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@xxxxxxx>
---
.../selftests/arm64/signal/test_signals.h | 4 +
.../arm64/signal/test_signals_utils.c | 91 +++++++++++++++++++
.../arm64/signal/test_signals_utils.h | 2 +
.../arm64/signal/testcases/.gitignore | 1 +
.../testcases/mangle_pstate_ssbs_regs.c | 56 ++++++++++++
5 files changed, 154 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 203deac4aa8a..ac438fd123f1 100644
--- a/tools/testing/selftests/arm64/signal/test_signals_utils.c
+++ b/tools/testing/selftests/arm64/signal/test_signals_utils.c
@@ -17,6 +17,8 @@
extern struct tdescr *current;
+static int sig_copyctx = SIGUSR2;
+
static char *feats_store[FMAX_END] = {
"SSBS",
"PAN",
@@ -37,6 +39,85 @@ 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;
@@ -91,6 +172,12 @@ 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;
+ SAFE_WRITE(2,
+ "GOOD CONTEXT grabbed from sig_copyctx handler\n");
} else {
if (signum == current->sig_unsupp && !are_feats_ok(current)) {
SAFE_WRITE(2, "-- RX SIG_UNSUPP on unsupported feature...OK\n");
@@ -193,6 +280,10 @@ 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 7d80a478bad9..b37167c98ccd 100644
--- a/tools/testing/selftests/arm64/signal/test_signals_utils.h
+++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h
@@ -25,4 +25,6 @@ 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,
+};
--
2.17.1
