ACPI: PRM: Check whether EFI runtime is available

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.

Given that the EFI runtime services may become unavailable after a crash
occurring in the firmware, we need to check this each time the PRM
address space handler is invoked. If the EFI runtime services were not
available at registration time to being with, don't install the address
space handler at all.

Fixes: cefc7ca ("ACPI: PRM: implement OperationRegion handler for the PlatformRtMechanism subtype")
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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_ratelimited("PRM: EFI runtime services no longer available\n");
+		return AE_NO_HANDLER;
+	}
+
 	/*
 	 * 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.
@@ -325,6 +330,11 @@ void __init init_prmt(void)
 
 	pr_info("PRM: found %u modules\n", mc);
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		pr_err("PRM: EFI runtime services unavailable\n");
+		return;
+	}
+
 	status = acpi_install_address_space_handler(ACPI_ROOT_OBJECT,
 						    ACPI_ADR_SPACE_PLATFORM_RT,
 						    &acpi_platformrt_space_handler,