[PATCH v2 5/6] efi/runtime-wrappers: honour EFI_RUNTIME_SERVICES in the non-blocking paths

[Breno Leitao <leitao@debian.org>]

Three wrappers call firmware directly instead of going through
__efi_queue_work(), and none of them check whether runtime services are
still enabled: virt_efi_set_variable_nb(),
virt_efi_query_variable_info_nb() and virt_efi_reset_system(). Once a
hang has cleared EFI_RUNTIME_SERVICES - or efi_recover_from_page_fault()
has cleared it on a firmware page fault - these paths still enter the
(possibly wedged) firmware, e.g. an EFI pstore write through the
non-blocking SetVariable() variant, in violation of UEFI's
non-reentrancy rules. reset_system() is reachable too: efi_reboot()
only gates it on the static efi_rt_services_supported() mask, which does
not track the runtime disable.

Check efi_enabled(EFI_RUNTIME_SERVICES) at the top of each before taking
efi_runtime_lock and calling into firmware.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/firmware/efi/runtime-wrappers.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 8badf0419a148..842f72d44211f 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -461,6 +461,9 @@ virt_efi_set_variable_nb(efi_char16_t *name, efi_guid_t *vendor, u32 attr,
 {
 	efi_status_t status;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return EFI_DEVICE_ERROR;
+
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
@@ -500,6 +503,9 @@ virt_efi_query_variable_info_nb(u32 attr, u64 *storage_space,
 	if (efi.runtime_version < EFI_2_00_SYSTEM_TABLE_REVISION)
 		return EFI_UNSUPPORTED;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES))
+		return EFI_DEVICE_ERROR;
+
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
@@ -527,6 +533,11 @@ static void __nocfi
 virt_efi_reset_system(int reset_type, efi_status_t status,
 		      unsigned long data_size, efi_char16_t *data)
 {
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		pr_warn("EFI Runtime Services are disabled, not invoking reset_system()\n");
+		return;
+	}
+
 	if (down_trylock(&efi_runtime_lock)) {
 		pr_warn("failed to invoke the reset_system() runtime service:\n"
 			"could not get exclusive access to the firmware\n");

-- 
2.53.0-Meta