[PATCH 2/4] selftests/arm: Add signal tests
Muhammad Usama Anjum
usama.anjum at collabora.com
Sat Apr 6 14:28:06 PDT 2024
On 4/5/24 1:44 PM, Dev Jain wrote:
> This patch introduces two signal tests, and generic test wrappers similar to
> selftests/arm64/signal directory, along with the mangling testcases found
> therein. arm_cpsr, dumped by the kernel to user space in the ucontext structure
> to the signal handler, is mangled with. The kernel must spot this illegal
> attempt and the testcases are expected to terminate via SEGV.
>
> Signed-off-by: Dev Jain <dev.jain at arm.com>
> ---
> .../selftests/arm/signal/test_signals.c | 27 ++
> .../selftests/arm/signal/test_signals.h | 74 +++++
> .../selftests/arm/signal/test_signals_utils.c | 257 ++++++++++++++++++
> .../selftests/arm/signal/test_signals_utils.h | 128 +++++++++
> .../signal/testcases/mangle_cpsr_aif_bits.c | 33 +++
> .../mangle_cpsr_invalid_compat_toggle.c | 29 ++
Too many files/tests in one patch. Break this patch logically into multiple
tests for easy to review and follow.
> 6 files changed, 548 insertions(+)
> create mode 100644 tools/testing/selftests/arm/signal/test_signals.c
> create mode 100644 tools/testing/selftests/arm/signal/test_signals.h
> create mode 100644 tools/testing/selftests/arm/signal/test_signals_utils.c
> create mode 100644 tools/testing/selftests/arm/signal/test_signals_utils.h
> create mode 100644 tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
> create mode 100644 tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c
>
> diff --git a/tools/testing/selftests/arm/signal/test_signals.c b/tools/testing/selftests/arm/signal/test_signals.c
> new file mode 100644
> index 000000000000..1ecf1e9f041c
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/test_signals.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 ARM Limited
> + *
> + * Generic test wrapper for arm signal tests.
> + *
> + * Each test provides its own tde struct tdescr descriptor to link with
> + * this wrapper. Framework provides common helpers.
> + */
> +#include <kselftest.h>
> +
> +#include "test_signals.h"
> +#include "test_signals_utils.h"
> +
> +struct tdescr *current = &tde;
> +
> +int main(int argc, char *argv[])
> +{
> + ksft_print_msg("%s :: %s\n", current->name, current->descr);
> + if (test_setup(current) && test_init(current)) {
> + test_run(current);
> + test_cleanup(current);
> + }
> + test_result(current);
> +
> + return current->result;
> +}
This test isn't TAP compliant. Please make this and all tests TAP
compilant. The 1/4 patch has example of TAP usage.
> diff --git a/tools/testing/selftests/arm/signal/test_signals.h b/tools/testing/selftests/arm/signal/test_signals.h
> new file mode 100644
> index 000000000000..bbd147127d66
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/test_signals.h
> @@ -0,0 +1,74 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2024 ARM Limited */
> +
> +#ifndef __TEST_SIGNALS_H__
> +#define __TEST_SIGNALS_H__
> +
> +#include <signal.h>
> +#include <stdbool.h>
> +#include <ucontext.h>
> +
> +/*
> + * Using ARCH specific and sanitized Kernel headers from the tree.
> + */
> +#include <asm/ptrace.h>
> +#include <asm/hwcap.h>
> +
> +/*
> + * A descriptor used to describe and configure a test case.
> + * Fields with a non-trivial meaning are described inline in the following.
> + */
> +struct tdescr {
> + /* KEEP THIS FIELD FIRST for easier lookup from assembly */
> + void *token;
> + /* when disabled token based sanity checking is skipped in handler */
> + bool sanity_disabled;
> + /* just a name for the test-case; manadatory field */
> + char *name;
> + char *descr;
> +
> + bool initialized;
> + unsigned int minsigstksz;
> + /* signum used as a test trigger. Zero if no trigger-signal is used */
> + int sig_trig;
> + /*
> + * signum considered as a successful test completion.
