1 files changed, 25 insertions, 0 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;
+}