From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Howells Subject: [PATCH 5/5] Add a sysrq option to exit secure boot mode Date: Wed, 24 May 2017 15:46:03 +0100 Message-ID: <149563716341.9419.12043461651917925181.stgit@warthog.procyon.org.uk> References: <149563711758.9419.11406612723056598045.stgit@warthog.procyon.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <149563711758.9419.11406612723056598045.stgit@warthog.procyon.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: ard.biesheuvel@linaro.org Cc: dhowells@redhat.com, matthew.garrett@nebula.com, linux-security-module@vger.kernel.org, linux-efi@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-efi@vger.kernel.org From: Kyle McMartin Make sysrq+x exit secure boot mode on x86_64, thereby allowing the running kernel image to be modified. This lifts the lockdown. Signed-off-by: Kyle McMartin Signed-off-by: David Howells cc: x86@kernel.org --- arch/x86/include/asm/efi.h | 2 ++ drivers/firmware/efi/Kconfig | 10 ++++++++++ drivers/firmware/efi/secureboot.c | 37 +++++++++++++++++++++++++++++++++++++ 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 +- 8 files changed, 76 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h index 6d74cc3802e6..b4e641ace1bd 100644 --- a/arch/x86/include/asm/efi.h +++ b/arch/x86/include/asm/efi.h @@ -31,6 +31,8 @@ #define ARCH_EFI_IRQ_FLAGS_MASK X86_EFLAGS_IF +#define EFI_SECURE_BOOT_EXIT_KEY 'x' + #ifdef CONFIG_X86_32 extern unsigned long asmlinkage efi_call_phys(void *, ...); diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig index d03af2d5f52f..bd27f35ba528 100644 --- a/drivers/firmware/efi/Kconfig +++ b/drivers/firmware/efi/Kconfig @@ -108,6 +108,16 @@ config EFI_SECURE_BOOT - Loading unsigned modules - Kexec'ing unsigned images +config EFI_ALLOW_SECURE_BOOT_EXIT + def_bool n + depends on EFI_SECURE_BOOT && MAGIC_SYSRQ + select ALLOW_LOCKDOWN_LIFT + prompt "Allow secure boot mode to be exited with SysRq+x on a keyboard" + ---help--- + Allow secure boot mode to be exited and the kernel lockdown lifted by + typing SysRq+x on a keyboard attached to the system (not permitted + through procfs). + config EFI_ARMSTUB bool diff --git a/drivers/firmware/efi/secureboot.c b/drivers/firmware/efi/secureboot.c index 7292a3b832e3..be624a16996e 100644 --- a/drivers/firmware/efi/secureboot.c +++ b/drivers/firmware/efi/secureboot.c @@ -13,6 +13,8 @@ #include #include #include +#include +#include /* * Decide what to do when UEFI secure boot mode is enabled. @@ -41,3 +43,38 @@ void __init efi_set_secure_boot(enum efi_secureboot_mode mode) } } } + +/* + * Allow secure boot to be lifted by pressing something like SysRq+x (and not + * by echoing the appropriate letter into the sysrq-trigger file). + */ +#ifdef CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT + +static void sysrq_handle_secure_boot(int key) +{ + if (!efi_enabled(EFI_SECURE_BOOT)) + return; + + pr_info("Secure boot disabled\n"); + lift_kernel_lockdown(); +} + +static struct sysrq_key_op secure_boot_sysrq_op = { + .handler = sysrq_handle_secure_boot, + .help_msg = "unSB(x)", + .action_msg = "Disabling Secure Boot restrictions", + .enable_mask = SYSRQ_DISABLE_USERSPACE, +}; + +static int __init efi_secure_boot_sysrq(void) +{ + if (efi_enabled(EFI_SECURE_BOOT)) { + secure_boot_sysrq_op.help_msg[5] = EFI_SECURE_BOOT_EXIT_KEY; + register_sysrq_key(EFI_SECURE_BOOT_EXIT_KEY, &secure_boot_sysrq_op); + } + return 0; +} + +late_initcall(efi_secure_boot_sysrq); + +#endif /* CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT */ diff --git a/drivers/input/misc/uinput.c b/drivers/input/misc/uinput.c index 022be0e22eba..4a054a564636 100644 --- a/drivers/input/misc/uinput.c +++ b/drivers/input/misc/uinput.c @@ -387,6 +387,7 @@ static int uinput_allocate_device(struct uinput_device *udev) if (!udev->dev) return -ENOMEM; + udev->dev->flags |= INPUTDEV_FLAGS_SYNTHETIC; udev->dev->event = uinput_dev_event; input_set_drvdata(udev->dev, udev); diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 3ffc1ce29023..8b766dbad6dd 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -481,6 +481,7 @@ 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 */ @@ -524,7 +525,7 @@ 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; @@ -544,11 +545,15 @@ 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); @@ -580,7 +585,7 @@ 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); @@ -661,7 +666,7 @@ static void sysrq_do_reset(unsigned long _state) 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; } @@ -1097,7 +1104,7 @@ 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 a65e3b24fb18..8b0357175049 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 387fa7d05c98..f7c52a9ea394 100644 --- a/include/linux/sysrq.h +++ b/include/linux/sysrq.h @@ -28,6 +28,8 @@ #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; @@ -42,8 +44,12 @@ 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 c8146d53ca67..b480cadf9272 100644 --- a/kernel/debug/kdb/kdb_main.c +++ b/kernel/debug/kdb/kdb_main.c @@ -1970,7 +1970,7 @@ 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;