[RFC PATCH v1 28/28] kselftest/riscv: kselftest for user mode cfi

debug
2024-01-25T06:30:40Z

From: Deepak Gupta <debug@rivosinc.com>

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@rivosinc.com>
---
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 ++
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
--
2.43.0