[PATCH v3 6/7] 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) in each before calling into
firmware. Test it after taking efi_runtime_lock rather than before: the
bit is only ever cleared at runtime while that lock is held, so checking
it under the lock avoids racing with a concurrent timeout that clears the
bit and drops the lock.

Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Breno Leitao <leitao@debian.org>
---
 drivers/firmware/efi/runtime-wrappers.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 2ec5cbdf46d07..2b0a7caf90944 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -480,6 +480,11 @@ virt_efi_set_variable_nb(efi_char16_t *name, efi_guid_t *vendor, u32 attr,
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		up(&efi_runtime_lock);
+		return EFI_DEVICE_ERROR;
+	}
+
 	efi_runtime_lock_owner = current;
 	status = efi_call_virt_pointer(efi.runtime, set_variable, name, vendor,
 				       attr, data_size, data);
@@ -519,6 +524,11 @@ virt_efi_query_variable_info_nb(u32 attr, u64 *storage_space,
 	if (down_trylock(&efi_runtime_lock))
 		return EFI_NOT_READY;
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		up(&efi_runtime_lock);
+		return EFI_DEVICE_ERROR;
+	}
+
 	efi_runtime_lock_owner = current;
 	status = efi_call_virt_pointer(efi.runtime, query_variable_info, attr,
 				       storage_space, remaining_space,
@@ -549,6 +559,12 @@ virt_efi_reset_system(int reset_type, efi_status_t status,
 		return;
 	}
 
+	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {
+		pr_warn("EFI Runtime Services are disabled, not invoking reset_system()\n");
+		up(&efi_runtime_lock);
+		return;
+	}
+
 	efi_runtime_lock_owner = current;
 	arch_efi_call_virt_setup();
 	efi_rts_work.efi_rts_id = EFI_RESET_SYSTEM;

-- 
2.53.0-Meta