linux-kernel - Re: [PATCH V4 2/2] blktrace: allow access trace file in lockdown mode

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Date:   Tue, 25 Apr 2023 10:55:46 -0700
From:   Junxiao Bi <junxiao.bi@...cle.com>
To:     linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-block@...r.kernel.org
Cc:     paul@...l-moore.com, nathanl@...ux.ibm.com, axboe@...nel.dk,
        jmorris@...ei.org, serge@...lyn.com, konrad.wilk@...cle.com,
        joe.jin@...cle.com
Subject: Re: [PATCH V4 2/2] blktrace: allow access trace file in lockdown mode

Any IO folks can help review this patch?

Paul needs a confirm from you that the information blktrace exporting to 
userspace through the relay files are safe, not leaking information that 
userspace shouldn't know in lockdown mode.

Thanks,

Junxiao.

On 4/20/23 2:53 PM, Junxiao Bi wrote:
> blktrace trace files are per-cpu relay files that are used by kernel to
> export IO metadata(IO events, type, target disk, offset and len etc.) to
> userspace, no data from IO itself will be exported. Bypass lockdown for
> these files will make blktrace work in lockdown mode.
>
> Signed-off-by: Junxiao Bi <junxiao.bi@...cle.com>
> ---
>   kernel/trace/blktrace.c | 6 ++++++
>   1 file changed, 6 insertions(+)
>
> diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c
> index d5d94510afd3..e1a9f8b7d710 100644
> --- a/kernel/trace/blktrace.c
> +++ b/kernel/trace/blktrace.c
> @@ -490,10 +490,16 @@ static struct dentry *blk_create_buf_file_callback(const char *filename,
>   					&relay_file_operations);
>   }
>   
> +static bool blk_bypass_lockdown(struct inode *inode)
> +{
> +	return true;
> +}
> +
>   static const struct rchan_callbacks blk_relay_callbacks = {
>   	.subbuf_start		= blk_subbuf_start_callback,
>   	.create_buf_file	= blk_create_buf_file_callback,
>   	.remove_buf_file	= blk_remove_buf_file_callback,
> +	.bypass_lockdown	= blk_bypass_lockdown,
>   };
>   
>   static void blk_trace_setup_lba(struct blk_trace *bt,