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efi: Use grub_is_lockdown() instead of hardcoding a disabled modules list

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Now the GRUB can check if it has been locked down and this can be used to
prevent executing commands that can be utilized to circumvent the UEFI
Secure Boot mechanisms. So, instead of hardcoding a list of modules that
have to be disabled, prevent the usage of commands that can be dangerous.

This not only allows the commands to be disabled on other platforms, but
also properly separate the concerns. Since the shim_lock verifier logic
should be only about preventing to run untrusted binaries and not about
defining these kind of policies.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This commit is contained in:
Javier Martinez Canillas authored and Daniel Kiper committed 2021-03-02 15:54:15 +01:00
1 parent 98b00a403c
commit 8f73052885
5 files changed
+32 -67
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grub-core/commands/i386/wrmsr.c
+3 -2
View File
@@ -24,6 +24,7 @@
#include <grub/env.h>
#include <grub/command.h>
#include <grub/extcmd.h>
#include <grub/lockdown.h>
#include <grub/i18n.h>
#include <grub/i386/cpuid.h>
#include <grub/i386/wrmsr.h>
@@ -83,8 +84,8 @@ grub_cmd_msr_write (grub_command_t cmd __attribute__ ((unused)), int argc, char
GRUB_MOD_INIT(wrmsr)
{
cmd_write = grub_register_command ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
N_("Write a value to a CPU model specific register."));
cmd_write = grub_register_command_lockdown ("wrmsr", grub_cmd_msr_write, N_("ADDR VALUE"),
N_("Write a value to a CPU model specific register."));
}
GRUB_MOD_FINI(wrmsr)
grub-core/commands/iorw.c
+10 -9
View File
@@ -23,6 +23,7 @@
#include <grub/env.h>
#include <grub/cpu/io.h>
#include <grub/i18n.h>
#include <grub/lockdown.h>
GRUB_MOD_LICENSE ("GPLv3+");
@@ -131,17 +132,17 @@ GRUB_MOD_INIT(memrw)
N_("PORT"), N_("Read 32-bit value from PORT."),
options);
cmd_write_byte =
grub_register_command ("outb", grub_cmd_write,
N_("PORT VALUE [MASK]"),
N_("Write 8-bit VALUE to PORT."));
grub_register_command_lockdown ("outb", grub_cmd_write,
N_("PORT VALUE [MASK]"),
N_("Write 8-bit VALUE to PORT."));
cmd_write_word =
grub_register_command ("outw", grub_cmd_write,
N_("PORT VALUE [MASK]"),
N_("Write 16-bit VALUE to PORT."));
grub_register_command_lockdown ("outw", grub_cmd_write,
N_("PORT VALUE [MASK]"),
N_("Write 16-bit VALUE to PORT."));
cmd_write_dword =
grub_register_command ("outl", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 32-bit VALUE to PORT."));
grub_register_command_lockdown ("outl", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 32-bit VALUE to PORT."));
}
GRUB_MOD_FINI(memrw)
grub-core/commands/memrw.c
+10 -9
View File
@@ -22,6 +22,7 @@
#include <grub/extcmd.h>
#include <grub/env.h>
#include <grub/i18n.h>
#include <grub/lockdown.h>
GRUB_MOD_LICENSE ("GPLv3+");
@@ -133,17 +134,17 @@ GRUB_MOD_INIT(memrw)
N_("ADDR"), N_("Read 32-bit value from ADDR."),
options);
cmd_write_byte =
grub_register_command ("write_byte", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 8-bit VALUE to ADDR."));
grub_register_command_lockdown ("write_byte", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 8-bit VALUE to ADDR."));
cmd_write_word =
grub_register_command ("write_word", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 16-bit VALUE to ADDR."));
grub_register_command_lockdown ("write_word", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 16-bit VALUE to ADDR."));
cmd_write_dword =
grub_register_command ("write_dword", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 32-bit VALUE to ADDR."));
grub_register_command_lockdown ("write_dword", grub_cmd_write,
N_("ADDR VALUE [MASK]"),
N_("Write 32-bit VALUE to ADDR."));
}
GRUB_MOD_FINI(memrw)
grub-core/kern/efi/sb.c
-41
View File
@@ -30,9 +30,6 @@
static grub_efi_guid_t shim_lock_guid = GRUB_EFI_SHIM_LOCK_GUID;
/* List of modules which cannot be loaded if UEFI secure boot mode is enabled. */
static const char * const disabled_mods[] = {"iorw", "memrw", "wrmsr", NULL};
/*
* Determine whether we're in secure boot mode.
*
@@ -121,53 +118,15 @@ shim_lock_verifier_init (grub_file_t io __attribute__ ((unused)),
void **context __attribute__ ((unused)),
enum grub_verify_flags *flags)
{
const char *b, *e;
int i;
*flags = GRUB_VERIFY_FLAGS_SKIP_VERIFICATION;
switch (type & GRUB_FILE_TYPE_MASK)
{
case GRUB_FILE_TYPE_GRUB_MODULE:
/* Establish GRUB module name. */
b = grub_strrchr (io->name, '/');
e = grub_strrchr (io->name, '.');
b = b ? (b + 1) : io->name;
e = e ? e : io->name + grub_strlen (io->name);
e = (e > b) ? e : io->name + grub_strlen (io->name);
for (i = 0; disabled_mods[i]; i++)
if (!grub_strncmp (b, disabled_mods[i], grub_strlen (b) - grub_strlen (e)))
{
grub_error (GRUB_ERR_ACCESS_DENIED,
N_("module cannot be loaded in UEFI secure boot mode: %s"),
io->name);
return GRUB_ERR_ACCESS_DENIED;
}
/* Fall through. */
case GRUB_FILE_TYPE_ACPI_TABLE:
case GRUB_FILE_TYPE_DEVICE_TREE_IMAGE:
*flags = GRUB_VERIFY_FLAGS_DEFER_AUTH;
return GRUB_ERR_NONE;
case GRUB_FILE_TYPE_LINUX_KERNEL:
case GRUB_FILE_TYPE_MULTIBOOT_KERNEL:
case GRUB_FILE_TYPE_BSD_KERNEL:
case GRUB_FILE_TYPE_XNU_KERNEL:
case GRUB_FILE_TYPE_PLAN9_KERNEL:
for (i = 0; disabled_mods[i]; i++)
if (grub_dl_get (disabled_mods[i]))
{
grub_error (GRUB_ERR_ACCESS_DENIED,
N_("cannot boot due to dangerous module in memory: %s"),
disabled_mods[i]);
return GRUB_ERR_ACCESS_DENIED;
}
*flags = GRUB_VERIFY_FLAGS_SINGLE_CHUNK;
/* Fall through. */