[PATCH v4] efi: implement mandatory locking for UEFI Runtime Services

[Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>]

According to section 7.1 of the UEFI spec, Runtime Services are not fully
reentrant, and there are particular combinations of calls that need to be
serialized. Use a spinlock to serialize all Runtime Services with respect
to all others, even if this is more than strictly needed.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
---
 arch/x86/include/asm/efi.h              |   2 +
 drivers/firmware/efi/runtime-wrappers.c | 154 +++++++++++++++++++++++++++++---
 2 files changed, 146 insertions(+), 10 deletions(-)

diff --git a/arch/x86/include/asm/efi.h b/arch/x86/include/asm/efi.h
index 044a2fd3c5fe..b39ee5f2c02d 100644
--- a/arch/x86/include/asm/efi.h
+++ b/arch/x86/include/asm/efi.h
@@ -86,6 +86,8 @@ extern void __iomem *efi_ioremap(unsigned long addr, unsigned long size,
 
 #endif /* CONFIG_X86_32 */
 
+#define efi_in_nmi()	in_nmi()
+
 extern int add_efi_memmap;
 extern struct efi_scratch efi_scratch;
 extern void efi_set_executable(efi_memory_desc_t *md, bool executable);
diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 10daa4bbb258..9694cba665c4 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -14,11 +14,83 @@
  * This file is released under the GPLv2.
  */
 
+#include <linux/bug.h>
 #include <linux/efi.h>
-#include <linux/spinlock.h>             /* spinlock_t */
+#include <linux/mutex.h>
+#include <linux/spinlock.h>
 #include <asm/efi.h>
 
 /*
+ * According to section 7.1 of the UEFI spec, Runtime Services are not fully
+ * reentrant, and there are particular combinations of calls that need to be
+ * serialized. (source: UEFI Specification v2.4A)
+ *
+ * Table 31. Rules for Reentry Into Runtime Services
+ * +------------------------------------+-------------------------------+
+ * | If previous call is busy in	| Forbidden to call		|
+ * +------------------------------------+-------------------------------+
+ * | Any				| SetVirtualAddressMap()	|
+ * +------------------------------------+-------------------------------+
+ * | ConvertPointer()			| ConvertPointer()		|
+ * +------------------------------------+-------------------------------+
+ * | SetVariable()			| ResetSystem()			|
+ * | UpdateCapsule()			|				|
+ * | SetTime()				|				|
+ * | SetWakeupTime()			|				|
+ * | GetNextHighMonotonicCount()	|				|
+ * +------------------------------------+-------------------------------+
+ * | GetVariable()			| GetVariable()			|
+ * | GetNextVariableName()		| GetNextVariableName()		|
+ * | SetVariable()			| SetVariable()			|
+ * | QueryVariableInfo()		| QueryVariableInfo()		|
+ * | UpdateCapsule()			| UpdateCapsule()		|
+ * | QueryCapsuleCapabilities()		| QueryCapsuleCapabilities()	|
+ * | GetNextHighMonotonicCount()	| GetNextHighMonotonicCount()	|
+ * +------------------------------------+-------------------------------+
+ * | GetTime()				| GetTime()			|
+ * | SetTime()				| SetTime()			|
+ * | GetWakeupTime()			| GetWakeupTime()		|
+ * | SetWakeupTime()			| SetWakeupTime()		|
+ * +------------------------------------+-------------------------------+
+ *
+ * Due to the fact that the EFI pstore may write to the variable store in
+ * interrupt context, we need to use a spinlock for at least the groups that
+ * contain SetVariable() and QueryVariableInfo(). That leaves little else, as
+ * none of the remaining functions are actually ever called at runtime.
+ * So let's just use a single spinlock to serialize all Runtime Services calls.
+ */
+static DEFINE_SPINLOCK(efi_runtime_lock);
+
+/*
+ * Some runtime services calls can be reentrant under NMI, even if the table
+ * above says they are not. (source: UEFI Specification v2.4A)
+ *
+ * Table 32. Functions that may be called after Machine Check, INIT and NMI
+ * +----------------------------+------------------------------------------+
+ * | Function			| Called after Machine Check, INIT and NMI |
+ * +----------------------------+------------------------------------------+
+ * | GetTime()			| Yes, even if previously busy.		   |
+ * | GetVariable()		| Yes, even if previously busy		   |
+ * | GetNextVariableName()	| Yes, even if previously busy		   |
+ * | QueryVariableInfo()	| Yes, even if previously busy		   |
+ * | SetVariable()		| Yes, even if previously busy		   |
+ * | UpdateCapsule()		| Yes, even if previously busy		   |
+ * | QueryCapsuleCapabilities()	| Yes, even if previously busy		   |
+ * | ResetSystem()		| Yes, even if previously busy		   |
+ * +----------------------------+------------------------------------------+
+ *
+ * In order to prevent deadlocks under NMI, the wrappers for these functions
+ * may only grab the efi_runtime_lock or rtc_lock spinlocks if !efi_in_nmi().
+ * However, not all of the services listed are reachable through NMI code paths,
+ * so the the special handling as suggested by the UEFI spec is only implemented
+ * for QueryVariableInfo() and SetVariable(), as these can be reached in NMI
+ * context through efi_pstore_write().
+ */
+#ifndef efi_in_nmi
+#define efi_in_nmi()	(0)
+#endif
+
+/*
  * As per commit ef68c8f87ed1 ("x86: Serialize EFI time accesses on rtc_lock"),
  * the EFI specification requires that callers of the time related runtime
  * functions serialize with other CMOS accesses in the kernel, as the EFI time
@@ -32,7 +104,9 @@ static efi_status_t virt_efi_get_time(efi_time_t *tm, efi_time_cap_t *tc)
 	efi_status_t status;
 
