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authorTobin C. Harding <me@tobin.cc>2018-06-22 09:15:34 +1000
committerTheodore Ts'o <tytso@mit.edu>2018-07-17 21:32:48 -0400
commit3672476edaa0660eb833f54fa9edeb505417b75c (patch)
treed60f9e1875ca9fe64a831be8ec83bebcc416257a /lib/vsprintf.c
parent1c4facb846c7f863bc65483394e80acdbacf671b (diff)
downloadlinux-3672476edaa0660eb833f54fa9edeb505417b75c.tar.bz2
vsprintf: Add command line option debug_boot_weak_hash
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. Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Tobin C. Harding <me@tobin.cc> Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Diffstat (limited to 'lib/vsprintf.c')
-rw-r--r--lib/vsprintf.c17
1 files changed, 17 insertions, 0 deletions
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 6c1fb395bddf..1ee2829f3b54 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -1651,6 +1651,17 @@ 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;
+
+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 +1714,12 @@ 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(&not_filled_random_ptr_key)) {
spec.field_width = 2 * sizeof(ptr);
/* string length must be less than default_width */