linux-kernel - Re: [PATCH v2] rseq: update kernel fields in lockstep with CONFIG_DEBUG

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Message-ID: <d61a3723-919d-40a7-a5ee-89f55bf8c445@efficios.com>
Date: Tue, 25 Feb 2025 15:04:24 -0500
From: Michael Jeanson <mjeanson@...icios.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 "Paul E. McKenney" <paulmck@...nel.org>, Boqun Feng <boqun.feng@...il.com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rseq: update kernel fields in lockstep with
 CONFIG_DEBUG_RSEQ

On 2025-02-25 14:56, Ingo Molnar wrote:
> 
> * Michael Jeanson <mjeanson@...icios.com> wrote:
> 
>> With CONFIG_DEBUG_RSEQ=y, an in-kernel copy of the read-only fields is
>> kept synchronized with the user-space fields. Ensure the updates are
>> done in lockstep in case we error out on a write to user-space.
>>
>> Fixes: 7d5265ffcd8b ("rseq: Validate read-only fields under DEBUG_RSEQ config")
>> Signed-off-by: Michael Jeanson <mjeanson@...icios.com>
>> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
>> ---
>>  kernel/rseq.c | 85 +++++++++++++++++++++++++++------------------------
>>  1 file changed, 45 insertions(+), 40 deletions(-)
>>
>> diff --git a/kernel/rseq.c b/kernel/rseq.c
>> index 2cb16091ec0a..88aa780f8cf4 100644
>> --- a/kernel/rseq.c
>> +++ b/kernel/rseq.c
>> @@ -26,6 +26,11 @@
>>  				  RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL | \
>>  				  RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE)
>>  
>> +static struct rseq __user *rseq_user_fields(struct task_struct *t)
>> +{
>> +	return (struct rseq __user *) t->rseq;
> 
> Why is this wrapper needed?
> 
> task_struct::rseq is already of that exact type AFAICS:
> 
>         struct rseq __user *rseq;

It's not needed, I can remove it and resend.

Thanks,

Michael