 	spin_lock_irqsave(&rtc_lock, flags);
+	spin_lock(&efi_runtime_lock);
 	status = efi_call_virt(get_time, tm, tc);
+	spin_unlock(&efi_runtime_lock);
 	spin_unlock_irqrestore(&rtc_lock, flags);
 	return status;
 }
@@ -43,7 +117,9 @@ static efi_status_t virt_efi_set_time(efi_time_t *tm)
 	efi_status_t status;
 
 	spin_lock_irqsave(&rtc_lock, flags);
+	spin_lock(&efi_runtime_lock);
 	status = efi_call_virt(set_time, tm);
+	spin_unlock(&efi_runtime_lock);
 	spin_unlock_irqrestore(&rtc_lock, flags);
 	return status;
 }
@@ -56,7 +132,9 @@ static efi_status_t virt_efi_get_wakeup_time(efi_bool_t *enabled,
 	efi_status_t status;
 
 	spin_lock_irqsave(&rtc_lock, flags);
+	spin_lock(&efi_runtime_lock);
 	status = efi_call_virt(get_wakeup_time, enabled, pending, tm);
+	spin_unlock(&efi_runtime_lock);
 	spin_unlock_irqrestore(&rtc_lock, flags);
 	return status;
 }
@@ -67,7 +145,9 @@ static efi_status_t virt_efi_set_wakeup_time(efi_bool_t enabled, efi_time_t *tm)
 	efi_status_t status;
 
 	spin_lock_irqsave(&rtc_lock, flags);
+	spin_lock(&efi_runtime_lock);
 	status = efi_call_virt(set_wakeup_time, enabled, tm);
+	spin_unlock(&efi_runtime_lock);
 	spin_unlock_irqrestore(&rtc_lock, flags);
 	return status;
 }
@@ -78,14 +158,27 @@ static efi_status_t virt_efi_get_variable(efi_char16_t *name,
 					  unsigned long *data_size,
 					  void *data)
 {
-	return efi_call_virt(get_variable, name, vendor, attr, data_size, data);
+	unsigned long flags;
+	efi_status_t status;
+
+	spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(get_variable, name, vendor, attr, data_size,
+			       data);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static efi_status_t virt_efi_get_next_variable(unsigned long *name_size,
 					       efi_char16_t *name,
 					       efi_guid_t *vendor)
 {
-	return efi_call_virt(get_next_variable, name_size, name, vendor);
+	unsigned long flags;
+	efi_status_t status;
+
+	spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(get_next_variable, name_size, name, vendor);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static efi_status_t virt_efi_set_variable(efi_char16_t *name,
@@ -94,7 +187,17 @@ static efi_status_t virt_efi_set_variable(efi_char16_t *name,
 					  unsigned long data_size,
 					  void *data)
 {
-	return efi_call_virt(set_variable, name, vendor, attr, data_size, data);
+	unsigned long flags;
+	efi_status_t status;
+	bool __in_nmi = efi_in_nmi();
+
+	if (!__in_nmi)
+		spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(set_variable, name, vendor, attr, data_size,
+			       data);
+	if (!__in_nmi)
+		spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static efi_status_t virt_efi_query_variable_info(u32 attr,
@@ -102,16 +205,31 @@ static efi_status_t virt_efi_query_variable_info(u32 attr,
 						 u64 *remaining_space,
 						 u64 *max_variable_size)
 {
+	unsigned long flags;
+	efi_status_t status;
+	bool __in_nmi = efi_in_nmi();
+
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	return efi_call_virt(query_variable_info, attr, storage_space,
-			     remaining_space, max_variable_size);
+	if (!__in_nmi)
+		spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(query_variable_info, attr, storage_space,
+			       remaining_space, max_variable_size);
+	if (!__in_nmi)
+		spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static efi_status_t virt_efi_get_next_high_mono_count(u32 *count)
 {
-	return efi_call_virt(get_next_high_mono_count, count);
+	unsigned long flags;
+	efi_status_t status;
+
+	spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(get_next_high_mono_count, count);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static void virt_efi_reset_system(int reset_type,
@@ -119,17 +237,27 @@ static void virt_efi_reset_system(int reset_type,
 				  unsigned long data_size,
 				  efi_char16_t *data)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&efi_runtime_lock, flags);
 	__efi_call_virt(reset_system, reset_type, status, data_size, data);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
 }
 
 static efi_status_t virt_efi_update_capsule(efi_capsule_header_t **capsules,
 					    unsigned long count,
 					    unsigned long sg_list)
 {
+	unsigned long flags;
+	efi_status_t status;
+
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	return efi_call_virt(update_capsule, capsules, count, sg_list);
+	spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(update_capsule, capsules, count, sg_list);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 static efi_status_t virt_efi_query_capsule_caps(efi_capsule_header_t **capsules,
@@ -137,11 +265,17 @@ static efi_status_t virt_efi_query_capsule_caps(efi_capsule_header_t **capsules,
 						u64 *max_size,
 						int *reset_type)
 {
+	unsigned long flags;
+	efi_status_t status;
+
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
-	return efi_call_virt(query_capsule_caps, capsules, count, max_size,
-			     reset_type);
+	spin_lock_irqsave(&efi_runtime_lock, flags);
+	status = efi_call_virt(query_capsule_caps, capsules, count, max_size,
+			       reset_type);
+	spin_unlock_irqrestore(&efi_runtime_lock, flags);
+	return status;
 }
 
 void efi_native_runtime_setup(void)
-- 
1.8.3.2