Messages in this thread | | | From | Kees Cook <> | Date | Wed, 2 May 2018 21:57:57 -0700 | Subject | Re: [PATCH v2 4/4] vsprintf: Add command line option debug_early_boot |
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On Wed, May 2, 2018 at 3:50 PM, Tobin C. Harding <me@tobin.cc> 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 <me@tobin.cc> > --- > 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.
-Kees
> +EXPORT_SYMBOL(debug_early_boot); > + > +static int __init debug_early_boot_enable(char *str) > +{ > + debug_early_boot = 1; > + pr_info("debug_early_boot enabled\n"); > + return 0; > +} > +early_param("debug_early_boot", debug_early_boot_enable); > + > static bool have_filled_random_ptr_key __read_mostly; > static siphash_key_t ptr_key __read_mostly; > > @@ -1707,6 +1719,12 @@ static char *ptr_to_id(char *buf, char *end, void *ptr, struct printf_spec spec) > const char *str = sizeof(ptr) == 8 ? "(____ptrval____)" : "(ptrval)"; > unsigned long hashval; > > + /* When debugging early boot use non-cryptographically secure hash */ > + if (unlikely(debug_early_boot)) { > + hashval = hash_long((unsigned long)ptr, 32); > + return pointer_string(buf, end, (const void *)hashval, spec); > + } > + > if (unlikely(!have_filled_random_ptr_key)) { > spec.field_width = 2 * sizeof(ptr); > /* string length must be less than default_width */ > -- > 2.7.4 >
-- Kees Cook Pixel Security
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