On 09/10/2019 12:32, Dave Martin wrote:
On Wed, Oct 09, 2019 at 09:26:05AM +0100, Cristian Marussi wrote:
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.
Reviewed-by: Dave Martin Dave.Martin@arm.com
Thanks
Cristian
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");@@ -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:
- grab a valid sigcontext into td->live_uc for result analysis: in
- such case it returns 1.
- 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
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