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=-15.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,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 B4E73C433DB for ; Wed, 27 Jan 2021 15:17:50 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 4952D20780 for ; Wed, 27 Jan 2021 15:17:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4952D20780 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References:Message-ID: Subject:To:From:Date:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=sN9YNftSborywUa/RZGuD89hl+P8mAxhRMOyp29Ci08=; b=f+Ks1g00LLOIS0LPVBEJq4/J8 sn4rNwkQohMzAiQkzqLu/chyP46vAC2v1gAmjLQt/5u2wfeucG6G+J3p0yrbQrxayEeGqH8+n7ZpI RcDmU9GNixc7qhRY3s2OnQPdPCCznIzHWo3Kfx8DDiFMEp78VlR5oCDw4g9hdmSq0dr3xtwHiBFmP I8N9J4v2quO95wBcz4bienJKkOjHHEVf88wa0L0Q1BNNSfELGPQM3JYUtF+3oJjbPnPzZyBCqVTTg K12Q6RGDbDueMPVzUnhoy7gt8tkQu59YhavAOTpEClkOZXhAhSjm7nucIbrNziHvWj5JEM3dVG4vO ZYcvv4zpw==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4mXE-0004AC-UK; Wed, 27 Jan 2021 15:15:08 +0000 Received: from foss.arm.com ([217.140.110.172]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l4mX5-00046q-8D for linux-arm-kernel@lists.infradead.org; Wed, 27 Jan 2021 15:15:00 +0000 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 009AF1042; Wed, 27 Jan 2021 07:14:58 -0800 (PST) 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 197E03F66B; Wed, 27 Jan 2021 07:14:56 -0800 (PST) Date: Wed, 27 Jan 2021 15:14:39 +0000 From: Dave Martin To: Andrei Vagin Subject: Re: [PATCH 1/3] arm64/ptrace: don't clobber task registers on syscall entry/exit traps Message-ID: <20210127151438.GD13952@arm.com> References: <20210119220637.494476-1-avagin@gmail.com> <20210119220637.494476-2-avagin@gmail.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210119220637.494476-2-avagin@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210127_101459_455191_CED54FEB X-CRM114-Status: GOOD ( 32.45 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , Will Deacon , Oleg Nesterov , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Jan 19, 2021 at 02:06:35PM -0800, Andrei Vagin wrote: > ip/r12 for AArch32 and x7 for AArch64 is used to indicate whether or not > the stop has been signalled from syscall entry or syscall exit. This > means that: > > - Any writes by the tracer to this register during the stop are > ignored/discarded. > > - The actual value of the register is not available during the stop, > so the tracer cannot save it and restore it later. > > Right now, these registers are clobbered in tracehook_report_syscall. > This change moves this logic to gpr_get and compat_gpr_get where > registers are copied into a user-space buffer. > > This will allow to change these registers and to introduce a new > NT_ARM_PRSTATUS command to get the full set of registers. > > Signed-off-by: Andrei Vagin > --- > arch/arm64/include/asm/ptrace.h | 5 ++ > arch/arm64/kernel/ptrace.c | 104 +++++++++++++++++++------------- > 2 files changed, 67 insertions(+), 42 deletions(-) > > diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h > index e58bca832dff..0a9552b4f61e 100644 > --- a/arch/arm64/include/asm/ptrace.h > +++ b/arch/arm64/include/asm/ptrace.h > @@ -170,6 +170,11 @@ static inline unsigned long pstate_to_compat_psr(const unsigned long pstate) > return psr; > } > > +enum ptrace_syscall_dir { > + PTRACE_SYSCALL_ENTER = 0, > + PTRACE_SYSCALL_EXIT, > +}; > + > /* > * This struct defines the way the registers are stored on the stack during an > * exception. Note that sizeof(struct pt_regs) has to be a multiple of 16 (for > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > index 8ac487c84e37..1863f080cb07 100644 > --- a/arch/arm64/kernel/ptrace.c > +++ b/arch/arm64/kernel/ptrace.c > @@ -40,6 +40,7 @@ > #include > #include > #include > +#include > > #define CREATE_TRACE_POINTS > #include > @@ -561,7 +562,33 @@ static int gpr_get(struct task_struct *target, > struct membuf to) > { > struct user_pt_regs *uregs = &task_pt_regs(target)->user_regs; > - return membuf_write(&to, uregs, sizeof(*uregs)); > + unsigned long saved_reg; > + int ret; > + > + /* > + * We have some ABI weirdness here in the way that we handle syscall > + * exit stops because we indicate whether or not the stop has been > + * signalled