Fix: module signature vs tracepoints: add new TAINT_UNSIGNED_MODULE

Users have reported being unable to trace non-signed modules loaded
within a kernel supporting module signature.

This is caused by tracepoint.c:tracepoint_module_coming() refusing to
take into account tracepoints sitting within force-loaded modules
(TAINT_FORCED_MODULE). The reason for this check, in the first place, is
that a force-loaded module may have a struct module incompatible with
the layout expected by the kernel, and can thus cause a kernel crash
upon forced load of that module on a kernel with CONFIG_TRACEPOINTS=y.

Tracepoints, however, specifically accept TAINT_OOT_MODULE and
TAINT_CRAP, since those modules do not lead to the "very likely system
crash" issue cited above for force-loaded modules.

With kernels having CONFIG_MODULE_SIG=y (signed modules), a non-signed
module is tainted re-using the TAINT_FORCED_MODULE taint flag.
Unfortunately, this means that Tracepoints treat that module as a
force-loaded module, and thus silently refuse to consider any tracepoint
within this module.

Since an unsigned module does not fit within the "very likely system
crash" category of tainting, add a new TAINT_UNSIGNED_MODULE taint flag
to specifically address this taint behavior, and accept those modules
within Tracepoints. We use the letter 'X' as a taint flag character for
a module being loaded that doesn't know how to sign its name (proposed
by Steven Rostedt).

Also add the missing 'O' entry to trace event show_module_flags() list
for the sake of completeness.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Steven Rostedt <rostedt@goodmis.org>
NAKed-by: Ingo Molnar <mingo@redhat.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: David Howells <dhowells@redhat.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

9 files changed, 20 insertions, 5 deletions

diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module
index 47064c2b1f79..b9a29cdbaccb 100644
--- a/Documentation/ABI/testing/sysfs-module
+++ b/Documentation/ABI/testing/sysfs-module
@@ -49,3 +49,4 @@ Description:	Module taint flags:
                         O - out-of-tree module
                         F - force-loaded module
                         C - staging driver module
+                        X - unsigned module
diff --git a/Documentation/module-signing.txt b/Documentation/module-signing.txt
index 2b40e04d3c49..b6af42e4d790 100644
--- a/Documentation/module-signing.txt
+++ b/Documentation/module-signing.txt
@@ -53,7 +53,8 @@ This has a number of options available:
 
      If this is off (ie. "permissive"), then modules for which the key is not
      available and modules that are unsigned are permitted, but the kernel will
-     be marked as being tainted.
+     be marked as being tainted, and the concerned modules will be marked as
+     tainted, shown with the character 'X'.
 
      If this is on (ie. "restrictive"), only modules that have a valid
      signature that can be verified by a public key in the kernel's possession
diff --git a/Documentation/oops-tracing.txt b/Documentation/oops-tracing.txt
index 13032c0140d4..879abe289523 100644
--- a/Documentation/oops-tracing.txt
+++ b/Documentation/oops-tracing.txt
@@ -265,6 +265,9 @@ characters, each representing a particular tainted value.
 
  13: 'O' if an externally-built ("out-of-tree") module has been loaded.
 
+ 14: 'X' if an unsigned module has been loaded in a kernel supporting
+     module signature.
+
 The primary reason for the 'Tainted: ' string is to tell kernel
 debuggers if this is a clean kernel or if anything unusual has
 occurred.  Tainting is permanent: even if an offending module is
diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
index e55124e7c40c..8ebe1c047004 100644
--- a/Documentation/sysctl/kernel.txt
+++ b/Documentation/sysctl/kernel.txt
@@ -792,6 +792,8 @@ can be ORed together:
 1024 - A module from drivers/staging was loaded.
 2048 - The system is working around a severe firmware bug.
 4096 - An out-of-tree module has been loaded.
+8192 - An unsigned module has been loaded in a kernel supporting module
+       signature.
 
