[02/27] Add a SysRq option to lift kernel lockdown

Message ID	20190228231203.212359-2-matthewgarrett@google.com (mailing list archive)
State	New, archived
Headers	show Return-Path: <linux-security-module-owner@kernel.org> Date: Thu, 28 Feb 2019 15:11:38 -0800 In-Reply-To: <20190228231203.212359-1-matthewgarrett@google.com> Message-Id: <20190228231203.212359-2-matthewgarrett@google.com> Mime-Version: 1.0 References: <CACdnJuvW47m3JvEcuEX1bsr+L2Ht9LDn_iCuPbHLOoaohOFW4Q@mail.gmail.com> <20190228231203.212359-1-matthewgarrett@google.com> Subject: [PATCH 02/27] Add a SysRq option to lift kernel lockdown From: Matthew Garrett <matthewgarrett@google.com> To: jmorris@namei.org Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, dhowells@redhat.com Content-Type: text/plain; charset="UTF-8" Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk
Series	[PULL,REQUEST] Lock down patches \| expand [PULL,REQUEST] Lock down patches [02/27] Add a SysRq option to lift kernel lockdown [03/27] Enforce module signatures if the kernel is locked down [04/27] Restrict /dev/{mem,kmem,port} when the kernel is locked down [05/27] kexec_load: Disable at runtime if the kernel is locked down [06/27] Copy secure_boot flag in boot params across kexec reboot [07/27] kexec_file: split KEXEC_VERIFY_SIG into KEXEC_SIG and KEXEC_SIG_FORCE [08/27] kexec_file: Restrict at runtime if the kernel is locked down [09/27] hibernate: Disable when the kernel is locked down [10/27] uswsusp: Disable when the kernel is locked down [11/27] PCI: Lock down BAR access when the kernel is locked down [12/27] x86: Lock down IO port access when the kernel is locked down [13/27] x86/msr: Restrict MSR access when the kernel is locked down [14/27] ACPI: Limit access to custom_method when the kernel is locked down [15/27] acpi: Ignore acpi_rsdp kernel param when the kernel has been locked down [16/27] acpi: Disable ACPI table override if the kernel is locked down [17/27] acpi: Disable APEI error injection if the kernel is locked down [18/27] Prohibit PCMCIA CIS storage when the kernel is locked down [19/27] Lock down TIOCSSERIAL [20/27] Lock down module params that specify hardware parameters (eg. ioport) [21/27] x86/mmiotrace: Lock down the testmmiotrace module [22/27] Lock down /proc/kcore [23/27] Lock down kprobes [24/27] bpf: Restrict kernel image access functions when the kernel is locked down [25/27] Lock down perf [26/27] debugfs: Restrict debugfs when the kernel is locked down [27/27] lockdown: Print current->comm in restriction messages

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 <linux/linkage.h> #include <asm/page_types.h> +#define LOCKDOWN_LIFT_KEY 'x' + #ifdef __i386__ #include <linux/pfn.h> diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c index 26ec603fe220..a73e92490286 100644 --- a/drivers/input/misc/uinput.c +++ b/drivers/input/misc/uinput.c @@ -366,6 +366,7 @@ 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 c2aff0006de2..afaf6fa17c9a 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -245,6 +245,15 @@ 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 <linux/security.h> #include <linux/export.h> +#include <linux/sysrq.h> +#include <asm/setup.h> +#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 */

[02/27] Add a SysRq option to lift kernel lockdown

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Patch