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    Subject[PATCH 06/24] Add a sysrq option to exit secure boot mode
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    Date
    From: Kyle McMartin <kyle@redhat.com>

    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 <kyle@redhat.com>
    Signed-off-by: David Howells <dhowells@redhat.com>
    cc: x86@kernel.org
    ---

    arch/x86/Kconfig | 10 ++++++++++
    arch/x86/kernel/setup.c | 31 +++++++++++++++++++++++++++++++
    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 +-
    7 files changed, 68 insertions(+), 8 deletions(-)

    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 21f39855661d..457c04971849 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -1829,6 +1829,16 @@ config EFI_SECURE_BOOT_LOCK_DOWN
    image. Say Y here to automatically lock down the kernel when a
    system boots with UEFI Secure Boot enabled.

    +config EFI_ALLOW_SECURE_BOOT_EXIT
    + def_bool n
    + depends on EFI_SECURE_BOOT_LOCK_DOWN && 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 SECCOMP
    def_bool y
    prompt "Enable seccomp to safely compute untrusted bytecode"
    diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c
    index 85dfa745c442..a415a4817684 100644
    --- a/arch/x86/kernel/setup.c
    +++ b/arch/x86/kernel/setup.c
    @@ -71,6 +71,11 @@
    #include <linux/jiffies.h>
    #include <linux/security.h>

    +#include <linux/fips.h>
    +#include <linux/cred.h>
    +#include <linux/sysrq.h>
    +#include <linux/init_task.h>
    +
    #include <video/edid.h>

    #include <asm/mtrr.h>
    @@ -1330,6 +1335,32 @@ void __init i386_reserve_resources(void)

    #endif /* CONFIG_X86_32 */

    +#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 secure_boot_sysrq(void)
    +{
    + if (efi_enabled(EFI_SECURE_BOOT))
    + register_sysrq_key('x', &secure_boot_sysrq_op);
    + return 0;
    +}
    +late_initcall(secure_boot_sysrq);
    +#endif /*CONFIG_EFI_ALLOW_SECURE_BOOT_EXIT*/
    +
    +
    static struct notifier_block kernel_offset_notifier = {
    .notifier_call = dump_kernel_offset
    };
    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 c6fc7141d7b2..0c96cf60f1a6 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;
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