Re: [Xen-devel] [PATCH for-4.13] efi: do not use runtime services table with efi=no-rs

[Jan Beulich <jbeulich@xxxxxxxx>]

On 17.11.2019 00:47, Marek Marczykowski-Górecki  wrote:
> Before dfcccc6631 "efi: use directmap to access runtime services table"
> all usages of efi_rs pointer were guarded by efi_rs_enter(), which
> implicitly refused to operate with efi=no-rs (by checking if
> efi_l4_pgtable is NULL - which is the case for efi=no-rs). The said
> commit (re)moved that call as unneeded for just reading content of
> efi_rs structure - to avoid unnecessary page tables switch. But it
> neglected to check if efi_rs access is legal.
> 
> Fix this by adding explicit check for runtime service being enabled in
> the cases that do not use efi_rs_enter().
> 
> Reported-by: Roman Shaposhnik <roman@xxxxxxxxxx>
> Fixes: dfcccc6631 "efi: use directmap to access runtime services table"
> Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Albeit I would have preferred ...

> @@ -613,6 +615,8 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
>              break;
>          }
>  
> +        if ( !efi_enabled(EFI_RS) )
> +            return -EOPNOTSUPP;
>          if ( (efi_rs->Hdr.Revision >> 16) < 2 )
>              return -EOPNOTSUPP;
>          state = efi_rs_enter();
> @@ -631,6 +635,8 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
>          if ( op->misc )
>              return -EINVAL;
>  
> +        if ( !efi_enabled(EFI_RS) )
> +            return -EOPNOTSUPP;
>          if ( (efi_rs->Hdr.Revision >> 16) < 2 )
>              return -EOPNOTSUPP;

... if these two pairs of if()-s would each have been folded; I may
take the liberty to do so while committing if I end up being the
committer of this.

Jan

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