u-boot.git/lib/efi_loader/efi_var_mem.c, 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_loader: remove comparisons to string literals from runtime

2025-02-20T08:22:53+00:00

For EFI runtime services, we manage to preserve string literals
by placing the .efi_runtime section just before .data and preserving
it when marking the runtime memory by marking surrounding boottime
code as runtime. This is ok for now but will break if we update any
linker scripts and decouple .text and .runtime sections.

So let's define the strings we used to compare in the appropriate
section for runtime services

Signed-off-by: Ilias Apalodimas 
Reviewed-by: Mark Kettenis

efi_loader: use LOGC_EFI consistently

2025-01-26T10:06:56+00:00

The log category should be LOGC_EFI all over the EFI sub-system.

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

efi_loader: address coverity report 492766 for dead code

2024-05-01T05:39:27+00:00

The check of the return code is already done a few lines above.
Although it doesn't cause any functional issues, remove the superfluous
checks

Addresses-Coverity-ID: 492766 Control flow issues  (DEADCODE)
Signed-off-by: Ilias Apalodimas 
Reviewed-by: Heinrich Schuchardt

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: Remove

2023-12-21T13:54:37+00:00

We largely do not need  in these files, so drop it. The only
exception here is that efi_freestanding.c needs  and had
been getting that via .

Reviewed-by: Simon Glass 
Signed-off-by: Tom Rini

efi_loader: Avoid underflow when calculating remaining var store size

2023-07-09T01:53:08+00:00

The efi_var_mem_free() function calculates the available size for a new
EFI variable by subtracting the occupied buffer size and the overhead
for a new variable from the maximum buffer size set in Kconfig. This
is then returned as QueryVariableInfo()'s RemainingVariableStorageSize
output.

This can underflow as the calculation is done in and processed as
unsigned integer types. Check for underflow before doing the subtraction
and return zero if there's no space.

Fixes: f1f990a8c958 ("efi_loader: memory buffer for variables")
Signed-off-by: Alper Nebi Yasak 
Reviewed-by: Heinrich Schuchardt

efi_loader: avoid buffer overrun in efi_var_mem_compare

2023-02-19T20:15:15+00:00

We should not scan beyond the end of string name.

Signed-off-by: Heinrich Schuchardt

efi_loader: use u16_strlen() in efi_var_mem_ins()

2022-12-29T11:52:39+00:00

Don't duplicate library functionality.

Signed-off-by: Heinrich Schuchardt

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