 ==============================================================
 
diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 196d1ea86df0..471090093c67 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h
@@ -469,6 +469,7 @@ extern enum system_states {
 #define TAINT_CRAP                      10
 #define TAINT_FIRMWARE_WORKAROUND       11
 #define TAINT_OOT_MODULE                12
+#define TAINT_UNSIGNED_MODULE           13
 
 extern const char hex_asc[];
 #define hex_asc_lo(x)   hex_asc[((x) & 0x0f)]
diff --git a/include/trace/events/module.h b/include/trace/events/module.h
index 161932737416..11fd51b413de 100644
--- a/include/trace/events/module.h
+++ b/include/trace/events/module.h
@@ -22,8 +22,10 @@ struct module;
 
 #define show_module_flags(flags) __print_flags(flags, "",       \
         { (1UL << TAINT_PROPRIETARY_MODULE),    "P" },          \
+        { (1UL << TAINT_OOT_MODULE),            "O" },          \
         { (1UL << TAINT_FORCED_MODULE),         "F" },          \
-        { (1UL << TAINT_CRAP),                  "C" })
+        { (1UL << TAINT_CRAP),                  "C" },          \
+        { (1UL << TAINT_UNSIGNED_MODULE),       "X" })
 
 TRACE_EVENT(module_load,
 
diff --git a/kernel/module.c b/kernel/module.c
index efa1e6031950..c1acb0c5b637 100644
--- a/kernel/module.c
+++ b/kernel/module.c
@@ -1013,6 +1013,8 @@ static size_t module_flags_taint(struct module *mod, char *buf)
                 buf[l++] = 'F';
         if (mod->taints & (1 << TAINT_CRAP))
                 buf[l++] = 'C';
+        if (mod->taints & (1 << TAINT_UNSIGNED_MODULE))
+                buf[l++] = 'X';
         /*
          * TAINT_FORCED_RMMOD: could be added.
          * TAINT_UNSAFE_SMP, TAINT_MACHINE_CHECK, TAINT_BAD_PAGE don't
@@ -3214,7 +3216,7 @@ static int load_module(struct load_info *info, const char __user *uargs,
                 pr_notice_once("%s: module verification failed: signature "
                                "and/or  required key missing - tainting "
                                "kernel\n", mod->name);
-                add_taint_module(mod, TAINT_FORCED_MODULE, LOCKDEP_STILL_OK);
+                add_taint_module(mod, TAINT_UNSIGNED_MODULE, LOCKDEP_STILL_OK);
         }
 #endif
 
diff --git a/kernel/panic.c b/kernel/panic.c
index 6d6300375090..0e25fe10871e 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -210,6 +210,7 @@ static const struct tnt tnts[] = {
         { TAINT_CRAP,                   'C', ' ' },
         { TAINT_FIRMWARE_WORKAROUND,    'I', ' ' },
         { TAINT_OOT_MODULE,             'O', ' ' },
+        { TAINT_UNSIGNED_MODULE,        'X', ' ' },
 };
 
 /**
@@ -228,6 +229,7 @@ static const struct tnt tnts[] = {
  *  'C' - modules from drivers/staging are loaded.
  *  'I' - Working around severe firmware bug.
  *  'O' - Out-of-tree module has been loaded.
+ *  'X' - Unsigned module has been loaded.
  *
  *      The string is overwritten by the next call to print_tainted().
  */
diff --git a/kernel/tracepoint.c b/kernel/tracepoint.c
index 031cc5655a51..3cdbed1fbdc7 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -633,7 +633,8 @@ EXPORT_SYMBOL_GPL(tracepoint_iter_reset);
 #ifdef CONFIG_MODULES
 bool trace_module_has_bad_taint(struct module *mod)
 {
-        return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP));
+        return mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
+                               (1 << TAINT_UNSIGNED_MODULE));
 }
 
 static int tracepoint_module_coming(struct module *mod)
@@ -644,7 +645,7 @@ static int tracepoint_module_coming(struct module *mod)
         /*
          * We skip modules that taint the kernel, especially those with different
          * module headers (for forced load), to make sure we don't cause a crash.
-         * Staging and out-of-tree GPL modules are fine.
+         * Staging, out-of-tree, and unsigned GPL modules are fine.
          */
         if (trace_module_has_bad_taint(mod))
                 return 0;