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232 lines
8.8 KiB
232 lines
8.8 KiB
From 8f73052885892bc0dbc01e297f79d7cf4925e491 Mon Sep 17 00:00:00 2001
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From: Javier Martinez Canillas <javierm@redhat.com>
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Date: Mon, 28 Sep 2020 20:08:33 +0200
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Subject: [PATCH] efi: Use grub_is_lockdown() instead of hardcoding a disabled
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modules list
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Now the GRUB can check if it has been locked down and this can be used to
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prevent executing commands that can be utilized to circumvent the UEFI
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Secure Boot mechanisms. So, instead of hardcoding a list of modules that
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have to be disabled, prevent the usage of commands that can be dangerous.
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This not only allows the commands to be disabled on other platforms, but
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also properly separate the concerns. Since the shim_lock verifier logic
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should be only about preventing to run untrusted binaries and not about
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defining these kind of policies.
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Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
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Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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Signed-off-by: Stefan Sørensen <stefan.sorensen@spectralink.com>
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---
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docs/grub.texi | 15 +++++++++------
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grub-core/commands/i386/wrmsr.c | 5 +++--
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grub-core/commands/iorw.c | 19 ++++++++++---------
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grub-core/commands/memrw.c | 19 ++++++++++---------
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grub-core/kern/efi/sb.c | 41 -----------------------------------------
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5 files changed, 32 insertions(+), 67 deletions(-)
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diff --git a/docs/grub.texi b/docs/grub.texi
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index bdbb329..bbe60a4 100644
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--- a/docs/grub.texi
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+++ b/docs/grub.texi
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@@ -5256,6 +5256,9 @@ only applies to the particular cpu/core/thread that runs the command.
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Also, if you specify a reserved or unimplemented MSR address, it will
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cause a general protection exception (which is not currently being handled)
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and the system will reboot.
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+
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+Note: The command is not allowed when lockdown is enforced (@pxref{Lockdown}).
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+ This is done to prevent subverting various security mechanisms.
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@end deffn
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@node xen_hypervisor
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@@ -5752,12 +5755,12 @@ boot and the shim. This functionality is provided by the shim_lock verifier. It
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is built into the @file{core.img} and is registered if the UEFI secure boot is
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enabled.
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-All modules not stored in the @file{core.img} and the ACPI tables for the
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-@command{acpi} command have to be signed, e.g. using PGP. Additionally, the
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-@command{iorw}, the @command{memrw} and the @command{wrmsr} commands are
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-prohibited if the UEFI secure boot is enabled. This is done due to
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-security reasons. All above mentioned requirements are enforced by the
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-shim_lock verifier logic.
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+All GRUB modules not stored in the @file{core.img}, OS kernels, ACPI tables,
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+Device Trees, etc. have to be signed, e.g, using PGP. Additionally, the commands
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+that can be used to subvert the UEFI secure boot mechanism, such as @command{iorw}
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+and @command{memrw} will not be available when the UEFI secure boot is enabled.
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+This is done for security reasons and are enforced by the GRUB Lockdown mechanism
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+(@pxref{Lockdown}).
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@node Measured Boot
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@section Measuring boot components
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diff --git a/grub-core/commands/i386/wrmsr.c b/grub-core/commands/i386/wrmsr.c
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index 9c5e510..56a29c2 100644
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--- a/grub-core/commands/i386/wrmsr.c
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+++ b/grub-core/commands/i386/wrmsr.c
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@@ -24,6 +24,7 @@
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#include <grub/env.h>
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#include <grub/command.h>
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#include <grub/extcmd.h>
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+#include <grub/lockdown.h>
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#include <grub/i18n.h>
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#include <grub/i386/cpuid.h>
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#include <grub/i386/wrmsr.h>
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@@ -83,8 +84,8 @@ grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char
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GRUB_MOD_INIT(wrmsr)
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{
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- cmd_write = grub_register_command ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
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- N_("Write a value to a CPU model specific register."));
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+ cmd_write = grub_register_command_lockdown ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
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+ N_("Write a value to a CPU model specific register."));
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}
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GRUB_MOD_FINI(wrmsr)
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diff --git a/grub-core/commands/iorw.c b/grub-core/commands/iorw.c
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index a0c164e..584baec 100644
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--- a/grub-core/commands/iorw.c
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+++ b/grub-core/commands/iorw.c
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@@ -23,6 +23,7 @@
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#include <grub/env.h>
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#include <grub/cpu/io.h>
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#include <grub/i18n.h>
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+#include <grub/lockdown.h>
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GRUB_MOD_LICENSE ("GPLv3+");
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@@ -131,17 +132,17 @@ GRUB_MOD_INIT(memrw)
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N_("PORT"), N_("Read 32-bit value from PORT."),
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options);
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cmd_write_byte =
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- grub_register_command ("outb", grub_cmd_write,
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- N_("PORT VALUE [MASK]"),
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- N_("Write 8-bit VALUE to PORT."));
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+ grub_register_command_lockdown ("outb", grub_cmd_write,
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+ N_("PORT VALUE [MASK]"),
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+ N_("Write 8-bit VALUE to PORT."));
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cmd_write_word =
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- grub_register_command ("outw", grub_cmd_write,
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- N_("PORT VALUE [MASK]"),
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- N_("Write 16-bit VALUE to PORT."));