from syscall entry or syscall exit by clobbering the general > + * purpose register x7. > + */ > + switch (target->ptrace_message) { > + case PTRACE_EVENTMSG_SYSCALL_ENTRY: > + saved_reg = uregs->regs[7]; > + uregs->regs[7] = PTRACE_SYSCALL_ENTER; > + break; > + case PTRACE_EVENTMSG_SYSCALL_EXIT: > + saved_reg = uregs->regs[7]; > + uregs->regs[7] = PTRACE_SYSCALL_EXIT; > + break; > + } > + > + ret = membuf_write(&to, uregs, sizeof(*uregs)); > + > + if (target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_ENTRY || > + target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_EXIT) > + uregs->regs[7] = saved_reg; This might be a reasonable cleanup even if the extra regset isn't introduced: it makes it clear that we're not changing the user registers here, just the tracer's view of them. I'm assuming it doesn't break tracing anywhere else. I can't think of anything it would break just now, but I haven't spent much time looking into it. Can you not just unconditionally back up and restore regs[7] here? e.g. saved_reg = uregs->regs[7]; switch (target->ptrace_message) { case PTRACE_EVENTMSG_SYSCALL_ENTRY: case PTRACE_EVENTMSG_SYSCALL_EXIT: uregs->regs[7] = target->ptrace_message; } ret = membuf_write(...); uregs->regs[7] = saved_reg; > + > + return ret; > } > > static int gpr_set(struct task_struct *target, const struct user_regset *regset, > @@ -1221,10 +1248,40 @@ static int compat_gpr_get(struct task_struct *target, > const struct user_regset *regset, > struct membuf to) > { > + compat_ulong_t r12; > + bool overwrite_r12; > int i = 0; > > - while (to.left) > - membuf_store(&to, compat_get_user_reg(target, i++)); > + /* > + * We have some ABI weirdness here in the way that we handle syscall > + * exit stops because we indicate whether or not the stop has been > + * signalled from syscall entry or syscall exit by clobbering the > + * general purpose register r12. > + */ > + switch (target->ptrace_message) { > + case PTRACE_EVENTMSG_SYSCALL_ENTRY: > + r12 = PTRACE_SYSCALL_ENTER; > + overwrite_r12 = true; > + break; > + case PTRACE_EVENTMSG_SYSCALL_EXIT: > + r12 = PTRACE_SYSCALL_EXIT; > + overwrite_r12 = true; > + break; > + default: > + overwrite_r12 = false; > + break; > + } > + > + while (to.left) { > + compat_ulong_t val; > + > + if (!overwrite_r12 || i != 12) > + val = compat_get_user_reg(target, i++); > + else > + val = r12; > + membuf_store(&to, val); > + } > + Can this be condensed too, say by introducing a wrapper for compat_get_user_reg() that does the fudging on r12? [...] Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 8CC32C433E0 for ; Wed, 27 Jan 2021 15:22:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 50075207DE for ; Wed, 27 Jan 2021 15:22:35 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1343849AbhA0PVy (ORCPT ); Wed, 27 Jan 2021 10:21:54 -0500 Received: from foss.arm.com ([217.140.110.172]:50700 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234641AbhA0PPo (ORCPT ); Wed, 27 Jan 2021 10:15:44 -0500 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 009AF1042; Wed, 27 Jan 2021 07:14:58 -0800 (PST) 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 197E03F66B; Wed, 27 Jan 2021 07:14:56 -0800 (PST) Date: Wed, 27 Jan 2021 15:14:39 +0000 From: Dave Martin To: Andrei Vagin Cc: Will Deacon , Catalin Marinas , Oleg Nesterov , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] arm64/ptrace: don't clobber task registers on syscall entry/exit traps Message-ID: <20210127151438.GD13952@arm.com> References: <20210119220637.494476-1-avagin@gmail.com> <20210119220637.494476-2-avagin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210119220637.494476-2-avagin@gmail.com> User-Agent: Mutt/1.5.23 (2014-03-12) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 19, 2021 at 02:06:35PM -0800, Andrei Vagin wrote: > ip/r12 for AArch32 and x7 for AArch64 is used to indicate whether or not > the stop has been signalled from syscall entry or syscall exit. This > means that: > > - Any writes by the tracer to this register during the stop are > ignored/discarded. > > - The actual value of the register is not available during the stop, > so the tracer cannot save it and restore it later. > > Right now, these registers are clobbered in tracehook_report_syscall. > This change moves this logic to gpr_get and compat_gpr_get where > registers are copied into a user-space buffer. > > This will allow to change these registers and to introduce a new > NT_ARM_PRSTATUS command to get the full set of registers. > > Signed-off-by: Andrei Vagin > --- > arch/arm64/include/asm/ptrace.h | 5 ++ > arch/arm64/kernel/ptrace.c | 104 +++++++++++++++++++------------- > 2 files changed, 67 insertions(+), 42 deletions(-) > > diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h > index e58bca832dff..0a9552b4f61e 100644 > --- a/arch/arm64/include/asm/ptrace.h > +++ b/arch/arm64/include/asm/ptrace.h > @@ -170,6 +170,11 @@ static inline unsigned long pstate_to_compat_psr(const unsigned long pstate) > return psr; > } > > +enum ptrace_syscall_dir { > + PTRACE_SYSCALL_ENTER = 0, > + PTRACE_SYSCALL_EXIT, > +}; > + > /* > * This struct defines the way the registers are stored on the stack during an > * exception. Note that sizeof(struct pt_regs) has to be a multiple of 16 (for > diff --git a/arch/arm64/kernel/ptrace.c b/arch/arm64/kernel/ptrace.c > index 8ac487c84e37..1863f080cb07 100644 > --- a/arch/arm64/kernel/ptrace.c > +++ b/arch/arm64/kernel/ptrace.c > @@ -40,6 +40,7 @@ > #include > #include > #include > +#include > > #define CREATE_TRACE_POINTS > #include > @@ -561,7 +562,33 @@ static int gpr_get(struct task_struct *target, > struct membuf to) > { > struct user_pt_regs *uregs = &task_pt_regs(target)->user_regs; > - return membuf_write(&to, uregs, sizeof(*uregs)); > + unsigned long saved_reg; > + int ret; > + > + /* > + * We have some ABI weirdness here in the way that we handle syscall > + * exit stops because we indicate whether or not the stop has been > + * signalled from syscall entry or syscall exit by clobbering the general > + * purpose register x7. > + */ > + switch (target->ptrace_message) { > + case PTRACE_EVENTMSG_SYSCALL_ENTRY: > + saved_reg = uregs->regs[7]; > + uregs->regs[7] = PTRACE_SYSCALL_ENTER; > + break; > + case PTRACE_EVENTMSG_SYSCALL_EXIT: > + saved_reg = uregs->regs[7]; > + uregs->regs[7] = PTRACE_SYSCALL_EXIT; > + break; > + } > + > + ret = membuf_write(&to, uregs, sizeof(*uregs)); > + > + if (target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_ENTRY || > + target->ptrace_message == PTRACE_EVENTMSG_SYSCALL_EXIT) > + uregs->regs[7] = saved_reg; This might be a reasonable cleanup even if the extra regset isn't introduced: it makes it clear that we're not changing the user registers here, just the tracer's view of them. I'm assuming it doesn't break tracing anywhere else. I can't think of anything it would break just now, but I haven't spent much time looking into it. Can you not just unconditionally back up and restore regs[7] here? e.g. saved_reg = uregs->regs[7]; switch (target->ptrace_message) { case PTRACE_EVENTMSG_SYSCALL_ENTRY: case PTRACE_EVENTMSG_SYSCALL_EXIT: uregs->regs[7] = target->ptrace_message; } ret = membuf_write(...); uregs->regs[7] = saved_reg; > + > + return ret; > } > > static int gpr_set(struct task_struct *target, const struct user_regset *regset, > @@ -1221,10 +1248,40 @@ static int compat_gpr_get(struct task_struct *target, > const struct user_regset *regset, > struct membuf to) > { > + compat_ulong_t r12; > + bool overwrite_r12; > int i = 0; > > - while (to.left) > - membuf_store(&to, compat_get_user_reg(target, i++)); > + /* > + * We have some ABI weirdness here in the way that we handle syscall > + * exit stops because we indicate whether or not the stop has been > + * signalled from syscall entry or syscall exit by clobbering the > + * general purpose register r12. > + */ > + switch (target->ptrace_message) { > + case PTRACE_EVENTMSG_SYSCALL_ENTRY: > + r12 = PTRACE_SYSCALL_ENTER; > + overwrite_r12 = true; > + break; > + case PTRACE_EVENTMSG_SYSCALL_EXIT: > + r12 = PTRACE_SYSCALL_EXIT; > + overwrite_r12 = true; > + break; > + default: > + overwrite_r12 = false; > + break; > + } > + > + while (to.left) { > + compat_ulong_t val; > + > + if (!overwrite_r12 || i != 12) > + val = compat_get_user_reg(target, i++); > + else > + val = r12; > + membuf_store(&to, val); > + } > + Can this be condensed too, say by introducing a wrapper for compat_get_user_reg() that does the fudging on r12? [...] Cheers ---Dave