x86, efivars: firmware bug workarounds should be in platform code

Let's not burden ia64 with checks in the common efivars code that we're not
writing too much data to the variable store. That kind of thing is an x86
firmware bug, plain and simple.

efi_query_variable_store() provides platforms with a wrapper in which they can
perform checks and workarounds for EFI variable storage bugs.

Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>

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;
+}