On 3/29/24 9:44 AM, Deepak Gupta wrote:
> Adds kselftest for RISC-V control flow integrity implementation for user
> mode. There is not a lot going on in kernel for enabling landing pad for
> user mode. Thus kselftest simply enables landing pad for the binary and
> a signal handler is registered for SIGSEGV. Any control flow violation are
> reported as SIGSEGV with si_code = SEGV_CPERR. Test will fail on recieving
> any SEGV_CPERR. Shadow stack part has more changes in kernel and thus there
> are separate tests for that
> - enable and disable
> - Exercise `map_shadow_stack` syscall
> - `fork` test to make sure COW works for shadow stack pages
> - gup tests
> As of today kernel uses FOLL_FORCE when access happens to memory via
> /proc/<pid>/mem. Not breaking that for shadow stack
> - signal test. Make sure signal delivery results in token creation on
> shadow stack and consumes (and verifies) token on sigreturn
> - shadow stack protection test. attempts to write using regular store
> instruction on shadow stack memory must result in access faults
>
> Signed-off-by: Deepak Gupta <debug@xxxxxxxxxxxx>
> ---
> tools/testing/selftests/riscv/Makefile | 2 +-
> tools/testing/selftests/riscv/cfi/Makefile | 10 +
> .../testing/selftests/riscv/cfi/cfi_rv_test.h | 85 ++++
> .../selftests/riscv/cfi/riscv_cfi_test.c | 91 +++++
> .../testing/selftests/riscv/cfi/shadowstack.c | 376 ++++++++++++++++++
> .../testing/selftests/riscv/cfi/shadowstack.h | 39 ++
Please add generated binaries in the .gitignore files.
> 6 files changed, 602 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/riscv/cfi/Makefile
> create mode 100644 tools/testing/selftests/riscv/cfi/cfi_rv_test.h
> create mode 100644 tools/testing/selftests/riscv/cfi/riscv_cfi_test.c
> create mode 100644 tools/testing/selftests/riscv/cfi/shadowstack.c
> create mode 100644 tools/testing/selftests/riscv/cfi/shadowstack.h
>
> diff --git a/tools/testing/selftests/riscv/Makefile b/tools/testing/selftests/riscv/Makefile
> index 4a9ff515a3a0..867e5875b7ce 100644
> --- a/tools/testing/selftests/riscv/Makefile
> +++ b/tools/testing/selftests/riscv/Makefile
> @@ -5,7 +5,7 @@
> ARCH ?= $(shell uname -m 2>/dev/null || echo not)
>
> ifneq (,$(filter $(ARCH),riscv))
> -RISCV_SUBTARGETS ?= hwprobe vector mm
> +RISCV_SUBTARGETS ?= hwprobe vector mm cfi
> else
> RISCV_SUBTARGETS :=
> endif
> diff --git a/tools/testing/selftests/riscv/cfi/Makefile b/tools/testing/selftests/riscv/cfi/Makefile
> new file mode 100644
> index 000000000000..77f12157fa29
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/cfi/Makefile
> @@ -0,0 +1,10 @@
> +CFLAGS += -I$(top_srcdir)/tools/include
> +
> +CFLAGS += -march=rv64gc_zicfilp_zicfiss
> +
> +TEST_GEN_PROGS := cfitests
> +
> +include ../../lib.mk
> +
> +$(OUTPUT)/cfitests: riscv_cfi_test.c shadowstack.c
> + $(CC) -static -o$@ $(CFLAGS) $(LDFLAGS) $^
> diff --git a/tools/testing/selftests/riscv/cfi/cfi_rv_test.h b/tools/testing/selftests/riscv/cfi/cfi_rv_test.h
> new file mode 100644
> index 000000000000..27267a2e1008
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/cfi/cfi_rv_test.h
> @@ -0,0 +1,85 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef SELFTEST_RISCV_CFI_H
> +#define SELFTEST_RISCV_CFI_H
> +#include <stddef.h>
> +#include <sys/types.h>
> +#include "shadowstack.h"
> +
> +#define RISCV_CFI_SELFTEST_COUNT RISCV_SHADOW_STACK_TESTS
> +
> +#define CHILD_EXIT_CODE_SSWRITE 10
> +#define CHILD_EXIT_CODE_SIG_TEST 11
> +
> +#define BAD_POINTER (NULL)
> +
> +#define my_syscall5(num, arg1, arg2, arg3, arg4, arg5) \
> +({ \
> + register long _num __asm__ ("a7") = (num); \
> + register long _arg1 __asm__ ("a0") = (long)(arg1); \
> + register long _arg2 __asm__ ("a1") = (long)(arg2); \
> + register long _arg3 __asm__ ("a2") = (long)(arg3); \
> + register long _arg4 __asm__ ("a3") = (long)(arg4); \
> + register long _arg5 __asm__ ("a4") = (long)(arg5); \
> + \
> + __asm__ volatile ( \
> + "ecall\n" \
> + : "+r"(_arg1) \
> + : "r"(_arg2), "r"(_arg3), "r"(_arg4), "r"(_arg5), \
> + "r"(_num) \
> + : "memory", "cc" \
> + ); \
> + _arg1; \
> +})
> +
> +#define my_syscall3(num, arg1, arg2, arg3) \
> +({ \
> + register long _num __asm__ ("a7") = (num); \
> + register long _arg1 __asm__ ("a0") = (long)(arg1); \
> + register long _arg2 __asm__ ("a1") = (long)(arg2); \
> + register long _arg3 __asm__ ("a2") = (long)(arg3); \
> + \
> + __asm__ volatile ( \
> + "ecall\n" \
> + : "+r"(_arg1) \
> + : "r"(_arg2), "r"(_arg3), \
> + "r"(_num) \
> + : "memory", "cc" \
> + ); \
> + _arg1; \
> +})
> +
> +#ifndef __NR_prctl
> +#define __NR_prctl 167
> +#endif
> +
> +#ifndef __NR_map_shadow_stack
> +#define __NR_map_shadow_stack 453
> +#endif
> +
> +#define CSR_SSP 0x011
> +
> +#ifdef __ASSEMBLY__
> +#define __ASM_STR(x) x
> +#else
> +#define __ASM_STR(x) #x
> +#endif
> +
> +#define csr_read(csr) \
> +({ \
> + register unsigned long __v; \
> + __asm__ __volatile__ ("csrr %0, " __ASM_STR(csr) \
> + : "=r" (__v) : \
> + : "memory"); \
> + __v; \
> +})
> +
> +#define csr_write(csr, val) \
> +({ \
> + unsigned long __v = (unsigned long) (val); \
> + __asm__ __volatile__ ("csrw " __ASM_STR(csr) ", %0" \
> + : : "rK" (__v) \
> + : "memory"); \
> +})
> +
> +#endif
> diff --git a/tools/testing/selftests/riscv/cfi/riscv_cfi_test.c b/tools/testing/selftests/riscv/cfi/riscv_cfi_test.c
> new file mode 100644
> index 000000000000..c116ae4bb358
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/cfi/riscv_cfi_test.c
> @@ -0,0 +1,91 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include "../../kselftest.h"
> +#include <signal.h>
> +#include <asm/ucontext.h>
> +#include <linux/prctl.h>
> +#include "cfi_rv_test.h"
> +
> +/* do not optimize cfi related test functions */
> +#pragma GCC push_options
> +#pragma GCC optimize("O0")
> +
> +#define SEGV_CPERR 10 /* control protection fault */
> +
> +void sigsegv_handler(int signum, siginfo_t *si, void *uc)
> +{
> + struct ucontext *ctx = (struct ucontext *) uc;
> +
> + if (si->si_code == SEGV_CPERR) {
> + printf("Control flow violation happened somewhere\n");
> + printf("pc where violation happened %lx\n", ctx->uc_mcontext.gregs[0]);
> + exit(-1);
> + }
> +
> + /* null pointer deref */
> + if (si->si_addr == BAD_POINTER)
