linux-kernel - [PATCH] efi: fix userspace infinite retry read efivars after EFI runtime services page fault

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Date:   Tue, 27 Dec 2022 23:09:36 +0800
From:   Ding Hui <dinghui@...gfor.com.cn>
To:     ardb@...nel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     sai.praneeth.prakhya@...el.com, Ding Hui <dinghui@...gfor.com.cn>
Subject: [PATCH] efi: fix userspace infinite retry read efivars after EFI runtime services page fault

After [1][2], if we catch exceptions due to EFI runtime service, we will
clear EFI_RUNTIME_SERVICES bit to disable EFI runtime service, then the
subsequent routine which invoke the EFI runtime service should fail.

But the userspace cat efivars through /sys/firmware/efi/efivars/ will stuck
and infinite loop calling read() due to efivarfs_file_read() return -EINTR.

The -EINTR is converted from EFI_ABORTED by efi_status_to_err(), and is
an improper return value in this situation, so let virt_efi_xxx() return
EFI_DEVICE_ERROR and converted to -EIO to invoker.

[1]: commit 3425d934fc03 ("efi/x86: Handle page faults occurring while running EFI runtime services")
[2]: commit 23715a26c8d8 ("arm64: efi: Recover from synchronous exceptions occurring in firmware")

Signed-off-by: Ding Hui <dinghui@...gfor.com.cn>
---
 drivers/firmware/efi/runtime-wrappers.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
index 7feee3d9c2bf..1fba4e09cdcf 100644
--- a/drivers/firmware/efi/runtime-wrappers.c
+++ b/drivers/firmware/efi/runtime-wrappers.c
@@ -62,6 +62,7 @@ struct efi_runtime_work efi_rts_work;
 									\
 	if (!efi_enabled(EFI_RUNTIME_SERVICES)) {			\
 		pr_warn_once("EFI Runtime Services are disabled!\n");	\
+		efi_rts_work.status = EFI_DEVICE_ERROR;			\
 		goto exit;						\
 	}								\
 									\
-- 
2.17.1