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

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Message-ID: <CAMj1kXFFA0SVa1_Zw+jT4Tqm2XynutN=T9BjaDxfaSR-ataoUg@mail.gmail.com>
Date:   Mon, 2 Jan 2023 11:49:46 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Ding Hui <dinghui@...gfor.com.cn>
Cc:     linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
        sai.praneeth.prakhya@...el.com
Subject: Re: [PATCH] efi: fix userspace infinite retry read efivars after EFI
 runtime services page fault

On Tue, 27 Dec 2022 at 16:18, Ding Hui <dinghui@...gfor.com.cn> wrote:
>
> 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>

Thanks for the fix, queued up in efi/urgent now.

> ---
>  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
>