Added a simple mangle testcase which messes with the ucontext_t from within the sig_handler, trying to toggle PSTATE SSBS bit. Expect SIGILL if SSBS feature unsupported or that the value set in PSTATE.SSBS is preserved on test PASS.
This commit also introduces a new common utility function: get_current_context() which can be used to grab a ucontext without the help of libc, and detect if such ucontext has been actively used to jump back into it.
Signed-off-by: Cristian Marussi cristian.marussi@arm.com --- .../selftests/arm64/signal/test_signals.h | 4 + .../arm64/signal/test_signals_utils.c | 93 +++++++++++++++++++ .../arm64/signal/test_signals_utils.h | 2 + .../arm64/signal/testcases/.gitignore | 1 + .../testcases/mangle_pstate_ssbs_regs.c | 56 +++++++++++ 5 files changed, 156 insertions(+) create mode 100644 tools/testing/selftests/arm64/signal/testcases/mangle_pstate_ssbs_regs.c
diff --git a/tools/testing/selftests/arm64/signal/test_signals.h b/tools/testing/selftests/arm64/signal/test_signals.h index 85db3ac44b32..37bed0590226 100644 --- a/tools/testing/selftests/arm64/signal/test_signals.h +++ b/tools/testing/selftests/arm64/signal/test_signals.h @@ -116,6 +116,10 @@ struct tdescr { /* 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 bool live_uc_valid;
/* a setup function to be called before test starts */ int (*setup)(struct tdescr *td); diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.c b/tools/testing/selftests/arm64/signal/test_signals_utils.c index ac0055f6340b..faf55ba99d58 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.c +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.c @@ -11,12 +11,16 @@ #include <linux/auxvec.h> #include <ucontext.h>
+#include <asm/unistd.h> + #include "test_signals.h" #include "test_signals_utils.h" #include "testcases/testcases.h"
extern struct tdescr *current;
+static int sig_copyctx = SIGUSR2; + static char *feats_store[FMAX_END] = { "SSBS", "PAN", @@ -37,6 +41,85 @@ static inline char *feats_to_string(unsigned long feats) return feats_string; }
+/* + * 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. + * + * 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 the 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 hittig a SEGV. + */ +bool get_current_context(struct tdescr *td, ucontext_t *dest_uc) +{ + static volatile sig_atomic_t seen_already; + + if (!td || !dest_uc) { + fprintf(stdout, "Signal-based Context dumping NOT available\n"); + return 0; + } + + /* it's a genuine invokation..reinit */ + seen_already = 0; + td->live_uc_valid = 0; + td->live_sz = sizeof(*dest_uc); + memset(dest_uc, 0x00, td->live_sz); + td->live_uc = dest_uc; + /* + * Grab ucontext_t triggering a signal... + * ASM equivalent of raise(sig_copyctx); + * + * Note that: + * - live_uc_valid is declared volatile in struct tdescr + * since it will be changed inside the sig_copyctx handler. + * - the kill() syscall invocation returns only after any possible + * registered sig_handler for the invoked signal has returned, + * so that live_uc_valid flag is surely up to date when this + * function return it. + * - the additional 'memory' clobber is there to avoid possible + * compiler's assumption on the content pointed by dest_uc, which + * is changed inside the handler, but not referenced here anyway. + */ + asm volatile ("mov x8, %0\n\t" + "svc #0\n\t" + "mov x1, %1\n\t" + "mov x8, %2\n\t" + "svc #0" + : + : "i" (__NR_getpid), + "r" (sig_copyctx), + "i" (__NR_kill) + : "x1","x8","x0","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 the live_uc has not + * just been acquired...so return 0 + */ + if (seen_already) { + fprintf(stdout, + "Successful sigreturn detected: live_uc is stale !