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

Steffen Eiden
2024-08-02T12:40:25Z

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@linux.ibm.com>
Reviewed-by: Steffen Eiden <seiden@linux.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");
> }
>
> /*