linux-kernel - Re: [PATCH v1 1/1] s390/uv: Panic if the security of the system cannot be guaranteed.

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Message-ID: <4d5d5368-88c1-4eff-b0fa-8b0e47957b89@linux.ibm.com>
Date: Fri, 2 Aug 2024 14:40:17 +0200
From: Steffen Eiden <seiden@...ux.ibm.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>, linux-kernel@...r.kernel.org
Cc: kvm@...r.kernel.org, linux-s390@...r.kernel.org, hca@...ux.ibm.com,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, borntraeger@...ibm.com,
        svens@...ux.ibm.com, frankja@...ux.ibm.com, nsg@...ux.ibm.com,
        nrb@...ux.ibm.com
Subject: Re: [PATCH v1 1/1] s390/uv: Panic if the security of the system
 cannot be guaranteed.



On 8/1/24 1:25 PM, Claudio Imbrenda wrote:
> The return value uv_set_shared() and uv_remove_shared() (which are
> wrappers around the share() function) is not always checked. The system
> integrity of a protected guest depends on the Share and Unshare UVCs
> being successful. This means that any caller that fails to check the
> return value will compromise the security of the protected guest.
> 
> No code path that would lead to such violation of the security
> guarantees is currently exercised, since all the areas that are shared
> never get unshared during the lifetime of the system. This might
> change and become an issue in the future.
> 
> The Share and Unshare UVCs can only fail in case of hypervisor
> misbehaviour (either a bug or malicious behaviour). In such cases there
> is no reasonable way forward, and the system needs to panic.
> 
> This patch replaces the return at the end of the share() function with
> a panic, to guarantee system integrity.
> 
> Fixes: 5abb9351dfd9 ("s390/uv: introduce guest side ultravisor code")
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@...ux.ibm.com>
> ---
>   arch/s390/include/asm/uv.h | 5 ++++-
>   1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/s390/include/asm/uv.h b/arch/s390/include/asm/uv.h
> index 0b5f8f3e84f1..153d93468b77 100644
> --- a/arch/s390/include/asm/uv.h
> +++ b/arch/s390/include/asm/uv.h
> @@ -441,7 +441,10 @@ static inline int share(unsigned long addr, u16 cmd)
>   
>   	if (!uv_call(0, (u64)&uvcb))
>   		return 0;
> -	return -EINVAL;
> +	pr_err("%s UVC failed (rc: 0x%x, rrc: 0x%x), possible hypervisor bug.\n",
> +	       uvcb.header.cmd == UVC_CMD_SET_SHARED_ACCESS ? "Share" : "Unshare",
> +	       uvcb.header.rc, uvcb.header.rrc);
> +	panic("System security cannot be guaranteed unless the system panics now.\n");
>   }
>   
>   /*