Introduce a new common utility function get_current_context() which can be used to grab a ucontext without the help of libc, and also to detect if such ucontext has been successfully used by placing it on the stack as a fake sigframe.
Signed-off-by: Cristian Marussi cristian.marussi@arm.com --- v7 --> v8 - added new in v8 (splitted out from v7 05/11) --- .../selftests/arm64/signal/test_signals.h | 6 +- .../arm64/signal/test_signals_utils.c | 31 ++++++ .../arm64/signal/test_signals_utils.h | 98 +++++++++++++++++++ 3 files changed, 134 insertions(+), 1 deletion(-)
diff --git a/tools/testing/selftests/arm64/signal/test_signals.h b/tools/testing/selftests/arm64/signal/test_signals.h index 901521188202..4fd3ba01e3b1 100644 --- a/tools/testing/selftests/arm64/signal/test_signals.h +++ b/tools/testing/selftests/arm64/signal/test_signals.h @@ -88,8 +88,12 @@ 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 sig_atomic_t live_uc_valid; /* optional test private data */ - void *priv; + void *priv;
/* a custom setup: called alternatively to default_setup */ 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 e8bbe36c2660..222148568adf 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.c +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.c @@ -11,14 +11,19 @@ #include <linux/auxvec.h> #include <ucontext.h>
+#include <asm/unistd.h> + #include <kselftest.h>
#include "test_signals.h" #include "test_signals_utils.h" #include "testcases/testcases.h"
+ extern struct tdescr *current;
+static int sig_copyctx = SIGTRAP; + static char const *const feats_names[FMAX_END] = { " SSBS ", " PAN ", @@ -156,6 +161,20 @@ static bool handle_signal_ok(struct tdescr *td, return true; }
+static bool handle_signal_copyctx(struct tdescr *td, + siginfo_t *si, void *uc) +{ + /* Mangling PC to avoid loops on original BRK instr */ + ((ucontext_t *)uc)->uc_mcontext.pc += 4; + memcpy(td->live_uc, uc, td->live_sz); + ASSERT_GOOD_CONTEXT(td->live_uc); + td->live_uc_valid = 1; + fprintf(stderr, + "GOOD CONTEXT grabbed from sig_copyctx handler\n"); + + return true; +} + static void default_handler(int signum, siginfo_t *si, void *uc) { if (current->sig_unsupp && signum == current->sig_unsupp && @@ -167,6 +186,9 @@ static void default_handler(int signum, siginfo_t *si, void *uc) } 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 && + handle_signal_copyctx(current, si, uc)) { + fprintf(stderr, "Handled SIG_COPYCTX\n"); } else { if (signum == SIGALRM && current->timeout) { fprintf(stderr, "-- Timeout !\n"); @@ -221,6 +243,15 @@ static inline int default_trigger(struct tdescr *td)
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; diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h index 5e3a2b7aaa8b..fd67b1f23c41 100644 --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h @@ -4,6 +4,10 @@ #ifndef __TEST_SIGNALS_UTILS_H__ #define __TEST_SIGNALS_UTILS_H__
+#include <assert.h> +#include <stdio.h> +#include <string.h> + #include "test_signals.h"
int test_init(struct tdescr *td); @@ -17,4 +21,98 @@ static inline bool feats_ok(struct tdescr *td) return (td->feats_required & td->feats_supported) == td->feats_required; }
+/* + * 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) +{ + static volatile bool seen_already; + + assert(td && dest_uc); + /* it's a genuine invocation..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 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