[PATCH] Fix: module signature vs tracepoints: add new TAINT_UNSIGNED_MODULE

Mathieu Desnoyers
2014-02-14T05:18:44Z

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>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@redhat.com>
CC: Thomas Gleixner <tglx@linutronix.de>
CC: Rusty Russell <rusty@rustcorp.com.au>
CC: David Howells <dhowells@redhat.com>
CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Documentation/ABI/testing/sysfs-module | 1 +
Documentation/module-signing.txt | 3 ++-
Documentation/oops-tracing.txt | 3 +++
Documentation/sysctl/kernel.txt | 2 ++
include/linux/kernel.h | 1 +
include/trace/events/module.h | 4 +++-
kernel/module.c | 4 +++-
kernel/panic.c | 2 ++
kernel/tracepoint.c | 5 +++--
9 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module
index 47064c2..b9a29cd 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 2b40e04..b6af42e 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 13032c0..879abe2 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 e55124e..8ebe1c0 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 196d1ea..4710900 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 1619327..11fd51b 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 d24fcf2..4d7d25e 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 6d63003..0e25fe1 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 29f2654..9bb887d 100644
--- a/kernel/tracepoint.c
+++ b/kernel/tracepoint.c
@@ -639,9 +639,10 @@ 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 (mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP)))
+ if (mod->taints & ~((1 << TAINT_OOT_MODULE) | (1 << TAINT_CRAP) |
+ (1 << TAINT_UNSIGNED_MODULE)))
return 0;
mutex_lock(&tracepoints_mutex);
tp_mod = kmalloc(sizeof(struct tp_module), GFP_KERNEL);
--
1.7.10.4