Path: csiph.com!aioe.org!bofh.it!news.nic.it!robomod From: Andy Lutomirski Newsgroups: linux.kernel Subject: Re: [PATCH v3 2/3] x86/ldt: Make modify_ldt optional Date: Fri, 24 Jul 2015 01:50:01 +0200 Message-ID: References: X-Original-To: Kees Cook X-Google-Dkim-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:in-reply-to:references:from:date :message-id:subject:to:cc:content-type; bh=0qRz6vWiQa6UoN6Ez7cEuCcJ8HPOjH6xK9ZG5vRg+ls=; b=UQ7RwcorhA9PaBNpyKt6wVrXd/PWD/rpzpVaXtpMbKeOeUjcVpeApMK8gdj8DLIhLN pHpR0DcPvC1LOkUdxm2nMgpP9aOWvWQ1qGr8poLaLWqrmgHQhMcCM9BcqHDW/4vG1zGA CWPw8ydJEzvg5ktlcApS7z6qvRvaI+1P/CanWi55FoBVgibB0H3dnNu4C6mhGTqbinrb nl+dykRj1qPU9lEHdwIdeJ1XRMFfSQo003y1EkujXbBk3sx4oJ2fIxz4Dh03io8zNBZN Qa/xbxTG6ycDmSHHnUhVEvVSXWUxyd1PpZ31mALVd9VcDSEN5Wmv3a2DasLFCOCb6A3K PFcA== X-Gm-Message-State: ALoCoQkwaCS++hakLW4CRBkf3M9esZwWxpk9qmRB3XA7/A8BihFBz/D7gQZydN+R7lIaLvb/nsZd X-Received: by 10.152.1.66 with SMTP id 2mr10830337lak.56.1437694833994; Thu, 23 Jul 2015 16:40:33 -0700 (PDT) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 63 Organization: linux.* mail to news gateway X-Original-Cc: Willy Tarreau , Andy Lutomirski , Peter Zijlstra , Steven Rostedt , "security@kernel.org" , X86 ML , Borislav Petkov , Sasha Levin , LKML , Konrad Rzeszutek Wilk , Boris Ostrovsky , Andrew Cooper , Jan Beulich , xen-devel X-Original-Date: Thu, 23 Jul 2015 16:40:14 -0700 X-Original-Message-ID: X-Original-References: <7bfde005b84a90a83bf668a320c7d4ad1b940065.1437592883.git.luto@kernel.org> <20150723102434.GA2929@1wt.eu> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: aioe.org linux.kernel:1191406 On Thu, Jul 23, 2015 at 4:36 PM, Kees Cook wrote: > On Thu, Jul 23, 2015 at 3:24 AM, Willy Tarreau wrote: >> #ifdef CONFIG_SMP >> static void flush_ldt(void *current_mm) >> { >> @@ -254,6 +260,9 @@ asmlinkage int sys_modify_ldt(int func, void __user *ptr, >> { >> int ret = -ENOSYS; >> >> + if (!sysctl_modify_ldt) >> + return ret; >> + >> switch (func) { >> case 0: >> ret = read_ldt(ptr, bytecount); >> diff --git a/kernel/sysctl.c b/kernel/sysctl.c >> index 2082b1a..60270c6 100644 >> --- a/kernel/sysctl.c >> +++ b/kernel/sysctl.c >> @@ -111,6 +111,9 @@ extern int sysctl_nr_open_min, sysctl_nr_open_max; >> #ifndef CONFIG_MMU >> extern int sysctl_nr_trim_pages; >> #endif >> +#ifdef CONFIG_X86 >> +extern int sysctl_modify_ldt; >> +#endif >> >> /* Constants used for minimum and maximum */ >> #ifdef CONFIG_LOCKUP_DETECTOR >> @@ -962,6 +965,13 @@ static struct ctl_table kern_table[] = { >> .mode = 0644, >> .proc_handler = proc_dointvec, >> }, >> + { >> + .procname = "modify_ldt", >> + .data = &sysctl_modify_ldt, >> + .maxlen = sizeof(int), >> + .mode = 0644, >> + .proc_handler = proc_dointvec, >> + }, >> #endif >> #if defined(CONFIG_MMU) >> { > > I've been pondering something like this that is even MORE generic, for > any syscall. Something like a "syscalls" directory under > /proc/sys/kernel, with 1 entry per syscall. "0" is "available", "1" is > disabled, and "-1" disabled until next boot. > It might want to be /proc/sys/kernel/syscalls/[abi]/[name], possibly with more than just those options. We might want "disabled, returns ENOSYS", "disabled, returns EPERM", and a lock bit. On x86 at least, the implementation's easy -- we can just poke the syscall table. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/