> + exit(CHILD_EXIT_CODE_NULL_PTR_DEREF);
> +
> + /* shadow stack write case */
> + exit(CHILD_EXIT_CODE_SSWRITE);
> +}
> +
> +int lpad_enable(void)
> +{
> + int ret = 0;
> +
> + ret = my_syscall5(__NR_prctl, PR_SET_INDIR_BR_LP_STATUS, PR_INDIR_BR_LP_ENABLE, 0, 0, 0);
> +
> + return ret;
> +}
> +
> +bool register_signal_handler(void)
> +{
> + struct sigaction sa = {};
> +
> + sa.sa_sigaction = sigsegv_handler;
> + sa.sa_flags = SA_SIGINFO;
> + if (sigaction(SIGSEGV, &sa, NULL)) {
> + printf("registering signal handler for landing pad violation failed\n");
> + return false;
> + }
> +
> + return true;
> +}
> +
> +int main(int argc, char *argv[])
> +{
> + int ret = 0;
> + unsigned long lpad_status = 0;
> +
> + ksft_print_header();
> +
> + ksft_set_plan(RISCV_CFI_SELFTEST_COUNT);
> +
> + ksft_print_msg("starting risc-v tests\n");
> +
> + /*
> + * Landing pad test. Not a lot of kernel changes to support landing
> + * pad for user mode except lighting up a bit in senvcfg via a prctl
> + * Enable landing pad through out the execution of test binary
> + */
> + ret = my_syscall5(__NR_prctl, PR_GET_INDIR_BR_LP_STATUS, &lpad_status, 0, 0, 0);
> + if (ret)
> + ksft_exit_skip("Get landing pad status failed with %d\n", ret);
> +
> + ret = lpad_enable();
> +
> + if (ret)
> + ksft_exit_skip("Enabling landing pad failed with %d\n", ret);
> +
> + if (!register_signal_handler())
> + ksft_exit_skip("registering signal handler for SIGSEGV failed\n");
> +
> + ksft_print_msg("landing pad enabled for binary\n");
> + ksft_print_msg("starting risc-v shadow stack tests\n");
> + execute_shadow_stack_tests();
> +
> + ksft_finished();
> +}
> +
> +#pragma GCC pop_options
> diff --git a/tools/testing/selftests/riscv/cfi/shadowstack.c b/tools/testing/selftests/riscv/cfi/shadowstack.c
> new file mode 100644
> index 000000000000..126654801bed
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/cfi/shadowstack.c
> @@ -0,0 +1,376 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +
> +#include "../../kselftest.h"
> +#include <sys/wait.h>
> +#include <signal.h>
> +#include <fcntl.h>
> +#include <unistd.h>
> +#include <sys/mman.h>
> +#include "shadowstack.h"
> +#include "cfi_rv_test.h"
> +
> +/* do not optimize shadow stack related test functions */
> +#pragma GCC push_options
> +#pragma GCC optimize("O0")
> +
> +void zar(void)
> +{
> + unsigned long ssp = 0, swaped_val = 0;
> +
> + ssp = csr_read(CSR_SSP);
> + printf("inside %s and shadow stack ptr is %lx\n", __func__, ssp);
> +}
> +
> +void bar(void)
> +{
> + printf("inside %s\n", __func__);
> + zar();
> +}
> +
> +void foo(void)
> +{
> + printf("inside %s\n", __func__);
> + bar();
> +}
> +
> +void zar_child(void)
> +{
> + unsigned long ssp = 0;
> +
> + ssp = csr_read(CSR_SSP);
> + printf("inside %s and shadow stack ptr is %lx\n", __func__, ssp);
> +}
> +
> +void bar_child(void)
> +{
> + printf("inside %s\n", __func__);
> + zar_child();
> +}
> +
> +void foo_child(void)
> +{
> + printf("inside %s\n", __func__);
> + bar_child();
> +}
> +
> +typedef void (call_func_ptr)(void);
> +/*
> + * call couple of functions to test push pop.
> + */
> +int shadow_stack_call_tests(call_func_ptr fn_ptr, bool parent)
> +{
> + if (parent)
> + printf("call test for parent\n");
> + else
> + printf("call test for child\n");
> +
> + (fn_ptr)();
> +
> + return 0;
> +}
> +
> +bool enable_disable_check(unsigned long test_num, void *ctx)
> +{
> + int ret = 0;
> +
> + if (!my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, PR_SHADOW_STACK_ENABLE, 0, 0, 0)) {
> + printf("Shadow stack was enabled\n");
> + shadow_stack_call_tests(&foo, true);
> +
> + ret = my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0, 0, 0, 0);
> + if (ret)
> + ksft_test_result_fail("shadow stack disable failed\n");
> + } else {
> + ksft_test_result_fail("shadow stack enable failed\n");
> + ret = -EINVAL;
> + }
> +
> + return ret ? false : true;
> +}
> +
> +/* forks a thread, and ensure shadow stacks fork out */
> +bool shadow_stack_fork_test(unsigned long test_num, void *ctx)
> +{
> + int pid = 0, child_status = 0, parent_pid = 0;
> +
> + printf("exercising shadow stack fork test\n");
> +
> + if (my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, PR_SHADOW_STACK_ENABLE, 0, 0, 0)) {
> + printf("shadow stack enable prctl failed\n");
> + return false;
> + }
> +
> + parent_pid = getpid();
> + pid = fork();
> +
> + if (pid) {
> + printf("Parent pid %d and child pid %d\n", parent_pid, pid);
> + shadow_stack_call_tests(&foo, true);
> + } else
> + shadow_stack_call_tests(&foo_child, false);
> +
> + if (pid) {
> + printf("waiting on child to finish\n");
> + wait(&child_status);
> + } else {
> + /* exit child gracefully */
> + exit(0);
> + }
> +
> + if (pid && WIFSIGNALED(child_status)) {
> + printf("child faulted");
> + return false;
> + }
> +
> + /* disable shadow stack again */
> + if (my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0, 0, 0, 0)) {
> + printf("shadow stack disable prctl failed\n");
> + return false;
> + }
> +
> + return true;
> +}
> +
> +/* exercise `map_shadow_stack`, pivot to it and call some functions to ensure it works */
> +#define SHADOW_STACK_ALLOC_SIZE 4096
> +bool shadow_stack_map_test(unsigned long test_num, void *ctx)
> +{
> + unsigned long shdw_addr;
> + int ret = 0;
> +
> + shdw_addr = my_syscall3(__NR_map_shadow_stack, NULL, SHADOW_STACK_ALLOC_SIZE, 0);
> +
> + if (((long) shdw_addr) <= 0) {
> + printf("map_shadow_stack failed with error code %d\n", (int) shdw_addr);
> + return false;
> + }
> +
> + ret = munmap((void *) shdw_addr, SHADOW_STACK_ALLOC_SIZE);
> +
> + if (ret) {
> + printf("munmap failed with error code %d\n", ret);
> + return false;
> + }
> +
> + return true;
> +}
> +
> +/*
> + * shadow stack protection tests. map a shadow stack and
> + * validate all memory protections work on it
> + */
> +bool shadow_stack_protection_test(unsigned long test_num, void *ctx)
> +{
> + unsigned long shdw_addr;
> + unsigned long *write_addr = NULL;
> + int ret = 0, pid = 0, child_status = 0;
> +
> + shdw_addr = my_syscall3(__NR_map_shadow_stack, NULL, SHADOW_STACK_ALLOC_SIZE, 0);
> +
> + if (((long) shdw_addr) <= 0) {
> + printf("map_shadow_stack failed with error code %d\n", (int) shdw_addr);
