Messages in this thread Patch in this message | | | From | "Tobin C. Harding" <> | Subject | [PATCH v7 4/4] vsprintf: Add command line option debug_boot_weak_hash | Date | Tue, 12 Jun 2018 10:39:14 +1000 |
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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.
Cc: Anna-Maria Gleixner <anna-maria@linutronix.de> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Tobin C. Harding <me@tobin.cc> --- Documentation/admin-guide/kernel-parameters.txt | 9 +++++++++ lib/vsprintf.c | 18 ++++++++++++++++++ 2 files changed, 27 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 + 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 c445f9f28760..6d2479eb7c2b 100644 --- a/lib/vsprintf.c +++ b/lib/vsprintf.c @@ -1651,6 +1651,18 @@ 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_boot_weak_hash __ro_after_init; +EXPORT_SYMBOL(debug_boot_weak_hash); + +static int __init debug_boot_weak_hash_enable(char *str) +{ + debug_boot_weak_hash = 1; + pr_info("debug_boot_weak_hash enabled\n"); + return 0; +} +early_param("debug_boot_weak_hash", debug_boot_weak_hash_enable); + static DEFINE_STATIC_KEY_TRUE(not_filled_random_ptr_key); static siphash_key_t ptr_key __read_mostly; @@ -1703,6 +1715,12 @@ 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_boot_weak_hash)) { + hashval = hash_long((unsigned long)ptr, 32); + return pointer_string(buf, end, (const void *)hashval, spec); + } + if (static_branch_unlikely(¬_filled_random_ptr_key)) { spec.field_width = 2 * sizeof(ptr); /* string length must be less than default_width */ -- 2.7.4
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