[RFC] Add "GELI Passphrase:" prompt to boot loader
Devin Teske
dteske at FreeBSD.org
Mon Apr 6 17:39:46 UTC 2015
> On Apr 6, 2015, at 10:24 AM, Eric van Gyzen <eric at vangyzen.net> wrote:
>
> On 04/06/2015 12:58, Devin Teske wrote:
>> Hi -current,
>>
>> I have a pending enhancement to the boot loader that Colin P. and I
>> have been working on together.
>>
>> URL: https://reviews.freebsd.org/D2105 <https://reviews.freebsd.org/D2105>
>>
>> The nature of the patch is to cause the boot loader to prompt for the
>> GELI passphrase and then pass that on (through a kenv(1) variable)
>> to Colin’s code in geom_eli.ko where it will be:
>>
>> (a) picked up for-use as the initial passphrase attempt(s)
>> (b) zeroed after being picked-up so “kenv kern.geom.eli.passphrase”
>> returns nothing
>>
>> NB: Actually, “kenv kern.geom.eli.passphrase” generates the error
>> “kenv: unable to get kern.geom.eli.passphrase”
>>
>> The problem that I (we) need help in solving is:
>>
>> If the geom_eli.ko module doesn’t get loaded, then the variable
>> (kern.geom.eli.passphrase) is not zeroed.
>>
>> While I do think that this is of minimal concern (not loading the GELI
>> module means you won’t be able to get past the mountroot prompt in
>> the case where GELI is required to boot), I discussed with Colin and
>> I think we are in consensus that the resetting of the variable should
>> perhaps be moved to another section of the kernel to prevent leakage
>> of this sensitive information being passed through kenv(1) variable(s).
>>
>> Issue for me is, I’m not sure where the best place to move this to.
>> Here’s the code that needs to be moved (Lines 108-109 of g_eli.c):
>>
>> https://svnweb.freebsd.org/base?view=revision&revision=273489 <https://svnweb.freebsd.org/base?view=revision&revision=273489>
>>
>>
>> 108 <https://svnweb.freebsd.org/base/head/sys/geom/eli/g_eli.c?annotate=273489&pathrev=273489#l108> /* Wipe the passphrase from the environment. */
>> 109 <https://svnweb.freebsd.org/base/head/sys/geom/eli/g_eli.c?annotate=273489&pathrev=273489#l109> kern_unsetenv("kern.geom.eli.passphrase");
>>
>> Need to move that preferably to some place in the kernel that is NOT
>> optional in the compilation process. Suggestions?
>
> How about putting it right after a successful mount of the root file system?
> (I've never used GELI, so this could be as "right out" as five.)
>
I think that’s an excellent idea.
/me rummages through source
I’m thinking that the best place might be where we deal with the registered
event handler for mountroot.
One place that I crawled upon that looks particularly sexy is in start_init()
of sys/kern/init_main.c:
### BEGIN SNIPPET ###
/*
* Start the initial user process; try exec’ing each pathname in init_path.
* The program is invoked with one argument containing the boot flags.
*/
static void
start_init(void *dummy)
{
vm_offset_t addr;
struct execve_args args;
int options, error;
char *var, *path, *next, *s;
char *ucp, **uap, *arg0, *arg1;
struct thread *td;
struct proc *p;
mtx_lock(&Giant);
GIANT_REQUIRED;
td = furthered;
p = td->td_proc;
vfs_mountroot();
### RFC for code placement ###
/* XXX Put reset of kern.geom.eli.passphrase here XXX */
##########################
/*
* Need just enough stack to hold the faked-up “execve()” arguments.
*/
// snip rest //
### END SNIPPET ###
Or can you think of a better place?
—
Devin
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