efi: do not use runtime services table with efi=no-rs

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@zededa.com>
Fixes: dfcccc6631 "efi: use directmap to access runtime services table"
Signed-off-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Release-acked-by: Juergen Gross <jgross@suse.com>

diff --git a/xen/common/efi/runtime.c b/xen/common/efi/runtime.c
index 22fd6c9b53324b11742fd10853ecc948f1da7685..8c2ece468de97c7448b0ef0cad8b440de8cbae51 100644 (file)
--- a/xen/common/efi/runtime.c
+++ b/xen/common/efi/runtime.c
@@ -211,6 +211,8 @@ int efi_get_info(uint32_t idx, union xenpf_efi_info *info)
         break;
     case XEN_FW_EFI_RT_VERSION:
     {
+        if ( !efi_enabled(EFI_RS) )
+            return -EOPNOTSUPP;
         info->version = efi_rs->Hdr.Revision;
         break;
     }
@@ -613,7 +615,7 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
             break;
         }
 
-        if ( (efi_rs->Hdr.Revision >> 16) < 2 )
+        if ( !efi_enabled(EFI_RS) || (efi_rs->Hdr.Revision >> 16) < 2 )
             return -EOPNOTSUPP;
         state = efi_rs_enter();
         if ( !state.cr3 )
@@ -631,7 +633,7 @@ int efi_runtime_call(struct xenpf_efi_runtime_call *op)
         if ( op->misc )
             return -EINVAL;
 
-        if ( (efi_rs->Hdr.Revision >> 16) < 2 )
+        if ( !efi_enabled(EFI_RS) || (efi_rs->Hdr.Revision >> 16) < 2 )
             return -EOPNOTSUPP;
         /* XXX fall through for now */
     default: