u-boot.git/include/efi_variable.h, branch master

efi_loader: avoid superfluous variable store writes on unchanged data

2026-03-14T07:14:20+00:00

Every SetVariable() call triggers efi_var_mem_ins() followed by
efi_var_to_storage(), even when the variable value is not actually
changing. This is unfriendly to flash-backed stores that suffer
wear from unnecessary erase/write cycles.

Add a change-detection path to efi_var_mem_ins(): when size2 == 0
(i.e. not an append) and the caller passes a non-NULL changep flag,
look up the existing variable and compare attributes, length, time
and data byte-by-byte. If everything matches, set *changep = false
and return EFI_SUCCESS without touching the variable buffer.

Both efi_set_variable_int() and efi_set_variable_runtime() now
check the flag and skip efi_var_mem_del() / efi_var_to_storage()
when nothing changed.

Introduce efi_memcmp_runtime() - a runtime-safe byte-by-byte memory
comparison helper, following the same pattern as the existing
efi_memcpy_runtime(). The standard memcmp() is not available after
ExitBootServices() and calling it from Linux will crash.

Tested-by: Heinrich Schuchardt 
Reviewed-by: Heinrich Schuchardt 
Signed-off-by: Michal Simek 
Reviewed-by: Ilias Apalodimas

efi_var: Unify read/write access helper function

2026-02-15T08:15:28+00:00

efi_var_to/from_file() suggest method where variables are placed. But there
is no reason for it and generic name can be used to wire also different
locations for variables.

Signed-off-by: Michal Simek 
Reviewed-by: Ilias Apalodimas 
Tested-by: Neil Armstrong  # on AML-S905D3-CC
Reviewed-by: Heinrich Schuchardt

efi_var_file: refactor to move buffer functions

2026-02-15T08:14:31+00:00

Currently efi_var_file.c has functions to store/read
EFI variables to/from memory buffer. These functions
can be used with other EFI variable stores so move
them out to efi_var_common.c

Signed-off-by: Shantur Rathore 
Signed-off-by: Michal Simek 
Tested-by: Neil Armstrong  # on AML-S905D3-CC
Reviewed-by: Ilias Apalodimas 
Reviewed-by: Heinrich Schuchardt

efi_loader: correct efi_set_variable_int() description

2024-09-21T08:59:06+00:00

The name used in the function description must match the function.

Signed-off-by: Heinrich Schuchardt 
Reviewed-by: Ilias Apalodimas

efi_loader: add an EFI variable with the file contents

2024-04-20T06:22:24+00:00

Previous patches enabled SetVariableRT using a RAM backend.
Although EBBR [0] defines a variable format we can teach userspace tools
and write the altered variables, it's better if we skip the ABI
requirements completely.

So let's add a new variable, in its own namespace called "VarToFile"
which contains a binary dump of the updated RT, BS and, NV variables
and will be updated when GetVariable is called.

Some adjustments are needed to do that.
Currently we discard BS-only variables in EBS(). We need to preserve
those on the RAM backend that exposes the variables. Since BS-only
variables can't appear at runtime we need to move the memory masking
checks from efi_var_collect() to efi_get_next_variable_name_mem()/
efi_get_variable_mem() and do the filtering at runtime.

We also need an efi_var_collect() variant available at runtime, in order
to construct the "VarToFile" buffer on the fly.

All users and applications (for linux) have to do when updating a variable
is dd that variable in the file described by "RTStorageVolatile".

Linux efivarfs uses a first 4 bytes of the output to represent attributes
in little-endian format. So, storing variables works like this:

$~ efibootmgr -n 0001
$~ dd if=/sys/firmware/efi/efivars/VarToFile-b2ac5fc9-92b7-4acd-aeac-11e818c3130c of=/boot/efi/ubootefi.var skip=4 bs=1

[0] https://arm-software.github.io/ebbr/index.html#document-chapter5-variable-storage

Suggested-by: Ard Biesheuvel  # dumping all variables to a variable
Co-developed-by: Heinrich Schuchardt  # contributed on efi_var_collect_mem()
Signed-off-by: Heinrich Schuchardt 
Signed-off-by: Ilias Apalodimas

efi_loader: EFI_VARIABLE_READ_ONLY should be 32bit

2024-04-08T11:03:31+00:00

GetVariable() and SetVariable() only accept a 32bit value for attributes.
It makes not sense to define EFI_VARIABLE_READ_ONLY as unsigned long.

Signed-off-by: Heinrich Schuchardt 
Reviewed-by: Ilias Apalodimas

efi_loader: fix efi_get_next_variable_name_mem()

2022-12-20T15:06:48+00:00

The VariableNameSize parameter is in bytes but u16_strnlen() counts u16.

Fix the parameter check for null termination.

Signed-off-by: Heinrich Schuchardt 
Reviewed-by: Ilias Apalodimas

efi_loader: function to get GUID for variable name

2021-10-25T19:13:06+00:00

In multiple places we need the default GUID matching a variable name.
The patch provides a library function. For secure boot related variables
like 'PK', 'KEK', 'db' a lookup table is used. For all other variable
names EFI_GLOBAL_VARIABLE is returned.

Signed-off-by: Heinrich Schuchardt 
Reviewed-by: Ilias Apalodimas

efi_loader: treat UEFI variable name as const

2021-10-25T19:13:06+00:00

UEFI variable names are typically constants and hence should be defined as
const. Unfortunately some of our API functions do not define the parameters
for UEFI variable names as const. This requires unnecessary conversions.

Adjust parameters of several internal functions to tre UEFI variable names
as const.

Signed-off-by: Heinrich Schuchardt 
Reviewed-by: Ilias Apalodimas

efi_loader: efi_auth_var_type for AuditMode, DeployedMode

2021-09-04T10:03:57+00:00

Writing variables AuditMode and DeployedMode serves to switch between
Secure Boot modes. Provide a separate value for these in efi_auth_var_type.

With this patch the variables will not be read from from file even if they
are marked as non-volatile by mistake.

Signed-off-by: Heinrich Schuchardt