linux-kernel - Re: [PATCH 2/2] powerpc/rtas: block error injection when locked down

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Message-ID: <CAHC9VhTWMFbCxQFAEJZzS3Kd5cSFigmvHac5y5ypVU7TqRqpTA@mail.gmail.com>
Date:   Thu, 22 Sep 2022 21:28:07 -0400
From:   Paul Moore <paul@...l-moore.com>
To:     Nathan Lynch <nathanl@...ux.ibm.com>
Cc:     linuxppc-dev@...ts.ozlabs.org,
        linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, jmorris@...ei.org,
        mpe@...erman.id.au, serge@...lyn.com, ajd@...ux.ibm.com,
        gcwilson@...ux.ibm.com, nayna@...ux.ibm.com
Subject: Re: [PATCH 2/2] powerpc/rtas: block error injection when locked down

On Thu, Sep 22, 2022 at 3:38 PM Nathan Lynch <nathanl@...ux.ibm.com> wrote:
>
> The error injection facility on pseries VMs allows corruption of
> arbitrary guest memory, potentially enabling a sufficiently privileged
> user to disable lockdown or perform other modifications of the running
> kernel via the rtas syscall.
>
> Block the PAPR error injection facility from being opened or called
> when locked down.
>
> Signed-off-by: Nathan Lynch <nathanl@...ux.ibm.com>
> ---
>  arch/powerpc/kernel/rtas.c | 25 ++++++++++++++++++++++++-
>  include/linux/security.h   |  1 +
>  security/security.c        |  1 +
>  3 files changed, 26 insertions(+), 1 deletion(-)

...

> diff --git a/include/linux/security.h b/include/linux/security.h
> index 1ca8dbacd3cc..b5d5138ae66a 100644
> --- a/include/linux/security.h
> +++ b/include/linux/security.h
> @@ -123,6 +123,7 @@ enum lockdown_reason {
>         LOCKDOWN_BPF_WRITE_USER,
>         LOCKDOWN_DBG_WRITE_KERNEL,
>         LOCKDOWN_DEVICE_TREE,
> +       LOCKDOWN_RTAS_ERROR_INJECTION,

With the understanding that I've never heard of RTAS until now, are
there any other RTAS events that would require a lockdown reason?  As
a follow up, is it important to distinguish between different RTAS
lockdown reasons?

I'm trying to determine if we can just call it LOCKDOWN_RTAS.

>         LOCKDOWN_INTEGRITY_MAX,
>         LOCKDOWN_KCORE,
>         LOCKDOWN_KPROBES,
> diff --git a/security/security.c b/security/security.c
> index 2863fc31eec6..6518b239ada2 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -61,6 +61,7 @@ const char *const lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
>         [LOCKDOWN_BPF_WRITE_USER] = "use of bpf to write user RAM",
>         [LOCKDOWN_DBG_WRITE_KERNEL] = "use of kgdb/kdb to write kernel RAM",
>         [LOCKDOWN_DEVICE_TREE] = "modifying device tree contents",
> +       [LOCKDOWN_RTAS_ERROR_INJECTION] = "RTAS error injection",

See above.

>         [LOCKDOWN_INTEGRITY_MAX] = "integrity",
>         [LOCKDOWN_KCORE] = "/proc/kcore access",
>         [LOCKDOWN_KPROBES] = "use of kprobes",
> --
> 2.37.3

-- 
paul-moore.com