The GRUB may use TPM to verify the integrity of boot components and the
result can determine whether a previously sealed key can be released. If
everything checks out, showing nothing has been tampered with, the key
is released and GRUB unlocks the encrypted root partition for the next
stage of booting.
However, the liberal Command Line Interface (CLI) can be misused by
anyone in this case to access files in the encrypted partition one way
or another. Despite efforts to keep the CLI secure by preventing utility
command output from leaking file content, many techniques in the wild
could still be used to exploit the CLI, enabling attacks or learning
methods to attack. It's nearly impossible to account for all scenarios
where a hack could be applied.
Therefore, to mitigate potential misuse of the CLI after the root device
has been successfully unlocked via TPM, the user should be required to
authenticate using the LUKS password. This added layer of security
ensures that only authorized users can access the CLI reducing the risk
of exploitation or unauthorized access to the encrypted partition.
Fixes: CVE-2024-49504
Signed-off-by: Michael Chang <mchang@suse.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Add functionality to disable command line interface access and editing of GRUB
menu entries if GRUB image is built with --disable-cli.
Signed-off-by: Alec Brown <alec.r.brown@oracle.com>
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The "ground truth" stack protector cookie value is kept in a global
variable, and loaded in every function prologue and epilogue to store
it into resp. compare it with the stack slot holding the cookie.
If the comparison fails, the program aborts, and this might occur
spuriously when the global variable changes values between the entry and
exit of a function. This implies that assigning the global variable at
boot should not involve any instrumented function calls, unless special
care is taken to ensure that the live call stack is synchronized, which
is non-trivial.
So avoid any function calls, including grub_memcpy(), which is
unnecessary given that the stack cookie is always a suitably aligned
variable of the native word size.
While at it, leave the last byte 0x0 to avoid inadvertent unbounded
strings on the stack.
Note that the use of __attribute__((optimize)) is described as
unsuitable for production use in the GCC documentation, so let's drop
this as well now that it is no longer needed.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
GRUB EFI builds are now often used in combination with flicker-free
boot, but this breaks with upstream GRUB because the "Welcome to GRUB!"
message will kick the EFI fb into text mode and show the msg, breaking
the flicker-free experience.
EFI systems are so fast, that when the menu or the countdown are
enabled the message will be immediately overwritten, so in these cases
not printing the message does not matter.
And in case when the timeout_style is set to TIMEOUT_STYLE_HIDDEN,
the user has asked GRUB to be quiet (for example to allow flickfree
boot) and thus the message should not be printed.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Robbie Harwood <rharwood@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Move verifiers API from a module to the kernel image, so it can be
used there as well. There are no functional changes in this patch.
Signed-off-by: Marco A Benatto <mbenatto@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
