linux-kernel - [PATCH v4 2/7] efi/runtime-wrappers: Keep track of the efi_runtime

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Message-ID: <20250924152651.3328941-11-ardb+git@google.com>
Date: Wed, 24 Sep 2025 17:26:54 +0200
From: Ard Biesheuvel <ardb+git@...gle.com>
To: linux-efi@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
	Ard Biesheuvel <ardb@...nel.org>, Will Deacon <will@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Peter Zijlstra <peterz@...radead.org>, 
	Catalin Marinas <catalin.marinas@....com>, Mark Brown <broonie@...nel.org>
Subject: [PATCH v4 2/7] efi/runtime-wrappers: Keep track of the
 efi_runtime_lock owner

From: Ard Biesheuvel <ardb@...nel.org>

The EFI runtime wrappers use a file local semaphore to serialize access
to the EFI runtime services. This means that any calls to the arch
wrappers around the runtime services will also be serialized, removing
the need for redundant locking.

For robustness, add a facility that allows those arch wrappers to assert
that the semaphore was taken by the current task.

Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 drivers/firmware/efi/runtime-wrappers.c | 17 ++++++++++++++++-
 include/linux/efi.h                     |  2 ++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 708b777857d3..da8d29621644 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -202,6 +202,8 @@ void efi_call_virt_check_flags(unsigned long flags, const void *caller)
  */
 static DEFINE_SEMAPHORE(efi_runtime_lock, 1);
 
+static struct task_struct *efi_runtime_lock_owner;
+
 /*
  * Expose the EFI runtime lock to the UV platform
  */
@@ -219,6 +221,8 @@ static void __nocfi efi_call_rts(struct work_struct *work)
 	efi_status_t status = EFI_NOT_FOUND;
 	unsigned long flags;
 
+	efi_runtime_lock_owner = current;
+
 	arch_efi_call_virt_setup();
 	flags = efi_call_virt_save_flags();
 
@@ -310,6 +314,7 @@ static void __nocfi efi_call_rts(struct work_struct *work)
 
 	efi_rts_work.status = status;
 	complete(&efi_rts_work.efi_rts_comp);
+	efi_runtime_lock_owner = NULL;
 }
 
 static efi_status_t __efi_queue_work(enum efi_rts_ids id,
@@ -444,8 +449,10 @@ virt_efi_set_variable_nb(efi_char16_t *name, efi_guid_t *vendor, u32 attr,
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
+	efi_runtime_lock_owner = current;
 	status = efi_call_virt_pointer(efi.runtime, set_variable, name, vendor,
 				       attr, data_size, data);
+	efi_runtime_lock_owner = NULL;
 	up(&efi_runtime_lock);
 	return status;
 }
@@ -481,9 +488,11 @@ virt_efi_query_variable_info_nb(u32 attr, u64 *storage_space,
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
+	efi_runtime_lock_owner = current;
 	status = efi_call_virt_pointer(efi.runtime, query_variable_info, attr,
 				       storage_space, remaining_space,
 				       max_variable_size);
+	efi_runtime_lock_owner = NULL;
 	up(&efi_runtime_lock);
 	return status;
 }
@@ -509,12 +518,13 @@ virt_efi_reset_system(int reset_type, efi_status_t status,
 		return;
 	}
 
+	efi_runtime_lock_owner = current;
 	arch_efi_call_virt_setup();
 	efi_rts_work.efi_rts_id = EFI_RESET_SYSTEM;
 	arch_efi_call_virt(efi.runtime, reset_system, reset_type, status,
 			   data_size, data);
 	arch_efi_call_virt_teardown();
-
+	efi_runtime_lock_owner = NULL;
 	up(&efi_runtime_lock);
 }
 
@@ -587,3 +597,8 @@ efi_call_acpi_prm_handler(efi_status_t (__efiapi *handler_addr)(u64, void *),
 }
 
 #endif
+
+void efi_runtime_assert_lock_held(void)
+{
+	WARN_ON(efi_runtime_lock_owner != current);
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a98cc39e7aaa..b23ff8b83219 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1126,6 +1126,8 @@ static inline bool efi_runtime_disabled(void) { return true; }
 extern void efi_call_virt_check_flags(unsigned long flags, const void *caller);
 extern unsigned long efi_call_virt_save_flags(void);
 
+void efi_runtime_assert_lock_held(void);
+
 enum efi_secureboot_mode {
 	efi_secureboot_mode_unset,
 	efi_secureboot_mode_unknown,
-- 
2.51.0.534.gc79095c0ca-goog