On Wed, Jun 20, 2018 at 03:36:44PM -0700, Randy Dunlap wrote: > On 06/20/2018 03:30 PM, Tobin C. Harding wrote: > > On Wed, Jun 20, 2018 at 09:09:49AM -0700, Randy Dunlap wrote: > >> On 06/19/2018 09:20 PM, Tobin C. Harding wrote: > >>> Currently printing [hashed] pointers requires enough entropy to be > >>> available. Early in the boot sequence this may not be the case > >>> 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_boot_weak_hash is enabled use > >>> cryptographically insecure hashing and hash pointer value immediately. > >>> > >>> Signed-off-by: Tobin C. Harding <m...@tobin.cc> > >>> Reviewed-by: Steven Rostedt (VMware) <rost...@goodmis.org> > >>> --- > >>> Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ > >>> lib/vsprintf.c | 17 +++++++++++++++++ > >>> 2 files changed, 26 insertions(+) > >>> > >>> diff --git a/Documentation/admin-guide/kernel-parameters.txt > >>> b/Documentation/admin-guide/kernel-parameters.txt > >>> index 638342d0a095..a116fc0366b0 100644 > >>> --- a/Documentation/admin-guide/kernel-parameters.txt > >>> +++ b/Documentation/admin-guide/kernel-parameters.txt > >>> @@ -748,6 +748,15 @@ > >>> > >>> debug [KNL] Enable kernel debugging (events log level). > >>> > >>> + debug_boot_weak_hash > >>> + [KNL] Enable printing pointers 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 > >> > >> maybe: > >> to see hashed pointer values > >> i.e., not raw pointers. > > > > You cannot see 'raw pointers' anyways? > > only if using %px ? > > Maybe it's just terminology. I don't consider a hashed value as a pointer > value. > It's just a key or handle or some other number, but it's not a pointer. > > >> > >>> + seeing instances of '(___ptrval___)'). > >>> + Cryptographically insecure, please do not use on > >>> + production kernels. > > > > thanks for the review, I don't quiet see how to use your suggestion to > > make the text clearer. If you still feel this change is needed perhaps > > you could write so I understand i.e 'Use this option if ...' > > > OK, if you are good with it, I am too. :)
I get you know. I agree, how about this [KNL] Enable printing pointers 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 print pointers with %px during early boot (i.e you are seeing instances of '(___ptrval___)'). Cryptographically insecure, please do not use on production kernels. thanks for clarifying, Tobin.