From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2AB7EC47404 for ; Wed, 9 Oct 2019 11:58:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ED32A21848 for ; Wed, 9 Oct 2019 11:58:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727228AbfJIL6B (ORCPT ); Wed, 9 Oct 2019 07:58:01 -0400 Received: from foss.arm.com ([217.140.110.172]:60806 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727002AbfJIL6B (ORCPT ); Wed, 9 Oct 2019 07:58:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 59A9428; Wed, 9 Oct 2019 04:58:00 -0700 (PDT) Received: from [10.1.197.50] (e120937-lin.cambridge.arm.com [10.1.197.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 8B3EE3F703; Wed, 9 Oct 2019 04:57:59 -0700 (PDT) Subject: Re: [PATCH v8 06/12] kselftest: arm64: add helper get_current_context To: Dave Martin Cc: linux-kselftest@vger.kernel.org, linux-arm-kernel@lists.infradead.org, shuah@kernel.org, amit.kachhap@arm.com, andreyknvl@google.com References: <20191009082611.9441-1-cristian.marussi@arm.com> <20191009082611.9441-7-cristian.marussi@arm.com> <20191009113256.GD27757@arm.com> From: Cristian Marussi Message-ID: Date: Wed, 9 Oct 2019 12:57:58 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20191009113256.GD27757@arm.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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 > Thanks Cristian >> >> Signed-off-by: Cristian Marussi >> --- >> 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 >> #include >> >> +#include >> + >> #include >> >> #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 >> +#include >> +#include >> + >> #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 >> >> >> _______________________________________________ >> linux-arm-kernel mailing list >> linux-arm-kernel@lists.infradead.org >> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel