[Xen-devel] [PATCH v4 1/2] xsm: add Kconfig option for denied string

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Add Kconfig option to make it possible to configure the string returned
to non-privileged guests instead of the default "<denied>" which could
propagate to UI / logs after the subsequent patch that hides detailed
Xen version information from unprivileged guests.

Introduce XENVER_denied_string to allow guests to set up UI / logs
filtering which dependens on the new CONFIG_XSM_DENIED_STRING.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v3 --> v4:
- Updated kconfig prompt description
- Added XENVER_denied_string
- Added #ifdef to fix build when CONFIG_XSM is not set

v2 --> v3:
- new patch

---
 xen/common/Kconfig           |  8 ++++++++
 xen/common/kernel.c          | 11 +++++++++++
 xen/common/version.c         |  4 ++++
 xen/include/public/version.h |  5 +++++
 xen/include/xsm/dummy.h      |  1 +
 5 files changed, 29 insertions(+)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index a6914fcae9..4a1a9398cd 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -228,6 +228,14 @@ choice
                bool "SILO" if XSM_SILO
 endchoice
 
+config XSM_DENIED_STRING
+       string "xen_version hypercall denied information replacement string"
+       default "<denied>"
+       depends on XSM
+       ---help---
+         A string which substitutes sensitive information returned via
+         xen_version hypercall to non-privileged guests
+
 config LATE_HWDOM
        bool "Dedicated hardware domain"
        default n
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 22941cec94..1c22e5d167 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -561,6 +561,17 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
 
         return sz;
     }
+
+    case XENVER_denied_string:
+    {
+        xen_denied_string_t str;
+
+        safe_strcpy(str, xen_deny());
+        if ( copy_to_guest(arg, str, XEN_DENIED_STRING_LEN) )
+            return -EFAULT;
+
+        return 0;
+    }
     }
 
     return -ENOSYS;
diff --git a/xen/common/version.c b/xen/common/version.c
index 937eb1281c..fbd0ef4668 100644
--- a/xen/common/version.c
+++ b/xen/common/version.c
@@ -67,7 +67,11 @@ const char *xen_banner(void)
 
 const char *xen_deny(void)
 {
+#ifdef CONFIG_XSM_DENIED_STRING
+    return CONFIG_XSM_DENIED_STRING;
+#else
     return "<denied>";
+#endif
 }
 
 static const void *build_id_p __read_mostly;
diff --git a/xen/include/public/version.h b/xen/include/public/version.h
index 17a81e23cd..f65001d2d9 100644
--- a/xen/include/public/version.h
+++ b/xen/include/public/version.h
@@ -100,6 +100,11 @@ struct xen_build_id {
 };
 typedef struct xen_build_id xen_build_id_t;
 
+/* arg == xen_denied_string_t. */
+#define XENVER_denied_string 11
+typedef char xen_denied_string_t[64];
+#define XEN_DENIED_STRING_LEN (sizeof(xen_denied_string_t))
+
 #endif /* __XEN_PUBLIC_VERSION_H__ */
 
 /*
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index b8e185e6fa..72a101b106 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -748,6 +748,7 @@ static XSM_INLINE int xsm_xen_version (XSM_DEFAULT_ARG 
uint32_t op)
     case XENVER_version:
     case XENVER_platform_parameters:
     case XENVER_get_features:
+    case XENVER_denied_string:
         /* These sub-ops ignore the permission checks and return data. */
         return 0;
     case XENVER_extraversion:
-- 
2.17.1


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