linux-kernel - Re: [PATCH] admin-guide/hw-vuln/core-scheduling: fix return type of PR_SCHED_CORE

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Message-ID: <c8b72a0a-93af-9024-1fec-5cd56b57a933@oracle.com>
Date: Tue, 23 Apr 2024 09:20:34 -0400
From: Chris Hyser <chris.hyser@...cle.com>
To: Thomas Weißschuh <linux@...ssschuh.net>,
        Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Josh Poimboeuf <jpoimboe@...nel.org>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Jonathan Corbet <corbet@....net>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Josh Don <joshdon@...gle.com>
Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH] admin-guide/hw-vuln/core-scheduling: fix return type of
 PR_SCHED_CORE_GET

On 4/23/24 06:34, Thomas Weißschuh wrote:

> sched_core_share_pid() copies the cookie to userspace with
> put_user(id, (u64 __user *)uaddr), expecting 64 bits of space.
> The "unsigned long" datatype that is documented in core-scheduling.rst
> however is only 32 bits large on 32 bit architectures.
>
> Document "unsigned long long" as the correct data type that is always
> 64bits large.
>
> This matches what the selftest cs_prctl_test.c has been doing all along.
>
> Fixes: 0159bb020ca9 ("Documentation: Add usecases, design and interface for core scheduling")
> Cc: stable@...r.kernel.org
> Link: https://lore.kernel.org/util-linux/df7a25a0-7923-4f8b-a527-5e6f0064074d@t-8ch.de/
> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
> ---
>   Documentation/admin-guide/hw-vuln/core-scheduling.rst | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/hw-vuln/core-scheduling.rst b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> index cf1eeefdfc32..a92e10ec402e 100644
> --- a/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> +++ b/Documentation/admin-guide/hw-vuln/core-scheduling.rst
> @@ -67,8 +67,8 @@ arg4:
>       will be performed for all tasks in the task group of ``pid``.
>   
>   arg5:
> -    userspace pointer to an unsigned long for storing the cookie returned by
> -    ``PR_SCHED_CORE_GET`` command. Should be 0 for all other commands.
> +    userspace pointer to an unsigned long long for storing the cookie returned
> +    by ``PR_SCHED_CORE_GET`` command. Should be 0 for all other commands.
>   


Yes you're right, that is what the test code actually does.


Reviewed-by: Chris Hyser <chris.hyser@...cle.com>


>   In order for a process to push a cookie to, or pull a cookie from a process, it
>   is required to have the ptrace access mode: `PTRACE_MODE_READ_REALCREDS` to the
>
> ---
> base-commit: 71b1543c83d65af8215d7558d70fc2ecbee77dcf
> change-id: 20240423-core-scheduling-cookie-b0551c40b086
>
> Best regards,