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[209.132.180.67]) by mx.google.com with ESMTP id k127si2689716pgc.124.2019.03.06.16.10.38; Wed, 06 Mar 2019 16:10:53 -0800 (PST) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; dkim=fail header.i=@infradead.org header.s=merlin.20170209 header.b=cx1XnzMu; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726305AbfCGAKD (ORCPT + 99 others); Wed, 6 Mar 2019 19:10:03 -0500 Received: from merlin.infradead.org ([205.233.59.134]:48050 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbfCGAKC (ORCPT ); Wed, 6 Mar 2019 19:10:02 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=Content-Transfer-Encoding:Content-Type: In-Reply-To:MIME-Version:Date:Message-ID:From:References:Cc:To:Subject:Sender :Reply-To:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=4E7bIP906TTs+lIVBBIVfIWGrDCB7F6wktJATD0xrQQ=; b=cx1XnzMuGJ3QVshgD6hd0X2reQ hqqtwzTr+hkT25DIUfn37EHXbxnxCyqKVLsS8vUYHuAQvRgAKeFw0TO8qeKwwsvEcqJRn+AnSCt8O QMlmT2P/7xrBchnDiUPa81WL70sB7OAWoI1liV/r2aNH+WQz1AyVhLQBHrBOtAjaRAa3Mxel7hFIv NGm0BbRudGt8E1RRQjPCw28hkWxo62o/kt6Jnpf5vh4+R9eZrnQ8YDul7ZC7WzpjTbshxpEmF8XVR AzdTY437vUaxrF7LysBJ0ocEHPR74/XAwcc29jqIQ69EkdEqFP3JLnRutIUi9njHSOL5RXK/m2FwG qI0Hun2g==; Received: from static-50-53-52-16.bvtn.or.frontiernet.net ([50.53.52.16] helo=dragon.dunlab) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1h1gbn-0007Ci-Ht; Thu, 07 Mar 2019 00:10:00 +0000 Subject: Re: [PATCH 02/27] Add a SysRq option to lift kernel lockdown To: Matthew Garrett , jmorris@namei.org Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dhowells@redhat.com References: <20190306235913.6631-1-matthewgarrett@google.com> <20190306235913.6631-3-matthewgarrett@google.com> From: Randy Dunlap Message-ID: <7bcd6149-332d-15f8-31e1-ef0a6b7f496e@infradead.org> Date: Wed, 6 Mar 2019 16:09:57 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.3.0 MIME-Version: 1.0 In-Reply-To: <20190306235913.6631-3-matthewgarrett@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/6/19 3:58 PM, Matthew Garrett wrote: > From: Kyle McMartin > > Make an option to provide a sysrq key that will lift the kernel lockdown, > thereby allowing the running kernel image to be accessed and modified. You still need to document this in Documentation/admin-guide/sysrq.rst, like I mentioned last week. > On x86 this is triggered with SysRq+x, but this key may not be available on > all arches, so it is set by setting LOCKDOWN_LIFT_KEY in asm/setup.h. > Since this macro must be defined in an arch to be able to use this facility > for that arch, the Kconfig option is restricted to arches that support it. > > Signed-off-by: Kyle McMartin > Signed-off-by: David Howells > cc: x86@kernel.org > Signed-off-by: Matthew Garrett > --- > arch/x86/include/asm/setup.h | 2 ++ > drivers/input/misc/uinput.c | 1 + > drivers/tty/sysrq.c | 19 ++++++++++----- > include/linux/input.h | 5 ++++ > include/linux/sysrq.h | 8 +++++- > kernel/debug/kdb/kdb_main.c | 2 +- > security/Kconfig | 9 +++++++ > security/lock_down.c | 47 ++++++++++++++++++++++++++++++++++++ > 8 files changed, 85 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h > index ed8ec011a9fd..8daf633a5347 100644 > --- a/arch/x86/include/asm/setup.h > +++ b/arch/x86/include/asm/setup.h > @@ -9,6 +9,8 @@ > #include > #include > > +#define LOCKDOWN_LIFT_KEY 'x' > + > #ifdef __i386__ > > #include > diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c > index 8ec483e8688b..c2a77dc73fa0 100644 > --- a/drivers/input/misc/uinput.c > +++ b/drivers/input/misc/uinput.c > @@ -365,6 +365,7 @@ static int uinput_create_device(struct uinput_device *udev) > dev->flush = uinput_dev_flush; > } > > + dev->flags |= INPUTDEV_FLAGS_SYNTHETIC; > dev->event = uinput_dev_event; > > input_set_drvdata(udev->dev, udev); > diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c > index 1f03078ec352..0a05d336008e 100644 > --- a/drivers/tty/sysrq.c > +++ b/drivers/tty/sysrq.c > @@ -480,6 +480,7 @@ static struct sysrq_key_op *sysrq_key_table[36] = { > /* x: May be registered on mips for TLB dump */ > /* x: May be registered on ppc/powerpc for xmon */ > /* x: May be registered on sparc64 for global PMU dump */ > + /* x: May be registered on x86_64 for disabling secure boot */ > NULL, /* x */ > /* y: May be registered on sparc64 for global register dump */ > NULL, /* y */ > @@ -523,7 +524,7 @@ static void __sysrq_put_key_op(int key, struct sysrq_key_op *op_p) > sysrq_key_table[i] = op_p; > } > > -void __handle_sysrq(int key, bool check_mask) > +void __handle_sysrq(int key, unsigned int from) > { > struct sysrq_key_op *op_p; > int orig_log_level; > @@ -543,11 +544,15 @@ void __handle_sysrq(int key, bool check_mask) > > op_p = __sysrq_get_key_op(key); > if (op_p) { > + /* Ban synthetic events from some sysrq functionality */ > + if ((from == SYSRQ_FROM_PROC || from == SYSRQ_FROM_SYNTHETIC) && > + op_p->enable_mask & SYSRQ_DISABLE_USERSPACE) > + printk("This sysrq operation is disabled from userspace.\n"); > /* > * Should we check for enabled operations (/proc/sysrq-trigger > * should not) and is the invoked operation enabled? > */ > - if (!check_mask || sysrq_on_mask(op_p->enable_mask)) { > + if (from == SYSRQ_FROM_KERNEL || sysrq_on_mask(op_p->enable_mask)) { > pr_cont("%s\n", op_p->action_msg); > console_loglevel = orig_log_level; > op_p->handler(key); > @@ -579,7 +584,7 @@ void __handle_sysrq(int key, bool check_mask) > void handle_sysrq(int key) > { > if (sysrq_on()) > - __handle_sysrq(key, true); > + __handle_sysrq(key, SYSRQ_FROM_KERNEL); > } > EXPORT_SYMBOL(handle_sysrq); > > @@ -659,7 +664,7 @@ static void sysrq_do_reset(struct timer_list *t) > static void sysrq_handle_reset_request(struct sysrq_state *state) > { > if (state->reset_requested) > - __handle_sysrq(sysrq_xlate[KEY_B], false); > + __handle_sysrq(sysrq_xlate[KEY_B], SYSRQ_FROM_KERNEL); > > if (sysrq_reset_downtime_ms) > mod_timer(&state->keyreset_timer, > @@ -812,8 +817,10 @@ static bool sysrq_handle_keypress(struct sysrq_state *sysrq, > > default: > if (sysrq->active && value && value != 2) { > + int from = sysrq->handle.dev->flags & INPUTDEV_FLAGS_SYNTHETIC ? > + SYSRQ_FROM_SYNTHETIC : 0; > sysrq->need_reinject = false; > - __handle_sysrq(sysrq_xlate[code], true); > + __handle_sysrq(sysrq_xlate[code], from); > } > break; > } > @@ -1096,7 +1103,7 @@ static ssize_t write_sysrq_trigger(struct file *file, const char __user *buf, > > if (get_user(c, buf)) > return -EFAULT; > - __handle_sysrq(c, false); > + __handle_sysrq(c, SYSRQ_FROM_PROC); > } > > return count; > diff --git a/include/linux/input.h b/include/linux/input.h > index 7c7516eb7d76..38cd0ea72c37 100644 > --- a/include/linux/input.h > +++ b/include/linux/input.h > @@ -42,6 +42,7 @@ struct input_value { > * @phys: physical path to the device in the system hierarchy > * @uniq: unique identification code for the device (if device has it) > * @id: id of the device (struct input_id) > + * @flags: input device flags (SYNTHETIC, etc.) > * @propbit: bitmap of device properties and quirks > * @evbit: bitmap of types of events supported by the device (EV_KEY, > * EV_REL, etc.) > @@ -124,6 +125,8 @@ struct input_dev { > const char *uniq; > struct input_id id; > > + unsigned int flags; > + > unsigned long propbit[BITS_TO_LONGS(INPUT_PROP_CNT)]; > > unsigned long evbit[BITS_TO_LONGS(EV_CNT)]; > @@ -190,6 +193,8 @@ struct input_dev { > }; > #define to_input_dev(d) container_of(d, struct input_dev, dev) > > +#define INPUTDEV_FLAGS_SYNTHETIC 0x000000001 > + > /* > * Verify that we are in sync with input_device_id