uc->uc_link != NULL. + */ +void signal_handler(int signo, siginfo_t *si, void *uc) +{ + ucontext_t *ucp = uc; + + /* Skip 'trap' after returning, otherwise we get a SIGTRAP again */ + ucp->uc_link->uc_mcontext.regs->nip += 4; + + ucp->uc_mcontext.v_regs = + get_uf_mem(sizeof(elf_vrreg_t), ucp->uc_mcontext.v_regs); + + ucp->uc_link->uc_mcontext.v_regs = + get_uf_mem(sizeof(elf_vrreg_t), ucp->uc_link->uc_mcontext.v_regs); + + ucp->uc_link = get_uf_mem(sizeof(ucontext_t), ucp->uc_link); +} + +bool have_userfaultfd(void) +{ + long rc; + + errno = 0; + rc = syscall(__NR_userfaultfd, -1); + + return rc == 0 || errno != ENOSYS; +} + +int tm_signal_pagefault(void) +{ + struct sigaction sa; + stack_t ss; + + SKIP_IF(!have_htm()); + SKIP_IF(!have_userfaultfd()); + + setup_uf_mem(); + + /* + * Set an alternative stack that will generate a page fault when the + * signal is raised. The page fault will be treated via userfaultfd, + * i.e. via fault_handler_thread. + */ + ss.ss_sp = get_uf_mem(SIGSTKSZ, NULL); + ss.ss_size = SIGSTKSZ; + ss.ss_flags = 0; + if (sigaltstack(&ss, NULL) == -1) { + perror("sigaltstack() failed"); + exit(EXIT_FAILURE); + } + + sa.sa_flags = SA_SIGINFO | SA_ONSTACK; + sa.sa_sigaction = signal_handler; + if (sigaction(SIGTRAP, &sa, NULL) == -1) { + perror("sigaction() failed"); + exit(EXIT_FAILURE); + } + + /* Trigger a SIGTRAP in transactional state */ + asm __volatile__( + "tbegin.;" + "beq 1f;" + "trap;" + "1: ;" + : : : "memory"); + + /* Trigger a SIGTRAP in suspended state */ + asm __volatile__( + "tbegin.;" + "beq 1f;" + "tsuspend.;" + "trap;" + "tresume.;" + "1: ;" + : : : "memory"); + + return EXIT_SUCCESS; +} + +int main(int argc, char **argv) +{ + /* + * Depending on kernel config, the TM Bad Thing might not result in a + * crash, instead the kernel never returns control back to userspace, so + * set a tight timeout. If the test passes it completes almost + * immediately. + */ + test_harness_set_timeout(2); + return test_harness(tm_signal_pagefault, "tm_signal_pagefault"); +}