The maximum number of configurations and interfaces are fixed but there is
no out-of-bound checking to prevent a malicious USB device to report large
values for these and cause accesses outside the arrays' memory.
Fixes: CVE-2020-25647
Reported-by: Joseph Tartaro <joseph.tartaro@ioactive.com>
Reported-by: Ilja Van Sprundel <ivansprundel@ioactive.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
When a module is attempted to be removed its reference counter is always
decremented. This means that repeated rmmod invocations will cause the
module to be unloaded even if another module depends on it.
This may lead to a use-after-free scenario allowing an attacker to execute
arbitrary code and by-pass the UEFI Secure Boot protection.
While being there, add the extern keyword to some function declarations in
that header file.
Fixes: CVE-2020-25632
Reported-by: Chris Coulson <chris.coulson@canonical.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The shim_lock verifier validates the XNU kernels but no its extensions
and packages. Prevent these to be loaded when the GRUB is locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The gdbstub* commands allow to start and control a GDB stub running on
local host that can be used to connect from a remote debugger. Restrict
this functionality when the GRUB is locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The command can be used to get/set ATA disk parameters. Some of these can
be dangerous since change the disk behavior. Restrict it when locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This command can set PCI devices register values, which makes it dangerous
in a locked down configuration. Restrict it so can't be used on this setup.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
There are some more commands that should be restricted when the GRUB is
locked down. Following is the list of commands and reasons to restrict:
* fakebios: creates BIOS-like structures for backward compatibility with
existing OSes. This should not be allowed when locked down.
* loadbios: reads a BIOS dump from storage and loads it. This action
should not be allowed when locked down.
* devicetree: loads a Device Tree blob and passes it to the OS. It replaces
any Device Tree provided by the firmware. This also should
not be allowed when locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The cutmem and badram commands can be used to remove EFI memory regions
and potentially disable the UEFI Secure Boot. Prevent the commands to be
registered if the GRUB is locked down.
Fixes: CVE-2020-27779
Reported-by: Teddy Reed <teddy.reed@gmail.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The command is not allowed when lockdown is enforced. Otherwise an
attacker can instruct the GRUB to load an SSDT table to overwrite
the kernel lockdown configuration and later load and execute
unsigned code.
Fixes: CVE-2020-14372
Reported-by: Máté Kukri <km@mkukri.xyz>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
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>
If the UEFI Secure Boot is enabled then the GRUB must be locked down
to prevent executing code that can potentially be used to subvert its
verification mechanisms.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
It may be useful for scripts to determine whether the GRUB is locked
down or not. Add the lockdown variable which is set to "y" when the GRUB
is locked down.
Suggested-by: Dimitri John Ledkov <xnox@ubuntu.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
When the GRUB starts on a secure boot platform, some commands can be
used to subvert the protections provided by the verification mechanism and
could lead to booting untrusted system.
To prevent that situation, allow GRUB to be locked down. That way the code
may check if GRUB has been locked down and further restrict the commands
that are registered or what subset of their functionality could be used.
The lockdown support adds the following components:
* The grub_lockdown() function which can be used to lockdown GRUB if,
e.g., UEFI Secure Boot is enabled.
* The grub_is_lockdown() function which can be used to check if the GRUB
was locked down.
* A verifier that flags OS kernels, the GRUB modules, Device Trees and ACPI
tables as GRUB_VERIFY_FLAGS_DEFER_AUTH to defer verification to other
verifiers. These files are only successfully verified if another registered
verifier returns success. Otherwise, the whole verification process fails.
For example, PE/COFF binaries verification can be done by the shim_lock
verifier which validates the signatures using the shim_lock protocol.
However, the verification is not deferred directly to the shim_lock verifier.
The shim_lock verifier is hooked into the verification process instead.
* A set of grub_{command,extcmd}_lockdown functions that can be used by
code registering command handlers, to only register unsafe commands if
the GRUB has not been locked down.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The shim_lock module registers a verifier to call shim's verify, but the
handler is registered even when the shim_lock protocol was not installed.
This doesn't cause a NULL pointer dereference in shim_lock_write() because
the shim_lock_init() function just returns GRUB_ERR_NONE if sl isn't set.
But in that case there's no point to even register the shim_lock verifier
since won't do anything. Additionally, it is only useful when Secure Boot
is enabled.
Finally, don't assume that the shim_lock protocol will always be present
when the shim_lock_write() function is called, and check for it on every
call to this function.
Reported-by: Michael Chang <mchang@suse.com>
Reported-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
When building with --target=arm-linux-gnu --with-platform=coreboot
a linking error occurs caused by multiple definitions of the
ps2_state variable.