> + * Zero when no signal is expected on success
> + */
> + int sig_ok;
> + /* signum expected on unsupported CPU features. */
> + int sig_unsupp;
> + /* a timeout in second for test completion */
> + unsigned int timeout;
> + bool triggered;
> + bool pass;
> + unsigned int result;
> + /* optional sa_flags for the installed handler */
> + int sa_flags;
> + ucontext_t saved_uc;
> + /* used by get_current_ctx() */
> + size_t live_sz;
> + ucontext_t *live_uc;
> + volatile sig_atomic_t live_uc_valid;
> + /* optional test private data */
> + void *priv;
> +
> + /* a custom setup: called alternatively to default_setup */
> + int (*setup)(struct tdescr *td);
> + /* a custom init: called by default test init after test_setup */
> + bool (*init)(struct tdescr *td);
> + /* a custom cleanup function called before test exits */
> + void (*cleanup)(struct tdescr *td);
> + /* an optional function to be used as a trigger for starting test */
> + int (*trigger)(struct tdescr *td);
> + /*
> + * the actual test-core: invoked differently depending on the
> + * presence of the trigger function above; this is mandatory
> + */
> + int (*run)(struct tdescr *td, siginfo_t *si, ucontext_t *uc);
> + /* an optional function for custom results' processing */
> + void (*check_result)(struct tdescr *td);
> +};
> +
> +extern struct tdescr tde;
> +#endif
> diff --git a/tools/testing/selftests/arm/signal/test_signals_utils.c b/tools/testing/selftests/arm/signal/test_signals_utils.c
> new file mode 100644
> index 000000000000..96aeb11de151
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/test_signals_utils.c
> @@ -0,0 +1,257 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (C) 2024 ARM Limited */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <signal.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <assert.h>
> +#include <sys/auxv.h>
> +#include <linux/auxvec.h>
> +#include <ucontext.h>
> +
> +#include <asm/unistd.h>
> +
> +#include <kselftest.h>
> +
> +#include "test_signals.h"
> +#include "test_signals_utils.h"
> +
> +
> +extern struct tdescr *current;
> +
> +static int sig_copyctx = SIGTRAP;
> +
> +static void unblock_signal(int signum)
> +{
> + sigset_t sset;
> +
> + sigemptyset(&sset);
> + sigaddset(&sset, signum);
> + sigprocmask(SIG_UNBLOCK, &sset, NULL);
> +}
> +
> +static void default_result(struct tdescr *td, bool force_exit)
> +{
> + if (td->result == KSFT_SKIP) {
> + fprintf(stderr, "==>> completed. SKIP.\n");
> + } else if (td->pass) {
> + fprintf(stderr, "==>> completed. PASS(1)\n");
> + td->result = KSFT_PASS;
> + } else {
> + fprintf(stdout, "==>> completed. FAIL(0)\n");
> + td->result = KSFT_FAIL;
> + }
> +
> + if (force_exit)
> + exit(td->result);
> +}
> +
> +/*
> + * The following handle_signal_* helpers are used by main default_handler
> + * and are meant to return true when signal is handled successfully:
> + * when false is returned instead, it means that the signal was somehow
> + * unexpected in that context and it was NOT handled; default_handler will
> + * take care of such unexpected situations.
> + */
> +
> +static bool handle_signal_unsupported(struct tdescr *td,
> + siginfo_t *si, void *uc)
> +{
> +
> + /* Mangling PC to avoid loops on original SIGILL */
> + ((ucontext_t *)uc)->uc_mcontext.arm_pc += 4;
> +
> + if (!td->initialized) {
> + fprintf(stderr,
> + "Got SIG_UNSUPP @test_init. Ignore.\n");
> + } else {
> + fprintf(stderr,
> + "-- RX SIG_UNSUPP on unsupported feat...OK\n");
> + td->pass = 1;
> + default_result(current, 1);
> + }
> +
> + return true;
> +}
> +
> +static bool handle_signal_trigger(struct tdescr *td,
> + siginfo_t *si, void *uc)
> +{
> + td->triggered = 1;
> +
> + /* ->run was asserted NON-NULL in test_setup() already */
> + td->run(td, si, uc);
> +
> + return true;
> +}
> +
> +static bool handle_signal_ok(struct tdescr *td,
> + siginfo_t *si, void *uc)
> +{
> +
> + /*
> + * it's a bug in the test code when this assert fail:
> + * if sig_trig was defined, it must have been used before getting here.
> + */
> + assert(!td->sig_trig || td->triggered);
> + fprintf(stderr,
> + "SIG_OK -- SP:0x%lX si_addr@:%p si_code:%d token@:%p offset:%d\n",
> + ((ucontext_t *)uc)->uc_mcontext.arm_sp,
> + si->si_addr, si->si_code, td->token, td->token - si->si_addr);
> +
> + /*
> + * Trying to narrow down the SEGV to the ones generated by Kernel itself
> + * via arm64_notify_segfault(). This is a best-effort check anyway, and
> + * the si_code check may need to change if this aspect of the kernel
> + * ABI changes.
