On Wed, May 02, 2018 at 09:57:57PM -0700, Kees Cook wrote: > On Wed, May 2, 2018 at 3:50 PM, Tobin C. Harding <[email protected]> wrote: > > Currently printing [hashed] pointers requires either a hw RNG or enough > > entropy to be available. Early in the boot sequence these conditions > > may not be met resulting in a dummy string '(____ptrval____)' being > > printed. This makes debugging the early boot sequence difficult. We > > can relax the requirement to use cryptographically secure hashing during > > debugging. This enables debugging while keeping development/production > > kernel behaviour the same. > > > > If new command line option debug_early_boot is enabled use > > cryptographically insecure hashing and hash pointer value immediately. > > > > Signed-off-by: Tobin C. Harding <[email protected]> > > --- > > Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++ > > lib/vsprintf.c | 18 ++++++++++++++++++ > > 2 files changed, 26 insertions(+) > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt > > b/Documentation/admin-guide/kernel-parameters.txt > > index b8d1379aa039..ab619c4ccbf2 100644 > > --- a/Documentation/admin-guide/kernel-parameters.txt > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > @@ -748,6 +748,14 @@ > > > > debug [KNL] Enable kernel debugging (events log level). > > > > + debug_early_boot > > + [KNL] Enable debugging early in the boot sequence. > > If > > + enabled, we use a weak hash instead of siphash to > > hash > > + pointers. Use this option if you need to see > > pointer > > + values during early boot (i.e you are seeing > > instances > > + of '(___ptrval___)') - cryptographically insecure, > > + please do not use on production kernels. > > + > > debug_locks_verbose= > > [KNL] verbose self-tests > > Format=<0|1> > > diff --git a/lib/vsprintf.c b/lib/vsprintf.c > > index 3697a19c2b25..6c139b442267 100644 > > --- a/lib/vsprintf.c > > +++ b/lib/vsprintf.c > > @@ -1654,6 +1654,18 @@ char *device_node_string(char *buf, char *end, > > struct device_node *dn, > > return widen_string(buf, buf - buf_start, end, spec); > > } > > > > +/* Make pointers available for printing early in the boot sequence. */ > > +static int debug_early_boot; > > Please make this __ro_after_init too.
Good suggestion. I forgot, we are supposed to be closing security wholes not opening them :) thanks, Tobin.
