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=-8.3 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 91034C4CEC9 for ; Tue, 17 Sep 2019 16:06:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C92721897 for ; Tue, 17 Sep 2019 16:06:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728604AbfIQQGH (ORCPT ); Tue, 17 Sep 2019 12:06:07 -0400 Received: from foss.arm.com ([217.140.110.172]:58124 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727865AbfIQQGG (ORCPT ); Tue, 17 Sep 2019 12:06:06 -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 0CD4515A2; Tue, 17 Sep 2019 09:06:06 -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 25C213F575; Tue, 17 Sep 2019 09:06:05 -0700 (PDT) Date: Tue, 17 Sep 2019 17:06:03 +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 v6 06/11] kselftest: arm64: fake_sigreturn_bad_magic Message-ID: <20190917160603.GN27757@arm.com> References: <20190910123111.33478-1-cristian.marussi@arm.com> <20190910123111.33478-7-cristian.marussi@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190910123111.33478-7-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 Tue, Sep 10, 2019 at 01:31:06pm +0100, Cristian Marussi wrote: > Add a simple fake_sigreturn testcase which builds a ucontext_t with a bad > magic header and place it onto the stack. Expects a SIGSEGV on test PASS. > > Introduce a common utility assembly trampoline function to invoke a > sigreturn while placing the provided sigframe at wanted alignment and > also an helper to make space when needed inside the sigframe reserved > area. > > Signed-off-by: Cristian Marussi > --- > v5 --> v6 > - fake_sigreturn: cleaned up, avoiding excessive SP misalignments > - fake_sigreturn: better formatting and prologue > - get_starting_header: cleand up and commented > - avoid timeout on failure [...] > diff --git a/tools/testing/selftests/arm64/signal/signals.S b/tools/testing/selftests/arm64/signal/signals.S > new file mode 100644 > index 000000000000..e670f8f2c8de > --- /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" > +call_fmt: > + .asciz "Calling sigreturn with fake sigframe sized:%zd at SP @%08lX\n" > + > +.text > + > +.globl fake_sigreturn > + > +/* fake_sigreturn x0:&sigframe, x1:sigframe_size, x2:misalign_bytes */ > +fake_sigreturn: > + stp x29, x30, [sp, #-16]! > + mov x29, sp > + > + mov x20, x0 > + mov x21, x1 > + mov x22, x2 > + > + /* create space on the stack for fake sigframe 16 bytes-aligned */ > + add x0, x21, x22 > + add x0, x0, #16 > + bic x0, x0, #15 /* round_up(sigframe_size + misalign_bytes, 16) */ If I've figured this out right, x0 as computed here actually looks like round_up(sigframe_size + misalign_bytes + 1, 16) - 1. (n + (m - 1)) & ~(m - 1) is the classic way to round up when m is a power of 2. That's why I originally suggested to add 15. Your code works, but I think it always allocates at least one byte more than needed (?) This is not a huge deal, and better than allocating one byte to few, but it would be good to understand whether this behaviour was intentional or not. > + sub sp, sp, x0 > + add x23, sp, x22 /* new sigframe base with misaligment if any */ > + > + ldr x0, =call_fmt > + mov x1, x21 > + mov x2, x23 > + bl printf > + > + /* memcpy the provided content, while still keeping SP aligned */ > + mov x0, x23 > + 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 possibly observed > + * 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] > + /* finally move SP to misaligned address...if any requested */ > + mov sp, x23 > + > + 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/testcases/testcases.c b/tools/testing/selftests/arm64/signal/testcases/testcases.c > index 1914a01222a1..e3521949b800 100644 > --- a/tools/testing/selftests/arm64/signal/testcases/testcases.c > +++ b/tools/testing/selftests/arm64/signal/testcases/testcases.c > @@ -148,3 +148,49 @@ bool validate_reserved(ucontext_t *uc, size_t resv_sz, char **err) > > return true; > } > + > +/* > + * This function walks through the records inside the provided reserved area > + * trying to find enough space to fit @need_sz bytes: if not enough space is > + * available and an extra_context record is present, it throws away the > + * extra_context record. > + * > + * It returns a pointer to a new header where it is possible to start storing > + * our need_sz bytes. > + * > + * @shead: points to the start of reserved area > + * @need_sz: needed bytes > + * @resv_sz: reserved area size in bytes > + * @offset: if not null, this will be filled with the offset of the return > + * head pointer from @shead > + * > + * @return: pointer to a new head where to start storing need_sz bytes, or > + * NULL if space could not be made available. > + */ That's much clearer now, thanks for that. > +struct _aarch64_ctx *get_starting_head(struct _aarch64_ctx *shead, > + size_t need_sz, size_t resv_sz, > + size_t *offset) > +{ [...] Cheers ---Dave