> + */
> + if (td->sig_ok == SIGSEGV && si->si_code != SEGV_ACCERR) {
> + fprintf(stdout,
> + "si_code != SEGV_ACCERR...test is probably broken!\n");
> + abort();
> + }
> + td->pass = 1;
> + /*
> + * Some tests can lead to SEGV loops: in such a case we want to
> + * terminate immediately exiting straight away; some others are not
> + * supposed to outlive the signal handler code, due to the content of
> + * the fake sigframe which caused the signal itself.
> + */
> + default_result(current, 1);
> +
> + return true;
> +}
> +
> +static void default_handler(int signum, siginfo_t *si, void *uc)
> +{
> + if (current->sig_unsupp && signum == current->sig_unsupp &&
> + handle_signal_unsupported(current, si, uc)) {
> + fprintf(stderr, "Handled SIG_UNSUPP\n");
> + } else if (current->sig_trig && signum == current->sig_trig &&
> + handle_signal_trigger(current, si, uc)) {
> + fprintf(stderr, "Handled SIG_TRIG\n");
> + } else if (current->sig_ok && signum == current->sig_ok &&
> + handle_signal_ok(current, si, uc)) {
> + fprintf(stderr, "Handled SIG_OK\n");
> + } else if (signum == sig_copyctx && current->live_uc) {
> + fprintf(stderr, "Handled SIG_COPYCTX\n");
> + } else {
> + if (signum == SIGALRM && current->timeout) {
> + fprintf(stderr, "-- Timeout !\n");
> + } else {
> + fprintf(stderr,
> + "-- RX UNEXPECTED SIGNAL: %d code %d address %p\n",
> + signum, si->si_code, si->si_addr);
> + }
> + default_result(current, 1);
> + }
> +}
> +
> +static int default_setup(struct tdescr *td)
> +{
> + struct sigaction sa;
> +
> + sa.sa_sigaction = default_handler;
> + sa.sa_flags = SA_SIGINFO | SA_RESTART;
> + sa.sa_flags |= td->sa_flags;
> + sigemptyset(&sa.sa_mask);
> + /* uncatchable signals naturally skipped ... */
> + for (int sig = 1; sig < 32; sig++)
> + sigaction(sig, &sa, NULL);
> + /*
> + * RT Signals default disposition is Term but they cannot be
> + * generated by the Kernel in response to our tests; so just catch
> + * them all and report them as UNEXPECTED signals.
> + */
> + for (int sig = SIGRTMIN; sig <= SIGRTMAX; sig++)
> + sigaction(sig, &sa, NULL);
> +
> + /* just in case...unblock explicitly all we need */
> + if (td->sig_trig)
> + unblock_signal(td->sig_trig);
> + if (td->sig_ok)
> + unblock_signal(td->sig_ok);
> + if (td->sig_unsupp)
> + unblock_signal(td->sig_unsupp);
> +
> + if (td->timeout) {
> + unblock_signal(SIGALRM);
> + alarm(td->timeout);
> + }
> + fprintf(stderr, "Registered handlers for all signals.\n");
> +
> + return 1;
> +}
> +
> +static inline int default_trigger(struct tdescr *td)
> +{
> + return !raise(td->sig_trig);
> +}
> +
> +int test_init(struct tdescr *td)
> +{
> + if (td->sig_trig == sig_copyctx) {
> + fprintf(stdout,
> + "Signal %d is RESERVED, cannot be used as a trigger. Aborting\n",
> + sig_copyctx);
> + return 0;
> + }
> + /* just in case */
> + unblock_signal(sig_copyctx);
> +
> + td->minsigstksz = getauxval(AT_MINSIGSTKSZ);
> + if (!td->minsigstksz)
> + td->minsigstksz = MINSIGSTKSZ;
> + fprintf(stderr, "Detected MINSTKSIGSZ:%d\n", td->minsigstksz);
> +
> + /* Perform test specific additional initialization */
> + if (td->init && !td->init(td)) {
> + fprintf(stderr, "FAILED Testcase initialization.\n");
> + return 0;
> + }
> + td->initialized = 1;
> + fprintf(stderr, "Testcase initialized.\n");
> +
> + return 1;
> +}
> +
> +int test_setup(struct tdescr *td)
> +{
> + /* assert core invariants symptom of a rotten testcase */
> + assert(current);
> + assert(td);
> + assert(td->name);
> + assert(td->run);
> +
> + /* Default result is FAIL if test setup fails */
> + td->result = KSFT_FAIL;