> + return false;
> + }
> +
> + write_addr = (unsigned long *) shdw_addr;
> + pid = fork();
> +
> + /* no child was created, return false */
> + if (pid == -1)
> + return false;
> +
> + /*
> + * try to perform a store from child on shadow stack memory
> + * it should result in SIGSEGV
> + */
> + if (!pid) {
> + /* below write must lead to SIGSEGV */
> + *write_addr = 0xdeadbeef;
> + } else {
> + wait(&child_status);
> + }
> +
> + /* test fail, if 0xdeadbeef present on shadow stack address */
> + if (*write_addr == 0xdeadbeef) {
> + printf("write suceeded\n");
> + return false;
> + }
> +
> + /* if child reached here, then fail */
> + if (!pid) {
> + printf("child reached unreachable state\n");
> + return false;
> + }
> +
> + /* if child exited via signal handler but not for write on ss */
> + if (WIFEXITED(child_status) &&
> + WEXITSTATUS(child_status) != CHILD_EXIT_CODE_SSWRITE) {
> + printf("child wasn't signaled for write on shadow stack\n");
> + return false;
> + }
> +
> + ret = munmap(write_addr, SHADOW_STACK_ALLOC_SIZE);
> + if (ret) {
> + printf("munmap failed with error code %d\n", ret);
> + return false;
> + }
> +
> + return true;
> +}
> +
> +#define SS_MAGIC_WRITE_VAL 0xbeefdead
> +
> +int gup_tests(int mem_fd, unsigned long *shdw_addr)
> +{
> + unsigned long val = 0;
> +
> + lseek(mem_fd, (unsigned long)shdw_addr, SEEK_SET);
> + if (read(mem_fd, &val, sizeof(val)) < 0) {
> + printf("reading shadow stack mem via gup failed\n");
> + return 1;
> + }
> +
> + val = SS_MAGIC_WRITE_VAL;
> + lseek(mem_fd, (unsigned long)shdw_addr, SEEK_SET);
> + if (write(mem_fd, &val, sizeof(val)) < 0) {
> + printf("writing shadow stack mem via gup failed\n");
> + return 1;
> + }
> +
> + if (*shdw_addr != SS_MAGIC_WRITE_VAL) {
> + printf("GUP write to shadow stack memory didn't happen\n");
> + return 1;
> + }
> +
> + return 0;
> +}
> +
> +bool shadow_stack_gup_tests(unsigned long test_num, void *ctx)
> +{
> + unsigned long shdw_addr = 0;
> + unsigned long *write_addr = NULL;
> + int fd = 0;
> + bool ret = false;
> +
> + shdw_addr = my_syscall3(__NR_map_shadow_stack, NULL, SHADOW_STACK_ALLOC_SIZE, 0);
> +
> + if (((long) shdw_addr) <= 0) {
> + printf("map_shadow_stack failed with error code %d\n", (int) shdw_addr);
> + return false;
> + }
> +
> + write_addr = (unsigned long *) shdw_addr;
> +
> + fd = open("/proc/self/mem", O_RDWR);
> + if (fd == -1)
> + return false;
> +
> + if (gup_tests(fd, write_addr)) {
> + printf("gup tests failed\n");
> + goto out;
> + }
> +
> + ret = true;
> +out:
> + if (shdw_addr && munmap(write_addr, SHADOW_STACK_ALLOC_SIZE)) {
> + printf("munmap failed with error code %d\n", ret);
> + ret = false;
> + }
> +
> + return ret;
> +}
> +
> +volatile bool break_loop;
> +
> +void sigusr1_handler(int signo)
> +{
> + printf("In sigusr1 handler\n");
> + break_loop = true;
> +}
> +
> +bool sigusr1_signal_test(void)
> +{
> + if (signal(SIGUSR1, sigusr1_handler) == SIG_ERR) {
> + printf("registerting sigusr1 handler failed\n");
> + return false;
> + }
> +
> + return true;
> +}
> +/*
> + * shadow stack signal test. shadow stack must be enabled.
