Date: Tue, 28 May 2024 14:52:09 +0000
From: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
To: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC: "x86@...nel.org" <x86@...nel.org>,
        "dave.hansen@...ux.intel.com"
	<dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo
 Molnar <mingo@...nel.org>,
        Keith Lucas <keith.lucas@...cle.com>
Subject: Re: [PATCH  v4 5/5] selftests/mm: Add new testcases for pkeys


> On May 28, 2024, at 7:43 AM, Aruna Ramakrishna <aruna.ramakrishna@...cle.com> wrote:
> 
> From: Keith Lucas <keith.lucas@...cle.com>
> 
> This commit adds a few new tests to exercise the signal handler flow,
> especially with pkey 0 disabled.
> 

Oops, I missed this “this commit”. I will rephrase the commit description.

Thanks,
Aruna
 
> [ Aruna: Adapted to upstream ]
> 
> Signed-off-by: Keith Lucas <keith.lucas@...cle.com>
> Signed-off-by: Aruna Ramakrishna <aruna.ramakrishna@...cle.com>
> ---
> tools/testing/selftests/mm/Makefile           |   5 +-
> tools/testing/selftests/mm/pkey-helpers.h     |  11 +-
> .../selftests/mm/pkey_sighandler_tests.c      | 480 ++++++++++++++++++
> tools/testing/selftests/mm/protection_keys.c  |  10 -
> 4 files changed, 494 insertions(+), 12 deletions(-)
> create mode 100644 tools/testing/selftests/mm/pkey_sighandler_tests.c
> 
> diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
> index 410495e0a611..1bb95960d28b 100644
> --- a/tools/testing/selftests/mm/Makefile
> +++ b/tools/testing/selftests/mm/Makefile
> @@ -2,6 +2,7 @@
> # Makefile for mm selftests
> 
> LOCAL_HDRS += $(selfdir)/mm/local_config.h $(top_srcdir)/mm/gup_test.h
> +LINUX_TOOL_INCLUDE = $(top_srcdir)/tools/include
> 
> include local_config.mk
> 
> @@ -32,7 +33,7 @@ endif
> # LDLIBS.
> MAKEFLAGS += --no-builtin-rules
> 
> -CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) $(KHDR_INCLUDES)
> +CFLAGS = -Wall -I $(top_srcdir) $(EXTRA_CFLAGS) -I$(LINUX_TOOL_INCLUDE) $(KHDR_INCLUDES)
> LDLIBS = -lrt -lpthread -lm
> 
> TEST_GEN_FILES = cow
> @@ -82,6 +83,7 @@ CAN_BUILD_X86_64 := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_64bit_pr
> CAN_BUILD_WITH_NOPIE := $(shell ./../x86/check_cc.sh "$(CC)" ../x86/trivial_program.c -no-pie)
> 
> VMTARGETS := protection_keys
> +VMTARGETS := pkey_sighandler_tests
> BINARIES_32 := $(VMTARGETS:%=%_32)
> BINARIES_64 := $(VMTARGETS:%=%_64)
> 
> @@ -100,6 +102,7 @@ else
> 
> ifneq (,$(findstring $(ARCH),powerpc))
> TEST_GEN_FILES += protection_keys
> +TEST_GEN_FILES += pkey_sighandler_tests
> endif
> 
> endif
> diff --git a/tools/testing/selftests/mm/pkey-helpers.h b/tools/testing/selftests/mm/pkey-helpers.h
> index 1af3156a9db8..2b1189c27167 100644
> --- a/tools/testing/selftests/mm/pkey-helpers.h
> +++ b/tools/testing/selftests/mm/pkey-helpers.h
> @@ -12,6 +12,7 @@
> #include <stdlib.h>
> #include <ucontext.h>
> #include <sys/mman.h>
> +#include <linux/compiler.h>
> 
> #include "../kselftest.h"
> 
> @@ -79,7 +80,15 @@ extern void abort_hooks(void);
> } \
> } while (0)
> 
> -__attribute__((noinline)) int read_ptr(int *ptr);
> +noinline int read_ptr(int *ptr)
> +{
> + /*
> + * Keep GCC from optimizing this away somehow
> + */
> + barrier();
> + return *ptr;
> +}
> +
> void expected_pkey_fault(int pkey);
> int sys_pkey_alloc(unsigned long flags, unsigned long init_val);
> int sys_pkey_free(unsigned long pkey);
> diff --git a/tools/testing/selftests/mm/pkey_sighandler_tests.c b/tools/testing/selftests/mm/pkey_sighandler_tests.c
> new file mode 100644
> index 000000000000..8a8dc284b40d
> --- /dev/null
> +++ b/tools/testing/selftests/mm/pkey_sighandler_tests.c
> @@ -0,0 +1,480 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Tests Memory Protection Keys (see Documentation/core-api/protection-keys.rst)
> + *
> + * The testcases in this file exercise various flows related to signal handling,
> + * using an alternate signal stack, with the default pkey (pkey 0) disabled.
