From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Sistare Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC Date: Thu, 30 Jul 2020 14:27:21 -0400 Message-ID: References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <20200730152250.GG23808@casper.infradead.org> <20200730171251.GI23808@casper.infradead.org> <63a7404c-e4f6-a82e-257b-217585b0277f@oracle.com> <20200730174956.GK23808@casper.infradead.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from userp2130.oracle.com ([156.151.31.86]:36808 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726343AbgG3S2H (ORCPT ); Thu, 30 Jul 2020 14:28:07 -0400 In-Reply-To: <20200730174956.GK23808@casper.infradead.org> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org List-ID: To: Matthew Wilcox Cc: Anthony Yznaga , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, gerg@linux-m68k.org, ktkhai@virtuozzo.com, christian.brauner@ubuntu.com, peterz@infradead.org, esyr@redhat.com, jgg@ziepe.ca, christian@kellner.me, areber@redhat.com, cyphar@cyphar.com On 7/30/2020 1:49 PM, Matthew Wilcox wrote: > On Thu, Jul 30, 2020 at 01:35:51PM -0400, Steven Sistare wrote: >> mshare + VA reservation is another possible solution. >> >> Or MADV_DOEXEC alone, which is ready now. I hope we can get back to reviewing that. > > We are. This is the part of the review process where we explore other > solutions to the problem. > >>>> Also, we need to support updating legacy processes that already created anon segments. >>>> We inject code that calls MADV_DOEXEC for such segments. >>> >>> Yes, I was assuming you'd inject code that called mshare(). >> >> OK, mshare works on existing memory and builds a new vma. > > Actually, reparents an existing VMA, and reuses the existing page tables. > >>> Actually, since you're injecting code, why do you need the kernel to >>> be involved? You can mmap the new executable and any libraries it depends >>> upon, set up a new stack and jump to the main() entry point, all without >>> calling exec(). I appreciate it'd be a fair amount of code, but it'd all >>> be in userspace and you can probably steal / reuse code from ld.so (I'm >>> not familiar with the details of how setting up an executable is done). >> >> Duplicating all the work that the kernel and loader do to exec a process would >> be error prone, require ongoing maintenance, and be redundant. Better to define >> a small kernel extension and leave exec to the kernel. > > Either this is a one-off kind of thing, in which case it doesn't need > ongoing maintenance, or it's something with broad applicability, in > which case it can live as its own userspace project. It could even > start off life as part of qemu and then fork into its own project. exec will be enhanced over time in the kernel. A separate user space implementation would need to track that. Reimplementing exec in userland would be a big gross mess. Not a good solution when we have simple and concise ways of solving the problem. > The idea of tagging an ELF executable to say "I can cope with having > chunks of my address space provided to me by my executor" is ... odd. I don't disagree. But it is useful. We already pass a block of data containing environment variables and arguments from one process to the next. Preserving additional segments is not a big leap from there. - Steve From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [RFC PATCH 0/5] madvise MADV_DOEXEC References: <1595869887-23307-1-git-send-email-anthony.yznaga@oracle.com> <20200730152250.GG23808@casper.infradead.org> <20200730171251.GI23808@casper.infradead.org> <63a7404c-e4f6-a82e-257b-217585b0277f@oracle.com> <20200730174956.GK23808@casper.infradead.org> From: Steven Sistare Message-ID: Date: Thu, 30 Jul 2020 14:27:21 -0400 MIME-Version: 1.0 In-Reply-To: <20200730174956.GK23808@casper.infradead.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Matthew Wilcox Cc: Anthony Yznaga , linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-arch@vger.kernel.org, mhocko@kernel.org, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, arnd@arndb.de, ebiederm@xmission.com, keescook@chromium.org, gerg@linux-m68k.org, ktkhai@virtuozzo.com, christian.brauner@ubuntu.com, peterz@infradead.org, esyr@redhat.com, jgg@ziepe.ca, christian@kellner.me, areber@redhat.com, cyphar@cyphar.com List-ID: Message-ID: <20200730182721.i8eg8NGn5Es9748C_odBI7OFpY6uK8XQnLoblrincd4@z> On 7/30/2020 1:49 PM, Matthew Wilcox wrote: > On Thu, Jul 30, 2020 at 01:35:51PM -0400, Steven Sistare wrote: >> mshare + VA reservation is another possible solution. >> >> Or MADV_DOEXEC alone, which is ready now. I hope we can get back to reviewing that. > > We are. This is the part of the review process where we explore other > solutions to the problem. > >>>> Also, we need to support updating legacy processes that already created anon segments. >>>> We inject code that calls MADV_DOEXEC for such segments. >>> >>> Yes, I was assuming you'd inject code that called mshare(). >> >> OK, mshare works on existing memory and builds a new vma. > > Actually, reparents an existing VMA, and reuses the existing page tables. > >>> Actually, since you're injecting code, why do you need the kernel to >>> be involved? You can mmap the new executable and any libraries it depends >>> upon, set up a new stack and jump to the main() entry point, all without >>> calling exec(). I appreciate it'd be a fair amount of code, but it'd all >>> be in userspace and you can probably steal / reuse code from ld.so (I'm >>> not familiar with the details of how setting up an executable is done). >> >> Duplicating all the work that the kernel and loader do to exec a process would >> be error prone, require ongoing maintenance, and be redundant. Better to define >> a small kernel extension and leave exec to the kernel. > > Either this is a one-off kind of thing, in which case it doesn't need > ongoing maintenance, or it's something with broad applicability, in > which case it can live as its own userspace project. It could even > start off life as part of qemu and then fork into its own project. exec will be enhanced over time in the kernel. A separate user space implementation would need to track that. Reimplementing exec in userland would be a big gross mess. Not a good solution when we have simple and concise ways of solving the problem. > The idea of tagging an ELF executable to say "I can cope with having > chunks of my address space provided to me by my executor" is ... odd. I don't disagree. But it is useful. We already pass a block of data containing environment variables and arguments from one process to the next. Preserving additional segments is not a big leap from there. - Steve