[PATCH] ACPI: PRM: Check whether EFI runtime is available

[Ard Biesheuvel <ardb@kernel.org>]

The ACPI PRM address space handler calls efi_call_virt_pointer() to
execute PRM firmware code, but doing so is only permitted when the EFI
runtime environment is available. Otherwise, such calls are guaranteed
to result in a crash, and must therefore be avoided.

Cc: <stable@vger.kernel.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Len Brown <lenb@kernel.org>
Cc: linux-acpi@vger.kernel.org
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/acpi/prmt.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/acpi/prmt.c b/drivers/acpi/prmt.c
index 998101cf16e47145..74f924077866ae69 100644
--- a/drivers/acpi/prmt.c
+++ b/drivers/acpi/prmt.c
@@ -236,6 +236,11 @@ static acpi_status acpi_platformrt_space_handler(u32 function,
 	efi_status_t status;
 	struct prm_context_buffer context;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		pr_err("PRM: EFI runtime services unavailable\n");
+		return AE_NOT_IMPLEMENTED;
+	}
+
 	/*
 	 * The returned acpi_status will always be AE_OK. Error values will be
 	 * saved in the first byte of the PRM message buffer to be used by ASL.
-- 
2.39.0