[Xen-devel] [PATCH v2] xsm: hide detailed Xen version from unprivileged guests

[Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>]

Hide the following information that can help identify the running Xen
binary version: XENVER_extraversion, XENVER_compile_info, XENVER_changeset.
Add explicit cases for XENVER_commandline and XENVER_build_id as well.

Introduce xsm_filter_denied() to hvmloader to remove "<denied>" string
from guest's DMI tables that otherwise would be shown in tools like
dmidecode.

Signed-off-by: Sergey Dyasli <sergey.dyasli@xxxxxxxxxx>
---
v1 --> v2:
- Added xsm_filter_denied() to hvmloader instead of modifying xen_deny()
- Made behaviour the same for both Release and Debug builds
- XENVER_capabilities is no longer hided

CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: George Dunlap <George.Dunlap@xxxxxxxxxxxxx>
CC: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Jan Beulich <jbeulich@xxxxxxxx>
CC: Julien Grall <julien@xxxxxxx>
CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
CC: Daniel De Graaf <dgdegra@xxxxxxxxxxxxx>
---
 tools/firmware/hvmloader/hvmloader.c | 1 +
 tools/firmware/hvmloader/smbios.c    | 1 +
 tools/firmware/hvmloader/util.c      | 6 ++++++
 tools/firmware/hvmloader/util.h      | 2 ++
 xen/include/xsm/dummy.h              | 9 ++++++---
 5 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/tools/firmware/hvmloader/hvmloader.c 
b/tools/firmware/hvmloader/hvmloader.c
index 598a226278..e760ed5fa6 100644
--- a/tools/firmware/hvmloader/hvmloader.c
+++ b/tools/firmware/hvmloader/hvmloader.c
@@ -147,6 +147,7 @@ static void init_hypercalls(void)
     /* Print version information. */
     cpuid(base + 1, &eax, &ebx, &ecx, &edx);
     hypercall_xen_version(XENVER_extraversion, extraversion);
+    xsm_filter_denied(extraversion, sizeof(extraversion));
     printf("Detected Xen v%u.%u%s\n", eax >> 16, eax & 0xffff, extraversion);
 }
 
diff --git a/tools/firmware/hvmloader/smbios.c 
b/tools/firmware/hvmloader/smbios.c
index 97a054e9e3..1ba352ed2c 100644
--- a/tools/firmware/hvmloader/smbios.c
+++ b/tools/firmware/hvmloader/smbios.c
@@ -275,6 +275,7 @@ hvm_write_smbios_tables(
     xen_minor_version = (uint16_t) xen_version;
 
     hypercall_xen_version(XENVER_extraversion, xen_extra_version);
+    xsm_filter_denied(xen_extra_version, sizeof(xen_extra_version));
 
     /* build up human-readable Xen version string */
     p = xen_version_str;
diff --git a/tools/firmware/hvmloader/util.c b/tools/firmware/hvmloader/util.c
index 0c3f2d24cd..09e355fa3d 100644
--- a/tools/firmware/hvmloader/util.c
+++ b/tools/firmware/hvmloader/util.c
@@ -995,6 +995,12 @@ void hvmloader_acpi_build_tables(struct acpi_config 
*config,
     hvm_param_set(HVM_PARAM_VM_GENERATION_ID_ADDR, config->vm_gid_addr);
 }
 
+void xsm_filter_denied(char *str, size_t len)
+{
+    if ( strcmp(str, "<denied>") == 0 )
+        memset(str, 0, len);
+}
+
 /*
  * Local variables:
  * mode: C
diff --git a/tools/firmware/hvmloader/util.h b/tools/firmware/hvmloader/util.h
index 7bca6418d2..f7d907ca00 100644
--- a/tools/firmware/hvmloader/util.h
+++ b/tools/firmware/hvmloader/util.h
@@ -286,6 +286,8 @@ struct acpi_config;
 void hvmloader_acpi_build_tables(struct acpi_config *config,
                                  unsigned int physical);
 
+void xsm_filter_denied(char *str, size_t len);
+
 #endif /* __HVMLOADER_UTIL_H__ */
 
 /*
diff --git a/xen/include/xsm/dummy.h b/xen/include/xsm/dummy.h
index b8e185e6fa..d15b078f10 100644
--- a/xen/include/xsm/dummy.h
+++ b/xen/include/xsm/dummy.h
@@ -750,14 +750,17 @@ static XSM_INLINE int xsm_xen_version (XSM_DEFAULT_ARG 
uint32_t op)
     case XENVER_get_features:
         /* These sub-ops ignore the permission checks and return data. */
         return 0;
-    case XENVER_extraversion:
-    case XENVER_compile_info:
     case XENVER_capabilities:
-    case XENVER_changeset:
     case XENVER_pagesize:
     case XENVER_guest_handle:
         /* These MUST always be accessible to any guest by default. */
         return xsm_default_action(XSM_HOOK, current->domain, NULL);
+
+    case XENVER_extraversion:
+    case XENVER_compile_info:
+    case XENVER_changeset:
+    case XENVER_commandline:
+    case XENVER_build_id:
     default:
         return xsm_default_action(XSM_PRIV, current->domain, NULL);
     }
-- 
2.17.1


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