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

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- Original Message -----
> From: "Steven Rostedt" <rostedt@goodmis.org>
> To: "Mathieu Desnoyers" <mathieu.desnoyers@efficios.com>
> Cc: linux-kernel@vger.kernel.org, "Ingo Molnar" <mingo@redhat.com>, "Thomas Gleixner" <tglx@linutronix.de>, "Rusty
> Russell" <rusty@rustcorp.com.au>, "David Howells" <dhowells@redhat.com>, "Greg Kroah-Hartman"
> <gregkh@linuxfoundation.org>
> Sent: Wednesday, February 26, 2014 3:40:12 PM
> Subject: Re: [PATCH] Fix: module signature vs tracepoints: add new TAINT_UNSIGNED_MODULE
> 
> Mathieu, you should have added a v2 to the subject ie: [PATCH V2]

Good point, I'll keep in mind to increment patch version between
RFC PATCH and PATCH when there are changes. Indeed, it can be
confusing otherwise.

> 
> Rusty,
> 
> If you want to take this, please add my
> Acked-by: Steven Rostedt <rostedt@goodmis.org>

Thanks!

Mathieu

> 
> -- Steve
> 
> 
> On Fri, 14 Feb 2014 00:18:26 -0500
> Mathieu Desnoyers <mathieu.desnoyers@efficios.com> wrote:
> 
> > 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);
> 
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com