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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 38B44C38159 for ; Wed, 18 Jan 2023 20:41:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230042AbjARUlE (ORCPT ); Wed, 18 Jan 2023 15:41:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47552 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229537AbjARUlB (ORCPT ); Wed, 18 Jan 2023 15:41:01 -0500 Received: from desiato.infradead.org (desiato.infradead.org [IPv6:2001:8b0:10b:1:d65d:64ff:fe57:4e05]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B76CD4A202; Wed, 18 Jan 2023 12:40:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=md4uxanlxoNCe8b7gZ4uQll2YVbv50mEZqFSNP3ZnLU=; b=ILnzoL+FrViTUNFXn7/4Gknk1C Hq3IMtMMl24o/v4Rk232I9bNeFJ8Vy0p0oF387AqCU8GVxQR9wkPOUH7oZ4PAFsk1YvfXRs3NFpqF cr3w+1BNURAhHpGsoZmlnj/LoKnn5jy2n7aryqPFSVRzRBbnOyvTmxBerMZqvmAcNlbu9g1WfWnHE NeUiWw2n5QyW3cReWUPgFLVbLLdx8tqHbCkomzUvpJVvUmLVUf65FeaXkUzuLyFP5NuUvGUG7fCZ1 +P8Ic49FpE3HdcMkaBW6oEbh75zvK8Zm+SiBgomFNP8VrOderQ4P57tgzm5XjBwpLp/F1qMWS93Oh u4aPJMtA==; Received: from j130084.upc-j.chello.nl ([24.132.130.84] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.96 #2 (Red Hat Linux)) id 1pIFE7-00067h-1t; Wed, 18 Jan 2023 20:40:09 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4B06A300094; Wed, 18 Jan 2023 21:40:33 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 0C87823BD9D65; Wed, 18 Jan 2023 21:40:33 +0100 (CET) Date: Wed, 18 Jan 2023 21:40:32 +0100 From: Peter Zijlstra To: Gregory Price Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, krisman@collabora.com, tglx@linutronix.de, luto@kernel.org, oleg@redhat.com, ebiederm@xmission.com, akpm@linux-foundation.org, adobriyan@gmail.com, corbet@lwn.net, shuah@kernel.org Subject: Re: [PATCH 1/3] ptrace,syscall_user_dispatch: Implement Syscall User Dispatch Suspension Message-ID: References: <20230109153348.5625-1-gregory.price@memverge.com> <20230109153348.5625-2-gregory.price@memverge.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org On Wed, Jan 18, 2023 at 02:49:31PM -0500, Gregory Price wrote: > On Wed, Jan 18, 2023 at 02:41:00PM -0500, Gregory Price wrote: > > ---------- Forwarded message --------- > > From: Peter Zijlstra > > Date: Wed, Jan 18, 2023 at 12:16 PM > > Subject: Re: [PATCH 1/3] ptrace,syscall_user_dispatch: Implement Syscall > > User Dispatch Suspension > > To: Gregory Price > > > > > > On Mon, Jan 09, 2023 at 10:33:46AM -0500, Gregory Price wrote: > > > @@ -36,6 +37,10 @@ bool syscall_user_dispatch(struct pt_regs *regs) > > > struct syscall_user_dispatch *sd = ¤t->syscall_dispatch; > > > char state; > > > > > > + if (IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) && > > > + unlikely(current->ptrace & > > PT_SUSPEND_SYSCALL_USER_DISPATCH)) > > > + return false; > > > + > > > if (likely(instruction_pointer(regs) - sd->offset < sd->len)) > > > return false; > > > > > > > So by making syscall_user_dispatch() return false, we'll make > > syscall_trace_enter() continue to handle things, and supposedly you want > > to land in ptrace_report_syscall_entry(), right? > > > > ... snip ... > > > > Should setting this then not also depend on having > > SYSCALL_WORK_SYSCALL_TRACE set? Because without that, you get 'funny' > > things. > > Hm, this is an interesting question. My thoughts are that I want the > process to handle the syscall as-if syscall user dispatch was not > present at all, regardless of SYSCALL_TRACE. > > This is because some software, like CRIU, actually injects syscalls to > run in the context of the software in an effort to collect resources. Oh, right. I used to know that. > So I actually *want* those 'funny' things to occur, because they're most > likely intentional. I don't necessarily want to intercept system calls > that subsequently occur (although i might). > > So if this feature required SYSCALL_TRACE, you would no longer be able > to inject system calls ala CRIU. Yeah, I suppose you're right. It makes it a very sharp instrument, but I suppose you get what you asked for.