[PATCH v2] 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.

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.

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>
---
v2: check both at registration and at invocation time

 drivers/acpi/prmt.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/acpi/prmt.c b/drivers/acpi/prmt.c
index 998101cf16e47145..3d4c4620f9f95309 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_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,
-- 
2.39.0