Mark them as static since they aren't used outside their compilation unit.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This header uses types defined in <grub/types.h> but does not include it,
which leads to compile errors like the following:
In file included from ../include/grub/cpu/linux.h:19,
from kern/efi/sb.c:21:
../include/grub/i386/linux.h:80:3: error: unknown type name ‘grub_uint64_t’
80 | grub_uint64_t addr;
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Nothing defined in the header file is used in the assembly code but it
may lead to build errors if some headers are included through this and
contains definitions that are not recognized by the assembler, e.g.:
../include/grub/types.h: Assembler messages:
../include/grub/types.h:76: Error: no such instruction: `typedef signed char grub_int8_t'
../include/grub/types.h:77: Error: no such instruction: `typedef short grub_int16_t'
../include/grub/types.h:78: Error: no such instruction: `typedef int grub_int32_t'
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This header uses types defined in <grub/types.h> but does not include it,
which leads to compile errors like the following:
../include/grub/cpu/linux.h:27:3: error: unknown type name ‘grub_uint32_t’
27 | grub_uint32_t code0; /* Executable code */
| ^~~~~~~~~~~~~
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The header uses the EXPORT_FUNC() macro defined in <grub/types.h> but
doesn't include it, which leads to the following compile error on arm:
../include/grub/cpu/system.h:12:13: error: ‘EXPORT_FUNC’ declared as function returning a function
12 | extern void EXPORT_FUNC(grub_arm_disable_caches_mmu) (void);
| ^~~~~~~~~~~
../include/grub/cpu/system.h:12:1: warning: parameter names (without types) in function declaration
12 | extern void EXPORT_FUNC(grub_arm_disable_caches_mmu) (void);
| ^~~~~~
make[3]: *** [Makefile:36581: kern/efi/kernel_exec-sb.o] Error 1
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Commit 781b3e5efc (tftp: Do not use priority queue) caused a regression
when fetching files over TFTP whose size is bigger than 65535 * block size.
grub> linux /images/pxeboot/vmlinuz
grub> echo $?
0
grub> initrd /images/pxeboot/initrd.img
error: timeout reading '/images/pxeboot/initrd.img'.
grub> echo $?
28
It is caused by the block number counter being a 16-bit field, which leads
to a maximum file size of ((1 << 16) - 1) * block size. Because GRUB sets
the block size to 1024 octets (by using the TFTP Blocksize Option from RFC
2348 [0]), the maximum file size that can be transferred is 67107840 bytes.
The TFTP PROTOCOL (REVISION 2) RFC 1350 [1] does not mention what a client
should do when a file size is bigger than the maximum, but most TFTP hosts
support the block number counter to be rolled over. That is, acking a data
packet with a block number of 0 is taken as if the 65356th block was acked.
It was working before because the block counter roll-over was happening due
an overflow. But that got fixed by the mentioned commit, which led to the
regression when attempting to fetch files larger than the maximum size.
To allow TFTP file transfers of unlimited size again, re-introduce a block
counter roll-over so the data packets are acked preventing the timeouts.
[0]: https://tools.ietf.org/html/rfc2348
[1]: https://tools.ietf.org/html/rfc1350
Fixes: 781b3e5efc (tftp: Do not use priority queue)
Suggested-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
Nested functions are not supported in C, but are permitted as an extension
in the GNU C dialect. Commit cb2f15c544 ("normal/main: Search for specific
config files for netboot") added a nested function which caused the build
to break when compiling with clang.
Break that out into a static helper function to make the code portable again.
Reported-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Daniel Axtens <dja@axtens.net>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The module is only enabled for x86_64, but there's nothing specific to
x86_64 in the implementation and can be enabled for all EFI platforms.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
If an existing variable is set with a value whose length is smaller than
the current value, a memory corruption can happen due copying padding '#'
characters outside of the environment block buffer.
This is caused by a wrong calculation of the previous free space position
after moving backward the characters that followed the old variable value.
That position is calculated to fill the remaining of the buffer with the
padding '#' characters. But since isn't calculated correctly, it can lead
to copies outside of the buffer.
The issue can be reproduced by creating a variable with a large value and
then try to set a new value that is much smaller:
$ grub2-editenv --version
grub2-editenv (GRUB) 2.04
$ grub2-editenv env create
$ grub2-editenv env set a="$(for i in {1..500}; do var="b$var"; done; echo $var)"
$ wc -c env
1024 grubenv
$ grub2-editenv env set a="$(for i in {1..50}; do var="b$var"; done; echo $var)"
malloc(): corrupted top size
Aborted (core dumped)
$ wc -c env
0 grubenv
Reported-by: Renaud Métrich <rmetrich@redhat.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is just a preparatory patch to move the functions higher in the file,
since these will be called by the grub_prepare_for_text_output() function
that will be introduced in a later patch.
The logic is unchanged by this patch. Functions definitions are just moved
to avoid a forward declaration in a later patch, keeping the code clean.
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The DHCP Options and BOOTP Vendor Extensions enum values are a mixture of
decimal and hexadecimal numbers. Change this to consistently use decimal
numbers for all since that is how these values are defined by RFC 2132.
Suggested-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
The common datetime helper functions are currently included in the normal
module, but this makes any other module that calls these functions to have
a dependency with the normal module only for this reason.
Since the normal module does a lot of stuff, it calls functions from other
modules. But since other modules may depend on it for calling the datetime
helpers, this could lead to circular dependencies between modules.
As an example, when platform == xen the grub_get_datetime() function from
the datetime module calls to the grub_unixtime2datetime() helper function
from the normal module. Which leads to the following module dependency:
datetime -> normal
and send_dhcp_packet() from the net module calls the grub_get_datetime()
function, which leads to the following module dependency:
net -> datetime -> normal
but that means that the normal module is not allowed to depend on net or
any other module that depends on it due the transitive dependency caused
by datetime. A recent patch attempted to add support to fetch the config
file over the network, which leads to the following circular dependency:
normal -> net -> datetime -> normal
So having the datetime helpers in the normal module makes it quite fragile
and easy to add circular dependencies like these, that break the build due
the genmoddep.awk script catching the issues.
Fix this by taking the datetime helper functions out of the normal module
and instead add them to the datetime module itself. Besides fixing these
issues, it makes more sense to have these helper functions there anyways.
Reported-by: Daniel Kiper <daniel.kiper@oracle.com>
Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
