3 files changed, 36 insertions, 16 deletions

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 5f2ecaf3f9d8..c89c245eff40 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -999,3 +999,28 @@ u64 efi_mem_attributes(unsigned long phys_addr)
         }
         return 0;
 }
+
+/*
+ * Some firmware has serious problems when using more than 50% of the EFI
+ * variable store, i.e. it triggers bugs that can brick machines. Ensure that
+ * we never use more than this safe limit.
+ *
+ * Return EFI_SUCCESS if it is safe to write 'size' bytes to the variable
+ * store.
+ */
+efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
+{
+        efi_status_t status;
+        u64 storage_size, remaining_size, max_size;
+
+        status = efi.query_variable_info(attributes, &storage_size,
+                                         &remaining_size, &max_size);
+        if (status != EFI_SUCCESS)
+                return status;
+
+        if (!storage_size || size > remaining_size || size > max_size ||
+            (remaining_size - size) < (storage_size / 2))
+                return EFI_OUT_OF_RESOURCES;
+
+        return EFI_SUCCESS;
+}
diff --git a/drivers/firmware/efivars.c b/drivers/firmware/efivars.c
index 7acafb80fd4c..bf15d81d74e1 100644
--- a/drivers/firmware/efivars.c
+++ b/drivers/firmware/efivars.c
@@ -436,24 +436,12 @@ static efi_status_t
 check_var_size_locked(struct efivars *efivars, u32 attributes,
                         unsigned long size)
 {
-        u64 storage_size, remaining_size, max_size;
-        efi_status_t status;
         const struct efivar_operations *fops = efivars->ops;
 
-        if (!efivars->ops->query_variable_info)
+        if (!efivars->ops->query_variable_store)
                 return EFI_UNSUPPORTED;
 
-        status = fops->query_variable_info(attributes, &storage_size,
-                                           &remaining_size, &max_size);
-
-        if (status != EFI_SUCCESS)
-                return status;
-
-        if (!storage_size || size > remaining_size || size > max_size ||
-            (remaining_size - size) < (storage_size / 2))
-                return EFI_OUT_OF_RESOURCES;
-
-        return status;
+        return fops->query_variable_store(attributes, size);
 }
 
 
@@ -2131,7 +2119,7 @@ efivars_init(void)
         ops.get_variable = efi.get_variable;
         ops.set_variable = efi.set_variable;
         ops.get_next_variable = efi.get_next_variable;
-        ops.query_variable_info = efi.query_variable_info;
+        ops.query_variable_store = efi_query_variable_store;
 
         error = register_efivars(&__efivars, &ops, efi_kobj);
         if (error)
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 9bf2f1fcae27..3d7df3d32c66 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -333,6 +333,7 @@ typedef efi_status_t efi_query_capsule_caps_t(efi_capsule_header_t **capsules,
                                               unsigned long count,
                                               u64 *max_size,
                                               int *reset_type);
+typedef efi_status_t efi_query_variable_store_t(u32 attributes, unsigned long size);
 
 /*
  *  EFI Configuration Table and GUID definitions
@@ -575,9 +576,15 @@ extern void efi_enter_virtual_mode (void);	/* switch EFI to virtual mode, if pos
 #ifdef CONFIG_X86
 extern void efi_late_init(void);
 extern void efi_free_boot_services(void);
+extern efi_status_t efi_query_variable_store(u32 attributes, unsigned long size);
 #else
 static inline void efi_late_init(void) {}
 static inline void efi_free_boot_services(void) {}
+
+static inline efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
+{
+        return EFI_SUCCESS;
+}
 #endif
 extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 extern u64 efi_get_iobase (void);
@@ -731,7 +738,7 @@ struct efivar_operations {
         efi_get_variable_t *get_variable;
         efi_get_next_variable_t *get_next_variable;
         efi_set_variable_t *set_variable;
-        efi_query_variable_info_t *query_variable_info;
+        efi_query_variable_store_t *query_variable_store;
 };
 
 struct efivars {