mod_devicetable.h #defines > */ > diff --git a/include/linux/sysrq.h b/include/linux/sysrq.h > index 8c71874e8485..7de1f08b60a9 100644 > --- a/include/linux/sysrq.h > +++ b/include/linux/sysrq.h > @@ -29,6 +29,8 @@ > #define SYSRQ_ENABLE_BOOT 0x0080 > #define SYSRQ_ENABLE_RTNICE 0x0100 > > +#define SYSRQ_DISABLE_USERSPACE 0x00010000 > + > struct sysrq_key_op { > void (*handler)(int); > char *help_msg; > @@ -43,8 +45,12 @@ struct sysrq_key_op { > * are available -- else NULL's). > */ > > +#define SYSRQ_FROM_KERNEL 0x0001 > +#define SYSRQ_FROM_PROC 0x0002 > +#define SYSRQ_FROM_SYNTHETIC 0x0004 > + > void handle_sysrq(int key); > -void __handle_sysrq(int key, bool check_mask); > +void __handle_sysrq(int key, unsigned int from); > int register_sysrq_key(int key, struct sysrq_key_op *op); > int unregister_sysrq_key(int key, struct sysrq_key_op *op); > struct sysrq_key_op *__sysrq_get_key_op(int key); > diff --git a/kernel/debug/kdb/kdb_main.c b/kernel/debug/kdb/kdb_main.c > index 82a3b32a7cfc..efee1abf5e8e 100644 > --- a/kernel/debug/kdb/kdb_main.c > +++ b/kernel/debug/kdb/kdb_main.c > @@ -1981,7 +1981,7 @@ static int kdb_sr(int argc, const char **argv) > return KDB_ARGCOUNT; > > kdb_trap_printk++; > - __handle_sysrq(*argv[1], check_mask); > + __handle_sysrq(*argv[1], check_mask ? SYSRQ_FROM_KERNEL : 0); > kdb_trap_printk--; > > return 0; > diff --git a/security/Kconfig b/security/Kconfig > index 47dc3403b5af..8346eb883336 100644 > --- a/security/Kconfig > +++ b/security/Kconfig > @@ -244,6 +244,15 @@ config LOCK_DOWN_KERNEL_FORCE > help > Enable the kernel lock down functionality automatically at boot. > > +config ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > + bool "Allow the kernel lockdown to be lifted by SysRq" > + depends on LOCK_DOWN_KERNEL > + depends on MAGIC_SYSRQ > + depends on X86 > + help > + Allow the lockdown on a kernel to be lifted, by pressing a SysRq key > + combination on a wired keyboard. > + > source "security/selinux/Kconfig" > source "security/smack/Kconfig" > source "security/tomoyo/Kconfig" > diff --git a/security/lock_down.c b/security/lock_down.c > index 13a8228c1034..cfbc2c39712b 100644 > --- a/security/lock_down.c > +++ b/security/lock_down.c > @@ -11,8 +11,14 @@ > > #include > #include > +#include > +#include > > +#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > +static __read_mostly bool kernel_locked_down; > +#else > static __ro_after_init bool kernel_locked_down; > +#endif > > /* > * Put the kernel into lock-down mode. > @@ -57,3 +63,44 @@ bool __kernel_is_locked_down(const char *what, bool first) > return kernel_locked_down; > } > EXPORT_SYMBOL(__kernel_is_locked_down); > + > +#ifdef CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ > + > +/* > + * Take the kernel out of lockdown mode. > + */ > +static void lift_kernel_lockdown(void) > +{ > + pr_notice("Lifting lockdown\n"); > + kernel_locked_down = false; > +} > + > +/* > + * Allow lockdown to be lifted by pressing something like SysRq+x (and not by > + * echoing the appropriate letter into the sysrq-trigger file). > + */ > +static void sysrq_handle_lockdown_lift(int key) > +{ > + if (kernel_locked_down) > + lift_kernel_lockdown(); > +} > + > +static struct sysrq_key_op lockdown_lift_sysrq_op = { > + .handler = sysrq_handle_lockdown_lift, > + .help_msg = "unSB(x)", > + .action_msg = "Disabling Secure Boot restrictions", > + .enable_mask = SYSRQ_DISABLE_USERSPACE, > +}; > + > +static int __init lockdown_lift_sysrq(void) > +{ > + if (kernel_locked_down) { > + lockdown_lift_sysrq_op.help_msg[5] = LOCKDOWN_LIFT_KEY; > + register_sysrq_key(LOCKDOWN_LIFT_KEY, &lockdown_lift_sysrq_op); > + } > + return 0; > +} > + > +late_initcall(lockdown_lift_sysrq); > + > +#endif /* CONFIG_ALLOW_LOCKDOWN_LIFT_BY_SYSRQ */ > -- ~Randy