Messages in this thread Patch in this message | | | From | "Tobin C. Harding" <> | Subject | [PATCH v2 4/4] vsprintf: Add command line option debug_early_boot | Date | Thu, 3 May 2018 08:50:26 +1000 |
| |
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; +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
| |