u-boot.git/lib/efi_loader/efi_runtime.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: 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: avoid duplicate weak invalidate_icache_all()

2024-06-19T19:10:23+00:00

If multiple weak implementations of a weak function exist, it is unclear
which one the linker should chose. cmd/cache.c already defines a weak
invalidate_icache_all().

We don't need a call to invalidate_icache_all() on x86.
ARM, RISC-V, and Sandbox provide an implementation.

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

efi_loader: enable QueryVariableInfo at runtime for file backed variables

2024-05-01T05:40:05+00:00

Since commit c28d32f946f0 ("efi_loader: conditionally enable SetvariableRT")
we are enabling the last bits of missing runtime services.
Add support for QueryVariableInfo which we already support at boottime
and we just need to mark some fucntions available at runtime and move
some checks around.

It's worth noting that pointer checks for maxmimum and remaining
variable storage aren't when we store variables on the RPMB, since the
Secure World backend is already performing them.

Signed-off-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: Add OS notifications for SetVariable at runtime

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

Previous patches enable SetVariable at runtime using a volatile storage
backend using EFI_RUNTIME_SERVICES_DATA allocared memory. Since there's
no recommendation from the spec on how to notify the OS, add a volatile
EFI variable that contains the filename relative to the ESP. OS'es
can use that file and update it at runtime

$~ efivar -p -n b2ac5fc9-92b7-4acd-aeac-11e818c3130c-RTStorageVolatile
GUID: b2ac5fc9-92b7-4acd-aeac-11e818c3130c
Name: "RTStorageVolatile"
Attributes:
	Boot Service Access
	Runtime Service Access
Value:
00000000  75 62 6f 6f 74 65 66 69  2e 76 61 72 00           |ubootefi.var.   |

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

efi_loader: conditionally enable SetvariableRT

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

When we store EFI variables on file we don't allow SetVariable at runtime,
since the OS doesn't know how to access or write that file. At the same
time keeping the U-Boot drivers alive in runtime sections and performing
writes from the firmware is dangerous -- if at all possible.

For GetVariable at runtime we copy runtime variables in RAM and expose them
to the OS. Add a Kconfig option and provide SetVariable at runtime using
the same memory backend. The OS will be responsible for syncing the RAM
contents to the file, otherwise any changes made during runtime won't
persist reboots.

It's worth noting that the variable store format is defined in EBBR [0]
and authenticated variables are explicitly prohibited, since they have
to be stored on a medium that's tamper and rollback protected.

- pre-patch
$~ mount | grep efiva
efivarfs on /sys/firmware/efi/efivars type efivarfs (ro,nosuid,nodev,noexec,relatime)

$~ efibootmgr -n 0001
Could not set BootNext: Read-only file system

- post-patch
$~ mount | grep efiva
efivarfs on /sys/firmware/efi/efivars type efivarfs (rw,nosuid,nodev,noexec,relatime)

$~ efibootmgr -n 0001
BootNext: 0001
BootCurrent: 0000
BootOrder: 0000,0001
Boot0000* debian HD(1,GPT,bdae5610-3331-4e4d-9466-acb5caf0b4a6,0x800,0x100000)/File(EFI\debian\grubaa64.efi)
Boot0001* virtio 0 VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,0000000000000000)/VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,850000001f000000)/VenHw(e61d73b9-a384-4acc-aeab-82e828f3628b,1600850000000000){auto_created_boot_option}

$~ efivar -p -n 8be4df61-93ca-11d2-aa0d-00e098032b8c-BootNext
GUID: 8be4df61-93ca-11d2-aa0d-00e098032b8c
Name: "BootNext"
Attributes:
Non-Volatile
Boot Service Access
Runtime Service Access
Value:
00000000 01 00

FWTS runtime results
Skipped tests are for SetVariable which is now supported
'Passed' test is for QueryVariableInfo which is not yet supported

Test: UEFI miscellaneous runtime service interface tests.
Test for UEFI miscellaneous runtime service interfaces 6 skipped
Stress test for UEFI miscellaneous runtime service i.. 1 skipped
Test GetNextHighMonotonicCount with invalid NULL par.. 1 skipped
Test UEFI miscellaneous runtime services unsupported.. 1 passed
Test: UEFI Runtime service variable interface tests.
Test UEFI RT service get variable interface. 1 passed
Test UEFI RT service get next variable name interface. 4 passed
Test UEFI RT service set variable interface. 8 passed
Test UEFI RT service query variable info interface. 1 skipped
Test UEFI RT service variable interface stress test. 2 passed
Test UEFI RT service set variable interface stress t.. 4 passed
Test UEFI RT service query variable info interface s.. 1 skipped
Test UEFI RT service get variable interface, invalid.. 5 passed
Test UEFI RT variable services unsupported status. 1 passed, 3 skipped

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

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

efi_loader: access __efi_runtime_rel_start/stop without &

2024-04-08T11:05:50+00:00

A symbol defined in a linker script (e.g. __efi_runtime_rel_start = .;)
is only a symbol, not a variable and should not be dereferenced.
The common practice is either define it as
extern uint32_t __efi_runtime_rel_start or
extern char __efi_runtime_rel_start[] and access it as
&__efi_runtime_rel_start or __efi_runtime_rel_start respectively.

So let's access it properly since we define it as an array

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

arm: fix __efi_runtime_rel_start/end definitions

2024-03-29T14:39:25+00:00

__efi_runtime_rel_start/end are defined as c variables for arm7 only in
order to force the compiler emit relative references. However, defining
those within a section definition will do the same thing since [0].
On top of that the v8 linker scripts define it as a symbol.

So let's remove the special sections from the linker scripts, the
variable definitions from sections.c and define them as a symbols within
the correct section.

[0] binutils commit 6b3b0ab89663 ("Make linker assigned symbol dynamic only for shared object")

Suggested-by: Sam Edwards 
Reviewed-by: Sam Edwards 
Tested-by: Sam Edwards  # Binary output identical
Reviewed-by: Richard Henderson 
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