linux-kernel - Re: [PATCH v2 1/9] s390/uaccess: Add storage key checked cmpxchg access to user space

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Date:   Thu, 20 Oct 2022 13:18:37 +0200
From:   Heiko Carstens <hca@...ux.ibm.com>
To:     Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@...ux.ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>,
        Jonathan Corbet <corbet@....net>, kvm@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-s390@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        Sven Schnelle <svens@...ux.ibm.com>
Subject: Re: [PATCH v2 1/9] s390/uaccess: Add storage key checked cmpxchg
 access to user space

Hi Janis,

On Wed, Oct 12, 2022 at 10:56:01PM +0200, Janis Schoetterl-Glausch wrote:
> Add cmpxchg functionality similar to that in cmpxchg.h except that the
> target is a user space address and that the address' storage key is
> matched with the access_key argument in order to honor key-controlled
> protection.
> The access is performed by changing to the secondary-spaces mode and
> setting the PSW key for the duration of the compare and swap.
> 
> Signed-off-by: Janis Schoetterl-Glausch <scgl@...ux.ibm.com>
> ---
> 
> 
> Possible variations:
>   * check the assumptions made in cmpxchg_user_key_size and error out
>   * call functions called by copy_to_user
>      * access_ok? is a nop
>      * should_fail_usercopy?
>      * instrument_copy_to_user? doesn't make sense IMO
>   * don't be overly strict in cmpxchg_user_key
> 
> 
>  arch/s390/include/asm/uaccess.h | 189 ++++++++++++++++++++++++++++++++
>  1 file changed, 189 insertions(+)

This not how I would have expected something that would be
symmetrical/consistent with what we already have. However instead of
spending several iterations I'll send something for this.

This might take a bit due to my limited time. So please be patient.