> + * register a signal, fork another thread which is waiting
> + * on signal. Send a signal from parent to child, verify
> + * that signal was received by child. If not test fails
> + */
> +bool shadow_stack_signal_test(unsigned long test_num, void *ctx)
> +{
> + int pid = 0, child_status = 0;
> + unsigned long ssp = 0;
> +
> + if (my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, PR_SHADOW_STACK_ENABLE, 0, 0, 0)) {
> + printf("shadow stack enable prctl failed\n");
> + return false;
> + }
> +
> + pid = fork();
> +
> + if (pid == -1) {
> + printf("signal test: fork failed\n");
> + goto out;
> + }
> +
> + if (pid == 0) {
> + /* this should be caught by signal handler and do an exit */
> + if (!sigusr1_signal_test()) {
> + printf("sigusr1_signal_test failed\n");
> + exit(-1);
> + }
> +
> + while (!break_loop)
> + sleep(1);
> +
> + exit(11);
> + /* child shouldn't go beyond here */
> + }
> + /* send SIGUSR1 to child */
> + kill(pid, SIGUSR1);
> + wait(&child_status);
> +
> +out:
> + if (my_syscall5(__NR_prctl, PR_SET_SHADOW_STACK_STATUS, 0, 0, 0, 0)) {
> + printf("shadow stack disable prctl failed\n");
> + return false;
> + }
> +
> + return (WIFEXITED(child_status) &&
> + WEXITSTATUS(child_status) == 11);
> +}
> +
> +int execute_shadow_stack_tests(void)
> +{
> + int ret = 0;
> + unsigned long test_count = 0;
> + unsigned long shstk_status = 0;
> +
> + printf("Executing RISC-V shadow stack self tests\n");
> +
> + ret = my_syscall5(__NR_prctl, PR_GET_SHADOW_STACK_STATUS, &shstk_status, 0, 0, 0);
> +
> + if (ret != 0)
> + ksft_exit_skip("Get shadow stack status failed with %d\n", ret);
> +
> + /*
> + * If we are here that means get shadow stack status succeeded and
> + * thus shadow stack support is baked in the kernel.
> + */
> + while (test_count < ARRAY_SIZE(shstk_tests)) {
> + ksft_test_result((*shstk_tests[test_count].t_func)(test_count, NULL),
> + shstk_tests[test_count].name);
> + test_count++;
> + }
> +
> + return 0;
> +}
> +
> +#pragma GCC pop_options
> diff --git a/tools/testing/selftests/riscv/cfi/shadowstack.h b/tools/testing/selftests/riscv/cfi/shadowstack.h
> new file mode 100644
> index 000000000000..92cb0752238d
> --- /dev/null
> +++ b/tools/testing/selftests/riscv/cfi/shadowstack.h
> @@ -0,0 +1,39 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +
> +#ifndef SELFTEST_SHADOWSTACK_TEST_H
> +#define SELFTEST_SHADOWSTACK_TEST_H
> +#include <stddef.h>
> +#include <linux/prctl.h>
> +
> +/*
> + * a cfi test returns true for success or false for fail
> + * takes a number for test number to index into array and void pointer.
> + */
> +typedef bool (*shstk_test_func)(unsigned long test_num, void *);
> +
> +struct shadow_stack_tests {
> + char *name;
> + shstk_test_func t_func;
> +};
> +
> +bool enable_disable_check(unsigned long test_num, void *ctx);
> +bool shadow_stack_fork_test(unsigned long test_num, void *ctx);
> +bool shadow_stack_map_test(unsigned long test_num, void *ctx);
> +bool shadow_stack_protection_test(unsigned long test_num, void *ctx);
> +bool shadow_stack_gup_tests(unsigned long test_num, void *ctx);
> +bool shadow_stack_signal_test(unsigned long test_num, void *ctx);
> +
> +static struct shadow_stack_tests shstk_tests[] = {
> + { "enable disable\n", enable_disable_check },
> + { "shstk fork test\n", shadow_stack_fork_test },
> + { "map shadow stack syscall\n", shadow_stack_map_test },
> + { "shadow stack gup tests\n", shadow_stack_gup_tests },
> + { "shadow stack signal tests\n", shadow_stack_signal_test},
> + { "memory protections of shadow stack memory\n", shadow_stack_protection_test }
> +};
> +
> +#define RISCV_SHADOW_STACK_TESTS ARRAY_SIZE(shstk_tests)
> +
> +int execute_shadow_stack_tests(void);
> +
> +#endif
--
BR,
Muhammad Usama Anjum
