On 06/20/2018 08:15 PM, Tobin C. Harding wrote: > On Wed, Jun 20, 2018 at 04:38:05PM -0700, Randy Dunlap wrote: >> On 06/20/2018 04:22 PM, Tobin C. Harding wrote: >>> 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. >> >> Sorry, I'm still confused by this paragraph. It seems to say two different >> things. > > My bad, I got totally confused myself. After all this time you would > think I knew which specifier hashed and which didn't. My apologies, > how about this: > > [KNL] Enable printing [hashed] pointers early in > the boot sequence. If enabled, we use a weak hash > instead of siphash to hash pointers. Use this option if > you are seeing instances of '(___ptrval___)') and need > to see a value (hashed pointer) instead. > Cryptographically > insecure, please do not use on production kernels. > > > thanks for your patience, > Tobin.
Yes, that's good. Thanks. -- ~Randy
