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 00D2FC3A59B for ; Fri, 30 Aug 2019 14:29:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C044F23427 for ; Fri, 30 Aug 2019 14:29:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727930AbfH3O3e (ORCPT ); Fri, 30 Aug 2019 10:29:34 -0400 Received: from foss.arm.com ([217.140.110.172]:33158 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727857AbfH3O3e (ORCPT ); Fri, 30 Aug 2019 10:29:34 -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 2044A344; Fri, 30 Aug 2019 07:29:33 -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 64F373F703; Fri, 30 Aug 2019 07:29:32 -0700 (PDT) Subject: Re: [PATCH v3 06/11] kselftest: arm64: fake_sigreturn_bad_magic To: Dave Martin Cc: linux-kselftest@vger.kernel.org, linux-arm-kernel@lists.infradead.org, shuah@kernel.org, andreyknvl@google.com References: <20190802170300.20662-1-cristian.marussi@arm.com> <20190802170300.20662-7-cristian.marussi@arm.com> <20190813162523.GD10425@arm.com> From: Cristian Marussi Message-ID: <245a3d64-2790-1768-94ab-d1ea56aa3d3d@arm.com> Date: Fri, 30 Aug 2019 15:29:29 +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: <20190813162523.GD10425@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 Hi On 13/08/2019 17:25, Dave Martin wrote: > On Fri, Aug 02, 2019 at 06:02:55PM +0100, Cristian Marussi wrote: >> Added a simple fake_sigreturn testcase which builds a ucontext_t > > Add Ok > >> with a bad magic header and place it onto the stack. >> Expects a SIGSEGV on test PASS. >> This commit also introduces a common utility assembly function to >> invoke a sigreturn using a fake provided sigframe. >> >> Signed-off-by: Cristian Marussi >> --- >> tools/testing/selftests/arm64/signal/Makefile | 2 +- >> .../testing/selftests/arm64/signal/signals.S | 64 +++++++++++++++++++ >> .../arm64/signal/test_signals_utils.h | 1 + >> .../arm64/signal/testcases/.gitignore | 1 + >> .../testcases/fake_sigreturn_bad_magic.c | 63 ++++++++++++++++++ >> 5 files changed, 130 insertions(+), 1 deletion(-) >> create mode 100644 tools/testing/selftests/arm64/signal/signals.S >> create mode 100644 tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c >> >> diff --git a/tools/testing/selftests/arm64/signal/Makefile b/tools/testing/selftests/arm64/signal/Makefile >> index 8c8d08be4b0d..b3dcf315b5a4 100644 >> --- a/tools/testing/selftests/arm64/signal/Makefile >> +++ b/tools/testing/selftests/arm64/signal/Makefile >> @@ -80,7 +80,7 @@ endif >> # Common test-unit targets to build common-layout test-cases executables >> # Needs secondary expansion to properly include the testcase c-file in pre-reqs >> .SECONDEXPANSION: >> -$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c $$@.c test_signals.h test_signals_utils.h testcases/testcases.h >> +$(PROGS): test_signals.c test_signals_utils.c testcases/testcases.c signals.S $$@.c test_signals.h test_signals_utils.h testcases/testcases.h >> @if [ ! -d $(khdr_dir) ]; then \ >> echo -n "\n!!! WARNING: $(khdr_dir) NOT FOUND."; \ >> echo "===> Are you sure Kernel Headers have been installed properly ?\n"; \ >> diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S >> new file mode 100644 >> index 000000000000..6262b877400b >> --- /dev/null >> +++ b/tools/testing/selftests/arm64/signal/signals.S >> @@ -0,0 +1,64 @@ >> +/* >> + * SPDX-License-Identifier: GPL-2.0 >> + * Copyright (C) 2019 ARM Limited >> + */ >> + >> +#include >> + >> +.section ".rodata", "a" > > The section name is not usually quoted in .section (though I guess it > works). > Ok >> +call_fmt: >> + .asciz "Calling sigreturn with fake sigframe sized:%zd at calculated SP @%08lX\n" >> + >> +.text >> + >> +.globl fake_sigreturn >> + >> +/* fake_sigreturn x0:&sigframe, x1:sigframe_size, x2:alignment_SP */ >> +fake_sigreturn: >> + mov x20, x0 >> + mov x21, x1 >> + mov x22, x2 >> + mov x23, sp >> + >> + /* create space on the stack for fake sigframe..."x22"-aligned */ >> + mov x0, #0 > > Why to we move 0 into x0? We clobber x0 again in the next instruction: Yes unneeded. >> + add x0, x21, x22 >> + sub x22, x22, #1 >> + bic x0, x0, x22 >> + sub x23, x23, x0 > > Can you explain the logic here? I'm not sure I understand what this is > trying to do exactly. The attempt is to make space on the stack for a x22-bytes-aligned sigframe of at least x21-bytes-size (assuming x22 is power-of-two): - calculate the needed aligned space (sigframe_size + x22) & ~(x22 - 1) - calculate new SP in x23: x3 = sp - needed_aligned_space - later down... move SP to the calculated sp in x23 - copy the provided sigframe on such new SP > I notice you further modify this in patch 11 -- see my comments there, > where I also suggest an alternative way of specifying a misaligned frame > that might be simpler. I've seen your comments on patch 11. I think I'll simplify that as you suggested: patch 11 was meant to add the capability to misalign the sigframe on the SP (which is needed in testcase contained in 11) but in fact is better if I move all of the simplified logic here. >> + >> + ldr x0, =call_fmt >> + mov x1, x21 >> + mov x2, x23 >> + bl printf >> + >> + mov sp, x23 >> + >> + /* now fill it with the provided content... */ >> + mov x0, sp >> + mov x1, x20 >> + mov x2, x21 >> + bl memcpy >> + >> + /* >> + * Here saving a last minute SP to current->token acts as a marker: >> + * if we got here, we are successfully faking a sigreturn; in other >> + * words we are sure no bad fatal signal has been raised till now >> + * for unrelated reasons, so we should consider the possibl observed > > typo: possible (or possibly?) > possibly >> + * fatal signal like SEGV coming from Kernel restore_sigframe() and >> + * triggered as expected from our test-case. >> + * For simplicity this assumes that current field 'token' is laid out >> + * as first in struct tdescr >> + */ >> + ldr x0, current >> + str x23, [x0] >> + /* SP is already pointing back to the just built fake sigframe here */ >> + mov x8, #__NR_rt_sigreturn >> + svc #0 >> + >> + /* >> + * Above sigreturn should not return...looping here leads to a timeout >> + * and ensure proper and clean test failure, instead of jumping around >> + * on a potentially corrupted stack. >> + */ >> + b . >> diff --git a/tools/testing/selftests/arm64/signal/test_signals_utils.h b/tools/testing/selftests/arm64/signal/test_signals_utils.h >> index ce35be8ebc8e..2a71da7e6695 100644 >> --- a/tools/testing/selftests/arm64/signal/test_signals_utils.h >> +++ b/tools/testing/selftests/arm64/signal/test_signals_utils.h >> @@ -12,4 +12,5 @@ int test_run(struct tdescr *td); >> void test_result(struct tdescr *td); >> >> bool get_current_context(struct tdescr *td, ucontext_t *dest_uc); >> +int fake_sigreturn(void *sigframe, size_t sz, int alignment); >> #endif >> diff --git a/tools/testing/selftests/arm64/signal/testcases/.gitignore b/tools/testing/selftests/arm64/signal/testcases/.gitignore >> index a48a118b1a1a..0ea6fdc3765c 100644 >> --- a/tools/testing/selftests/arm64/signal/testcases/.gitignore >> +++ b/tools/testing/selftests/arm64/signal/testcases/.gitignore >> @@ -4,3 +4,4 @@ mangle_pstate_invalid_mode_el1 >> mangle_pstate_invalid_mode_el2 >> mangle_pstate_invalid_mode_el3 >> mangle_pstate_ssbs_regs >> +fake_sigreturn_bad_magic >> diff --git a/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c >> new file mode 100644 >> index 000000000000..b4c063e02a7a >> --- /dev/null >> +++ b/tools/testing/selftests/arm64/signal/testcases/fake_sigreturn_bad_magic.c >> @@ -0,0 +1,63 @@ >> +/* SPDX-License-Identifier: GPL-2.0 */ >> +/* Copyright (C) 2019 ARM Limited */ >> + > > We should probably also include here, since we're using > siginfo_t etc. Yes indeed. It was included via some other headers only. > >> +#include >> +#include >> + >> +#include "test_signals_utils.h" >> +#include "testcases.h" >> + >> +struct fake_sigframe sf; >> + >> +static int fake_sigreturn_bad_magic_run(struct tdescr *td, >> + siginfo_t *si, ucontext_t *uc) >> +{ >> + size_t resv_sz, offset; >> + struct _aarch64_ctx *shead = GET_SF_RESV_HEAD(sf), *head; >> + >> + /* just to fill the ucontext_t with something real */ >> + if (!get_current_context(td, &sf.uc)) >> + return 1; >> + >> + resv_sz = GET_SF_RESV_SIZE(sf); >> + /* >> + * find the terminator, preserving existing headers >> + * and verify amount of spare room in __reserved area. >> + */ >> + head = get_terminator(shead, resv_sz, &offset); >> + /* >> + * try stripping extra_context header when low on space: >> + * we need at least 2*HDR_SZ space ... one for the KSFT_BAD_MAGIC >> + * and the other for the usual terminator. >> + */ >> + if (head && resv_sz - offset < HDR_SZ * 2) { > > Can we factor out this logic for finding space in the signal frame? > > We do pretty much the same thing in all the fake_sigreturn tests... Ok > >> + fprintf(stderr, "Low on space:%zd. Discarding extra_context.\n", >> + resv_sz - offset); >> + head = get_header(shead, EXTRA_MAGIC, resv_sz, &offset); >> + } >> + /* just give up and timeout if still not enough space */ > > Do we actually time out? I don't see where we actually wait, so doesn't > test_run() just fail immediately? > > The same applies to all the other fake_sigreturn tests too. > Right. It is probably a leftover. SIGALRM is used as an extreme measure to kill tests gone bad, but this can happen only once the fake sigframe has been effectively placed on the stack and sigreturned. >> + if (head && resv_sz - offset >= HDR_SZ) { > > Should this be HDR_SZ * 2 again? We need space for the face header and > space to write a terminator after it. I'll fix in the new factored out code. > >> + fprintf(stderr, "Mangling template header. Spare space:%zd\n", >> + resv_sz - offset); >> + /* >> + * use a well known NON existent bad magic...something >> + * we should pretty sure won't be ever defined in Kernel >> + */ >> + head->magic = KSFT_BAD_MAGIC; >> + head->size = HDR_SZ; >> + write_terminator_record(GET_RESV_NEXT_HEAD(head)); >> + >> + ASSERT_BAD_CONTEXT(&sf.uc); >> + fake_sigreturn(&sf, sizeof(sf), 16); >> + } >> + >> + return 1; >> +} > > [...] > > Cheers > ---Dave > Cheers Cristian