> + *
> + * Compile with:
> + * gcc -mxsave      -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
> + * gcc -mxsave -m32 -o pkey_sighandler_tests -O2 -g -std=gnu99 -pthread -Wall pkey_sighandler_tests.c -I../../../../tools/include -lrt -ldl -lm
> + */
> +#define _GNU_SOURCE
> +#define __SANE_USERSPACE_TYPES__
> +#include <errno.h>
> +#include <sys/syscall.h>
> +#include <string.h>
> +#include <stdio.h>
> +#include <stdint.h>
> +#include <stdbool.h>
> +#include <signal.h>
> +#include <assert.h>
> +#include <stdlib.h>
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <unistd.h>
> +#include <pthread.h>
> +#include <limits.h>
> +
> +#include "pkey-helpers.h"
> +
> +#define STACK_SIZE PTHREAD_STACK_MIN
> +
> +void expected_pkey_fault(int pkey) {}
> +
> +pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
> +pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
> +siginfo_t siginfo = {0};
> +
> +/*
> + * We need to use inline assembly instead of glibc's syscall because glibc's
> + * syscall will attempt to access the PLT in order to call a library function
> + * which is protected by MPK 0 which we don't have access to.
> + */
> +static inline __always_inline
> +long syscall_raw(long n, long a1, long a2, long a3, long a4, long a5, long a6)
> +{
> + unsigned long ret;
> +#ifdef __x86_64__
> + register long r10 asm("r10") = a4;
> + register long r8 asm("r8") = a5;
> + register long r9 asm("r9") = a6;
> + asm volatile ("syscall"
> +      : "=a"(ret)
> +      : "a"(n), "D"(a1), "S"(a2), "d"(a3), "r"(r10), "r"(r8), "r"(r9)
> +      : "rcx", "r11", "memory");
> +#elif defined __i386__
> + asm volatile ("int $0x80"
> +      : "=a"(ret)
> +      : "a"(n), "b"(a1), "c"(a2), "d"(a3), "S"(a4), "D"(a5)
> +      : "memory");
> +#endif
> + return ret;
> +}
> +
> +static void sigsegv_handler(int signo, siginfo_t *info, void *ucontext)
> +{
> + pthread_mutex_lock(&mutex);
> +
> + memcpy(&siginfo, info, sizeof(siginfo_t));
> +
> + pthread_cond_signal(&cond);
> + pthread_mutex_unlock(&mutex);
> +
> + syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
> +}
> +
> +static void sigusr1_handler(int signo, siginfo_t *info, void *ucontext)
> +{
> + pthread_mutex_lock(&mutex);
> +
> + memcpy(&siginfo, info, sizeof(siginfo_t));
> +
> + pthread_cond_signal(&cond);
> + pthread_mutex_unlock(&mutex);
> +}
> +
> +static void sigusr2_handler(int signo, siginfo_t *info, void *ucontext)
> +{
> + /*
> + * pkru should be the init_pkru value which enabled MPK 0 so
> + * we can use library functions.
> + */
> + printf("%s invoked.\n", __func__);
> +}
> +
> +static void raise_sigusr2(void)
> +{
> + pid_t tid = 0;
> +
> + tid = syscall_raw(SYS_gettid, 0, 0, 0, 0, 0, 0);
> +
> + syscall_raw(SYS_tkill, tid, SIGUSR2, 0, 0, 0, 0);
> +
> + /*
> + * We should return from the signal handler here and be able to
> + * return to the interrupted thread.
> + */
> +}
> +
> +static void *thread_segv_with_pkey0_disabled(void *ptr)
> +{
> + /* Disable MPK 0 (and all others too) */
> + __write_pkey_reg(0x55555555);
> +
> + /* Segfault (with SEGV_MAPERR) */
> + *(int *) (0x1) = 1;
> + return NULL;
> +}
> +
> +static void *thread_segv_pkuerr_stack(void *ptr)
> +{
> + /* Disable MPK 0 (and all others too) */
> + __write_pkey_reg(0x55555555);
> +
> + /* After we disable MPK 0, we can't access the stack to return */
> + return NULL;
> +}
> +
> +static void *thread_segv_maperr_ptr(void *ptr)
> +{
> + stack_t *stack = ptr;
> + int *bad = (int *)1;
> +
> + /*
> + * Setup alternate signal stack, which should be pkey_mprotect()ed by
> + * MPK 0. The thread's stack cannot be used for signals because it is
> + * not accessible by the default init_pkru value of 0x55555554.
> + */
> + syscall_raw(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
> +
> + /* Disable MPK 0.  Only MPK 1 is enabled. */
> + __write_pkey_reg(0x55555551);
> +
> + /* Segfault */
> + *bad = 1;
> + syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
> + return NULL;
> +}
> +
> +/*
> + * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
> + * Note that the new thread stack and the alternate signal stack is
> + * protected by MPK 0.
> + */
> +static void test_sigsegv_handler_with_pkey0_disabled(void)
> +{
> + struct sigaction sa;
> + pthread_attr_t attr;
> + pthread_t thr;
> +
> + sa.sa_flags = SA_SIGINFO;
> +
> + sa.sa_sigaction = sigsegv_handler;
> + sigemptyset(&sa.sa_mask);
> + if (sigaction(SIGSEGV, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + memset(&siginfo, 0, sizeof(siginfo));
> +
> + pthread_attr_init(&attr);
> + pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> +
> + pthread_create(&thr, &attr, thread_segv_with_pkey0_disabled, NULL);
> +
> + pthread_mutex_lock(&mutex);
> + while (siginfo.si_signo == 0)
> + pthread_cond_wait(&cond, &mutex);
> + pthread_mutex_unlock(&mutex);
> +
> + ksft_test_result(siginfo.si_signo == SIGSEGV &&
> + siginfo.si_code == SEGV_MAPERR &&
> + siginfo.si_addr == (void *)1,
> + "%s\n", __func__);
> +}
> +
> +/*
> + * Verify that the sigsegv handler is invoked when pkey 0 is disabled.
> + * Note that the new thread stack and the alternate signal stack is
> + * protected by MPK 0, which renders them inaccessible when MPK 0
> + * is disabled. So just the return from the thread should cause a
> + * segfault with SEGV_PKUERR.
> + */
> +static void test_sigsegv_handler_cannot_access_stack(void)
> +{
> + struct sigaction sa;
> + pthread_attr_t attr;
> + pthread_t thr;
> +
> + sa.sa_flags = SA_SIGINFO;
> +
> + sa.sa_sigaction = sigsegv_handler;
> + sigemptyset(&sa.sa_mask);
> + if (sigaction(SIGSEGV, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + memset(&siginfo, 0, sizeof(siginfo));
> +
> + pthread_attr_init(&attr);
> + pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);
> +
> + pthread_create(&thr, &attr, thread_segv_pkuerr_stack, NULL);
> +
> + pthread_mutex_lock(&mutex);
> + while (siginfo.si_signo == 0)
> + pthread_cond_wait(&cond, &mutex);
> + pthread_mutex_unlock(&mutex);
> +
> + ksft_test_result(siginfo.si_signo == SIGSEGV &&
> + siginfo.si_code == SEGV_PKUERR,
> + "%s\n", __func__);
> +}
> +
> +/*
> + * Verify that the sigsegv handler that uses an alternate signal stack
> + * is correctly invoked for a thread which uses a non-zero MPK to protect
> + * its own stack, and disables all other MPKs (including 0).