> + if (td->setup)
> + return td->setup(td);
> + else
> + return default_setup(td);
> +}
> +
> +int test_run(struct tdescr *td)
> +{
> + if (td->trigger)
> + return td->trigger(td);
> + else if (td->sig_trig)
> + return default_trigger(td);
> + else
> + return td->run(td, NULL, NULL);
> +}
> +
> +void test_result(struct tdescr *td)
> +{
> + if (td->initialized && td->result != KSFT_SKIP && td->check_result)
> + td->check_result(td);
> + default_result(td, 0);
> +}
> +
> +void test_cleanup(struct tdescr *td)
> +{
> + if (td->cleanup)
> + td->cleanup(td);
> +}
> diff --git a/tools/testing/selftests/arm/signal/test_signals_utils.h b/tools/testing/selftests/arm/signal/test_signals_utils.h
> new file mode 100644
> index 000000000000..386dcc6c268d
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/test_signals_utils.h
> @@ -0,0 +1,128 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2024 ARM Limited */
> +
> +#ifndef __TEST_SIGNALS_UTILS_H__
> +#define __TEST_SIGNALS_UTILS_H__
> +
> +#include <assert.h>
> +#include <stdio.h>
> +#include <string.h>
> +
> +#include <linux/compiler.h>
> +#include "test_signals.h"
> +
> +int test_init(struct tdescr *td);
> +int test_setup(struct tdescr *td);
> +void test_cleanup(struct tdescr *td);
> +int test_run(struct tdescr *td);
> +void test_result(struct tdescr *td);
> +
> +/*
> + * Obtaining a valid and full-blown ucontext_t from userspace is tricky:
> + * libc getcontext does() not save all the regs and messes with some of
> + * them (pstate value in particular is not reliable).
> + *
> + * Here we use a service signal to grab the ucontext_t from inside a
> + * dedicated signal handler, since there, it is populated by Kernel
> + * itself in setup_sigframe(). The grabbed context is then stored and
> + * made available in td->live_uc.
> + *
> + * As service-signal is used a SIGTRAP induced by a 'brk' instruction,
> + * because here we have to avoid syscalls to trigger the signal since
> + * they would cause any SVE sigframe content (if any) to be removed.
> + *
> + * Anyway this function really serves a dual purpose:
> + *
> + * 1. grab a valid sigcontext into td->live_uc for result analysis: in
> + * such case it returns 1.
> + *
> + * 2. detect if, somehow, a previously grabbed live_uc context has been
> + * used actively with a sigreturn: in such a case the execution would have
> + * magically resumed in the middle of this function itself (seen_already==1):
> + * in such a case return 0, since in fact we have not just simply grabbed
> + * the context.
> + *
> + * This latter case is useful to detect when a fake_sigreturn test-case has
> + * unexpectedly survived without hitting a SEGV.
> + *
> + * Note that the case of runtime dynamically sized sigframes (like in SVE
> + * context) is still NOT addressed: sigframe size is supposed to be fixed
> + * at sizeof(ucontext_t).
> + */
> +static __always_inline bool get_current_context(struct tdescr *td,
> + ucontext_t *dest_uc,
> + size_t dest_sz)
> +{
> + static volatile bool seen_already;
> + int i;
> + char *uc = (char *)dest_uc;
> +
> + assert(td && dest_uc);
> + /* it's a genuine invocation..reinit */
> + seen_already = 0;
> + td->live_uc_valid = 0;
> + td->live_sz = dest_sz;
> +
> + /*
> + * This is a memset() but we don't want the compiler to
> + * optimise it into either instructions or a library call
> + * which might be incompatible with streaming mode.
> + */
> + for (i = 0; i < td->live_sz; i++) {
> + uc[i] = 0;
> + OPTIMIZER_HIDE_VAR(uc[0]);
> + }
> +
> + td->live_uc = dest_uc;
> + /*
> + * Grab ucontext_t triggering a SIGTRAP.