\n"); + return 0; + } + seen_already = 1; + + return td->live_uc_valid; +} + static void unblock_signal(int signum) { sigset_t sset; @@ -112,6 +195,12 @@ static void default_handler(int signum, siginfo_t *si, void *uc) * to terminate immediately exiting straight away */ default_result(current, 1); + } else if (signum == sig_copyctx && current->live_uc) { + memcpy(current->live_uc, uc, current->live_sz); + ASSERT_GOOD_CONTEXT(current->live_uc); + current->live_uc_valid = 1; + fprintf(stderr, + "GOOD CONTEXT grabbed from sig_copyctx handler\n"); } else { if (signum == current->sig_unsupp && !are_feats_ok(current)) { fprintf(stderr, "-- RX SIG_UNSUPP on unsupported feature...OK\n"); @@ -214,6 +303,10 @@ static int test_init(struct tdescr *td) !feats_ok ? "NOT " : ""); }
+ if (td->sig_trig == sig_copyctx) + sig_copyctx = SIGUSR1; + unblock_signal(sig_copyctx); + td->initialized = 1; return 1; } diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index 8658d1a7d4b9..ce35be8ebc8e 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -10,4 +10,6 @@ int test_setup(struct tdescr *td); void test_cleanup(struct tdescr *td); int test_run(struct tdescr *td); void test_result(struct tdescr *td); + +bool get_current_context(struct tdescr *td, ucontext_t *dest_uc); #endif diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore index 226bb179b673..a48a118b1a1a 100644 --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore @@ -3,3 +3,4 @@ mangle_pstate_invalid_daif_bits mangle_pstate_invalid_mode_el1 mangle_pstate_invalid_mode_el2 mangle_pstate_invalid_mode_el3 +mangle_pstate_ssbs_regs diff --git a/tools/testing/selftests/arm64/signal/testcases/mangle_pstate_ssbs_regs.c b/tools/testing/selftests/arm64/signal/testcases/mangle_pstate_ssbs_regs.c new file mode 100644 index 000000000000..a399d9aa40d5 --- /dev/null +++ b/tools/testing/selftests/arm64/signal/testcases/mangle_pstate_ssbs_regs.c @@ -0,0 +1,56 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* Copyright (C) 2019 ARM Limited */ + +#include <stdio.h> +#include <ucontext.h> + +#include "test_signals_utils.h" +#include "testcases.h" + +static int mangle_invalid_pstate_ssbs_run(struct tdescr *td, + siginfo_t *si, ucontext_t *uc) +{ + ASSERT_GOOD_CONTEXT(uc); + + /* set bit value */ + uc->uc_mcontext.pstate |= PSR_SSBS_BIT; + fprintf(stderr, "SSBS set to 1 -- PSTATE: 0x%016lX\n", + uc->uc_mcontext.pstate); + /* Save after mangling...it should be preserved */ + td->saved_uc = *uc; + + return 1; +} + +static void pstate_ssbs_bit_checks(struct tdescr *td) +{ + uint64_t val = 0; + ucontext_t uc; + + /* This check reports some result even if MRS SSBS unsupported */ + if (get_current_context(td, &uc)) + fprintf(stderr, + "INFO: live_uc - got PSTATE: 0x%016lX -> SSBS %s\n", + uc.uc_mcontext.pstate, + (td->saved_uc.uc_mcontext.pstate & PSR_SSBS_BIT) == + (uc.uc_mcontext.pstate & PSR_SSBS_BIT) ? + "PRESERVED" : "CLEARED"); + + fprintf(stderr, "Checking with MRS SSBS...\n"); + get_regval(S3_MRS_SSBS_SYSREG, val); + fprintf(stderr, "INFO: MRS SSBS - got: 0x%016lX\n", val); + /* pass when preserved */ + td->pass = (val & PSR_SSBS_BIT) == + (td->saved_uc.uc_mcontext.pstate & PSR_SSBS_BIT); +} + +struct tdescr tde = { + .sanity_disabled = true, + .name = "MANGLE_PSTATE_SSBS_REGS", + .descr = "Mangling uc_mcontext changing SSBS.(PRESERVE)", + .feats_required = FEAT_SSBS, + .sig_trig = SIGUSR1, + .sig_unsupp = SIGILL, + .run = mangle_invalid_pstate_ssbs_run, + .check_result = pstate_ssbs_bit_checks, +};