> + */
> +static void test_sigsegv_handler_with_different_pkey_for_stack(void)
> +{
> + struct sigaction sa;
> + static stack_t sigstack;
> + void *stack;
> + int pkey;
> + int parent_pid = 0;
> + int child_pid = 0;
> +
> + sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
> +
> + sa.sa_sigaction = sigsegv_handler;
> +
> + sigemptyset(&sa.sa_mask);
> + if (sigaction(SIGSEGV, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
> +     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +
> + assert(stack != MAP_FAILED);
> +
> + /* Allow access to MPK 0 and MPK 1 */
> + __write_pkey_reg(0x55555550);
> +
> + /* Protect the new stack with MPK 1 */
> + pkey = pkey_alloc(0, 0);
> + pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
> +
> + /* Set up alternate signal stack that will use the default MPK */
> + sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
> +      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> + sigstack.ss_flags = 0;
> + sigstack.ss_size = STACK_SIZE;
> +
> + memset(&siginfo, 0, sizeof(siginfo));
> +
> + /* Use clone to avoid newer glibcs using rseq on new threads */
> + long ret = syscall_raw(SYS_clone,
> +       CLONE_VM | CLONE_FS | CLONE_FILES |
> +       CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
> +       CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
> +       CLONE_DETACHED,
> +       (long) ((char *)(stack) + STACK_SIZE),
> +       (long) &parent_pid,
> +       (long) &child_pid, 0, 0);
> +
> + if (ret < 0) {
> + errno = -ret;
> + perror("clone");
> + } else if (ret == 0) {
> + thread_segv_maperr_ptr(&sigstack);
> + syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
> + }
> +
> + pthread_mutex_lock(&mutex);
> + while (siginfo.si_signo == 0)
> + pthread_cond_wait(&cond, &mutex);
> + pthread_mutex_unlock(&mutex);
> +
> + ksft_test_result(siginfo.si_signo == SIGSEGV &&
> + siginfo.si_code == SEGV_MAPERR &&
> + siginfo.si_addr == (void *)1,
> + "%s\n", __func__);
> +}
> +
> +/*
> + * Verify that the PKRU value set by the application is correctly
> + * restored upon return from signal handling.
> + */
> +static void test_pkru_preserved_after_sigusr1(void)
> +{
> + struct sigaction sa;
> + unsigned long pkru = 0x45454544;
> +
> + sa.sa_flags = SA_SIGINFO;
> +
> + sa.sa_sigaction = sigusr1_handler;
> + sigemptyset(&sa.sa_mask);
> + if (sigaction(SIGUSR1, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + memset(&siginfo, 0, sizeof(siginfo));
> +
> + __write_pkey_reg(pkru);
> +
> + raise(SIGUSR1);
> +
> + pthread_mutex_lock(&mutex);
> + while (siginfo.si_signo == 0)
> + pthread_cond_wait(&cond, &mutex);
> + pthread_mutex_unlock(&mutex);
> +
> + /* Ensure the pkru value is the same after returning from signal. */
> + ksft_test_result(pkru == __read_pkey_reg() &&
> + siginfo.si_signo == SIGUSR1,
> + "%s\n", __func__);
> +}
> +
> +static noinline void *thread_sigusr2_self(void *ptr)
> +{
> + /*
> + * A const char array like "Resuming after SIGUSR2" won't be stored on
> + * the stack and the code could access it via an offset from the program
> + * counter. This makes sure it's on the function's stack frame
> + * so we know where it is even when the code is copied.
> + */
> + char str[] = {'R', 'e', 's', 'u', 'm', 'i', 'n', 'g', ' ',
> + 'a', 'f', 't', 'e', 'r', ' ',
> + 'S', 'I', 'G', 'U', 'S', 'R', '2',
> + '.', '.', '.', '\n', '\0'};
> + stack_t *stack = ptr;
> +
> + /*
> + * Setup alternate signal stack, which should be pkey_mprotect()ed by
> + * MPK 0. The thread's stack cannot be used for signals because it is
> + * not accessible by the default init_pkru value of 0x55555554.
> + */
> + syscall(SYS_sigaltstack, (long)stack, 0, 0, 0, 0, 0);
> +
> + /* Disable MPK 0.  Only MPK 2 is enabled. */
> + __write_pkey_reg(0x55555545);
> +
> + raise_sigusr2();
> +
> + /* Do something, to show the thread resumed execution after the signal */
> + syscall_raw(SYS_write, 1, (long) str, sizeof(str) - 1, 0, 0, 0);
> +
> + /*
> + * We can't return to test_pkru_sigreturn because it
> + * will attempt to use a %rbp value which is on the stack
> + * of the main thread.
> + */
> + syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
> + return NULL;
> +}
> +
> +/*
> + * Verify that sigreturn is able to restore altstack even if the thread had
> + * disabled pkey 0.
> + */
> +static void test_pkru_sigreturn(void)
> +{
> + struct sigaction sa = {0};
> + static stack_t sigstack;
> + void *stack;
> + int pkey;
> + int parent_pid = 0;
> + int child_pid = 0;
> +
> + sa.sa_handler = SIG_DFL;
> + sa.sa_flags = 0;
> + sigemptyset(&sa.sa_mask);
> +
> + /*
> + * For this testcase, we do not want to handle SIGSEGV. Reset handler
> + * to default so that the application can crash if it receives SIGSEGV.
> + */
> + if (sigaction(SIGSEGV, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + sa.sa_flags = SA_SIGINFO | SA_ONSTACK;
> + sa.sa_sigaction = sigusr2_handler;
> + sigemptyset(&sa.sa_mask);
> +
> + if (sigaction(SIGUSR2, &sa, NULL) == -1) {
> + perror("sigaction");
> + exit(EXIT_FAILURE);
> + }
> +
> + stack = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE,
> +     MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> +
> + assert(stack != MAP_FAILED);
> +
> + /*
> + * Allow access to MPK 0 and MPK 2. The child thread (to be created
> + * later in this flow) will have its stack protected by MPK 2, whereas
> + * the current thread's stack is protected by the default MPK 0. Hence
> + * both need to be enabled.
> + */
> + __write_pkey_reg(0x55555544);
> +
> + /* Protect the stack with MPK 2 */
> + pkey = pkey_alloc(0, 0);
> + pkey_mprotect(stack, STACK_SIZE, PROT_READ | PROT_WRITE, pkey);
> +
> + /* Set up alternate signal stack that will use the default MPK */
> + sigstack.ss_sp = mmap(0, STACK_SIZE, PROT_READ | PROT_WRITE | PROT_EXEC,
> +      MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> + sigstack.ss_flags = 0;
> + sigstack.ss_size = STACK_SIZE;
> +
> + /* Use clone to avoid newer glibcs using rseq on new threads */
> + long ret = syscall_raw(SYS_clone,
> +       CLONE_VM | CLONE_FS | CLONE_FILES |
> +       CLONE_SIGHAND | CLONE_THREAD | CLONE_SYSVSEM |
> +       CLONE_PARENT_SETTID | CLONE_CHILD_CLEARTID |
> +       CLONE_DETACHED,
> +       (long) ((char *)(stack) + STACK_SIZE),
> +       (long) &parent_pid,
> +       (long) &child_pid, 0, 0);
> +
> + if (ret < 0) {
> + errno = -ret;
> + perror("clone");
> + }  else if (ret == 0) {
> + thread_sigusr2_self(&sigstack);
> + syscall_raw(SYS_exit, 0, 0, 0, 0, 0, 0);
> + }
> +
> + child_pid =  ret;
> + /* Check that thread exited */
> + do {
> + sched_yield();
> + ret = syscall_raw(SYS_tkill, child_pid, 0, 0, 0, 0, 0);
> + } while (ret != -ESRCH && ret != -EINVAL);
> +
> + ksft_test_result_pass("%s\n", __func__);
> +}
> +
> +void (*pkey_tests[])(void) = {
> + test_sigsegv_handler_with_pkey0_disabled,
> + test_sigsegv_handler_cannot_access_stack,
> + test_sigsegv_handler_with_different_pkey_for_stack,
> + test_pkru_preserved_after_sigusr1,
> + test_pkru_sigreturn
> +};
> +
> +int main(int argc, char *argv[])
> +{
> + int i;
> +
> + ksft_print_header();
> + ksft_set_plan(ARRAY_SIZE(pkey_tests));
> +
> + for (i = 0; i < ARRAY_SIZE(pkey_tests); i++)
> + (*pkey_tests[i])();
> +
> + ksft_finished();
> + return 0;
> +}
> diff --git a/tools/testing/selftests/mm/protection_keys.c b/tools/testing/selftests/mm/protection_keys.c
> index 48dc151f8fca..2af344e55d37 100644
> --- a/tools/testing/selftests/mm/protection_keys.c
> +++ b/tools/testing/selftests/mm/protection_keys.c
> @@ -950,16 +950,6 @@ void close_test_fds(void)
> nr_test_fds = 0;
> }
> 
> -#define barrier() __asm__ __volatile__("": : :"memory")
> -__attribute__((noinline)) int read_ptr(int *ptr)
> -{
> - /*
> - * Keep GCC from optimizing this away somehow
> - */
> - barrier();
> - return *ptr;
> -}
> -
> void test_pkey_alloc_free_attach_pkey0(int *ptr, u16 pkey)
> {
> int i, err;
> -- 
> 2.39.3
> 

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