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 C91ACECE58D for ; Wed, 9 Oct 2019 11:33:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A0B8F21835 for ; Wed, 9 Oct 2019 11:33:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725962AbfJILdB (ORCPT ); Wed, 9 Oct 2019 07:33:01 -0400 Received: from foss.arm.com ([217.140.110.172]:60362 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729699AbfJILdB (ORCPT ); Wed, 9 Oct 2019 07:33:01 -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 5AAEF28; Wed, 9 Oct 2019 04:33:00 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 732CA3F703; Wed, 9 Oct 2019 04:32:59 -0700 (PDT) Date: Wed, 9 Oct 2019 12:32:57 +0100 From: Dave Martin To: Cristian Marussi Cc: linux-kselftest@vger.kernel.org, linux-arm-kernel@lists.infradead.org, shuah@kernel.org, amit.kachhap@arm.com, andreyknvl@google.com Subject: Re: [PATCH v8 06/12] kselftest: arm64: add helper get_current_context Message-ID: <20191009113256.GD27757@arm.com> References: <20191009082611.9441-1-cristian.marussi@arm.com> <20191009082611.9441-7-cristian.marussi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191009082611.9441-7-cristian.marussi@arm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kselftest-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org 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 > > 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