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+ grub_register_command_lockdown ("outw", grub_cmd_write,
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+ N_("PORT VALUE [MASK]"),
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+ N_("Write 16-bit VALUE to PORT."));
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cmd_write_dword =
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- grub_register_command ("outl", grub_cmd_write,
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- N_("ADDR VALUE [MASK]"),
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- N_("Write 32-bit VALUE to PORT."));
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+ grub_register_command_lockdown ("outl", grub_cmd_write,
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+ N_("ADDR VALUE [MASK]"),
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+ N_("Write 32-bit VALUE to PORT."));
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}
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GRUB_MOD_FINI(memrw)
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diff --git a/grub-core/commands/memrw.c b/grub-core/commands/memrw.c
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index 98769ea..d401a6d 100644
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--- a/grub-core/commands/memrw.c
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+++ b/grub-core/commands/memrw.c
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@@ -22,6 +22,7 @@
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#include <grub/extcmd.h>
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#include <grub/env.h>
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#include <grub/i18n.h>
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+#include <grub/lockdown.h>
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GRUB_MOD_LICENSE ("GPLv3+");
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@@ -133,17 +134,17 @@ GRUB_MOD_INIT(memrw)
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N_("ADDR"), N_("Read 32-bit value from ADDR."),
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options);
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cmd_write_byte =
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- grub_register_command ("write_byte", grub_cmd_write,
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- N_("ADDR VALUE [MASK]"),
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- N_("Write 8-bit VALUE to ADDR."));
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+ grub_register_command_lockdown ("write_byte", grub_cmd_write,
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+ N_("ADDR VALUE [MASK]"),
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+ N_("Write 8-bit VALUE to ADDR."));
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cmd_write_word =
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- grub_register_command ("write_word", grub_cmd_write,
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- N_("ADDR VALUE [MASK]"),
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- N_("Write 16-bit VALUE to ADDR."));
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+ grub_register_command_lockdown ("write_word", grub_cmd_write,
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+ N_("ADDR VALUE [MASK]"),
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+ N_("Write 16-bit VALUE to ADDR."));
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cmd_write_dword =
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- grub_register_command ("write_dword", grub_cmd_write,
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- N_("ADDR VALUE [MASK]"),
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- N_("Write 32-bit VALUE to ADDR."));
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+ grub_register_command_lockdown ("write_dword", grub_cmd_write,
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+ N_("ADDR VALUE [MASK]"),
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+ N_("Write 32-bit VALUE to ADDR."));
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}
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GRUB_MOD_FINI(memrw)
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diff --git a/grub-core/kern/efi/sb.c b/grub-core/kern/efi/sb.c
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index ce3b7f6..5d7210a 100644
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--- a/grub-core/kern/efi/sb.c
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+++ b/grub-core/kern/efi/sb.c
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@@ -30,9 +30,6 @@
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static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
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-/* List of modules which cannot be loaded if UEFI secure boot mode is enabled. */
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-static const char * const disabled_mods[] = {"iorw", "memrw", NULL};
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-
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/*
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* Determine whether we're in secure boot mode.
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*
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@@ -121,53 +118,15 @@ shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
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void **context __attribute__ ((unused)),
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enum grub_verify_flags *flags)
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{
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- const char *b, *e;
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- int i;
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-
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*flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
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switch (type & GRUB_FILE_TYPE_MASK)
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{
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- case GRUB_FILE_TYPE_GRUB_MODULE:
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- /* Establish GRUB module name. */
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- b = grub_strrchr (io->name, '/');
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- e = grub_strrchr (io->name, '.');
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-
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- b = b ? (b + 1) : io->name;
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- e = e ? e : io->name + grub_strlen (io->name);
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- e = (e > b) ? e : io->name + grub_strlen (io->name);
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-
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- for (i = 0; disabled_mods[i]; i++)
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- if (!grub_strncmp (b, disabled_mods[i], grub_strlen (b) - grub_strlen (e)))
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- {
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- grub_error (GRUB_ERR_ACCESS_DENIED,
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- N_("module cannot be loaded in UEFI secure boot mode: %s"),
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- io->name);
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- return GRUB_ERR_ACCESS_DENIED;
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- }
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-
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- /* Fall through. */
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-
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- case GRUB_FILE_TYPE_ACPI_TABLE:
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- case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
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- *flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
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-
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- return GRUB_ERR_NONE;
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-
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case GRUB_FILE_TYPE_LINUX_KERNEL:
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case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
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case GRUB_FILE_TYPE_BSD_KERNEL:
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case GRUB_FILE_TYPE_XNU_KERNEL:
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case GRUB_FILE_TYPE_PLAN9_KERNEL:
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- for (i = 0; disabled_mods[i]; i++)
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- if (grub_dl_get (disabled_mods[i]))
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- {
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- grub_error (GRUB_ERR_ACCESS_DENIED,
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- N_("cannot boot due to dangerous module in memory: %s"),
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- disabled_mods[i]);
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- return GRUB_ERR_ACCESS_DENIED;
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- }
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-
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*flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
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/* Fall through. */
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--
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2.14.2
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