efi/x86: Fix the deletion of variables in mixed mode

[ Upstream commit a4b81cc ]

efi_thunk_set_variable() treated the NULL "data" pointer as an invalid
parameter, and this broke the deletion of variables in mixed mode.
This commit fixes the check of data so that the userspace program can
delete a variable in mixed mode.

Fixes: 8319e9d ("efi/x86: Handle by-ref arguments covering multiple pages in mixed mode")
Signed-off-by: Gary Lin <glin@suse.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200408081606.1504-1-glin@suse.com
Link: https://lore.kernel.org/r/20200409130434.6736-9-ardb@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>

arch/x86/platform/efi/efi_64.c

@@ -641,7 +641,7 @@ efi_thunk_set_variable(efi_char16_t *name, efi_guid_t *vendor,
 	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_data = virt_to_phys_or_null_size(data, data_size);
 
-	if (!phys_name || !phys_data)
+	if (!phys_name || (data && !phys_data))
 		status = EFI_INVALID_PARAMETER;
 	else
 		status = efi_thunk(set_variable, phys_name, phys_vendor,
@@ -672,7 +672,7 @@ efi_thunk_set_variable_nonblocking(efi_char16_t *name, efi_guid_t *vendor,
 	phys_vendor = virt_to_phys_or_null(vnd);
 	phys_data = virt_to_phys_or_null_size(data, data_size);
 
-	if (!phys_name || !phys_data)
+	if (!phys_name || (data && !phys_data))
 		status = EFI_INVALID_PARAMETER;
 	else
 		status = efi_thunk(set_variable, phys_name, phys_vendor,