> + *
> + * Note that:
> + * - live_uc_valid is declared volatile sig_atomic_t in
> + * struct tdescr since it will be changed inside the
> + * sig_copyctx handler
> + * - the additional 'memory' clobber is there to avoid possible
> + * compiler's assumption on live_uc_valid and the content
> + * pointed by dest_uc, which are all changed inside the signal
> + * handler
> + * - BRK causes a debug exception which is handled by the Kernel
> + * and finally causes the SIGTRAP signal to be delivered to this
> + * test thread. Since such delivery happens on the ret_to_user()
> + * /do_notify_resume() debug exception return-path, we are sure
> + * that the registered SIGTRAP handler has been run to completion
> + * before the execution path is restored here: as a consequence
> + * we can be sure that the volatile sig_atomic_t live_uc_valid
> + * carries a meaningful result. Being in a single thread context
> + * we'll also be sure that any access to memory modified by the
> + * handler (namely ucontext_t) will be visible once returned.
> + * - note that since we are using a breakpoint instruction here
> + * to cause a SIGTRAP, the ucontext_t grabbed from the signal
> + * handler would naturally contain a PC pointing exactly to this
> + * BRK line, which means that, on return from the signal handler,
> + * or if we place the ucontext_t on the stack to fake a sigreturn,
> + * we'll end up in an infinite loop of BRK-SIGTRAP-handler.
> + * For this reason we take care to artificially move forward the
> + * PC to the next instruction while inside the signal handler.
> + */
> + asm volatile ("brk #666"
> + : "+m" (*dest_uc)
> + :
> + : "memory");
> +
> + /*
> + * If we get here with seen_already==1 it implies the td->live_uc
> + * context has been used to get back here....this probably means
> + * a test has failed to cause a SEGV...anyway live_uc does not
> + * point to a just acquired copy of ucontext_t...so return 0
> + */
> + if (seen_already) {
> + fprintf(stdout,
> + "Unexpected successful sigreturn detected: live_uc is stale !\n");
> + return 0;
> + }
> + seen_already = 1;
> +
> + return td->live_uc_valid;
> +}
> +
> +#endif
> diff --git a/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
> new file mode 100644
> index 000000000000..f422cd11ccf2
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_aif_bits.c
> @@ -0,0 +1,33 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 ARM Limited
> + *
> + * Try to mangle the ucontext from inside a signal handler, mangling the
> + * AIF bits in an illegal manner: this attempt must be spotted by Kernel
> + * and the test case is expected to be terminated via SEGV.
> + *
> + */
> +
> +#include "test_signals_utils.h"
> +
> +static int mangle_invalid_cpsr_run(struct tdescr *td, siginfo_t *si,
> + ucontext_t *uc)
> +{
> +
> + /*
> + * This config should trigger a SIGSEGV by Kernel when it checks
> + * the sigframe consistency in valid_user_regs() routine.
> + */
> + uc->uc_mcontext.arm_cpsr |= PSR_A_BIT | PSR_I_BIT | PSR_F_BIT;
> +
> + return 1;
> +}
> +
> +struct tdescr tde = {
> + .sanity_disabled = true,
> + .name = "MANGLE_CPSR_INVALID_AIF_BITS",
> + .descr = "Mangling uc_mcontext with INVALID AIF_BITS",
> + .sig_trig = SIGUSR1,
> + .sig_ok = SIGSEGV,
> + .run = mangle_invalid_cpsr_run,
> +};
> diff --git a/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c
> new file mode 100644
> index 000000000000..cb7eb8aec7f2
> --- /dev/null
> +++ b/tools/testing/selftests/arm/signal/testcases/mangle_cpsr_invalid_compat_toggle.c
> @@ -0,0 +1,29 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) 2024 ARM Limited
> + *
> + * Try to mangle the ucontext from inside a signal handler, toggling
> + * the execution state bit: this attempt must be spotted by Kernel and
> + * the test case is expected to be terminated via SEGV.
> + */
> +
> +#include "test_signals_utils.h"
> +
> +static int mangle_invalid_cpsr_run(struct tdescr *td, siginfo_t *si,
> + ucontext_t *uc)
> +{
> +
> + /* This config should trigger a SIGSEGV by Kernel */
> + uc->uc_mcontext.arm_cpsr ^= MODE32_BIT;
> +
> + return 1;
> +}
> +
> +struct tdescr tde = {
> + .sanity_disabled = true,
> + .name = "MANGLE_CPSR_INVALID_STATE_TOGGLE",
> + .descr = "Mangling uc_mcontext with INVALID STATE_TOGGLE",
> + .sig_trig = SIGUSR1,
> + .sig_ok = SIGSEGV,
> + .run = mangle_invalid_cpsr_run,
> +};
--
BR,
Muhammad Usama Anjum
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