[PATCH v4] efi: implement mandatory locking for UEFI Runtime Services
Ard Biesheuvel
ard.biesheuvel at linaro.org
Mon Aug 4 09:16:00 PDT 2014
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 at linaro.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
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