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@xxxxxxx>
---
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
--
2.17.1
