From 5ead723a20e0447bc7db33dc3070b420e5f80aa6 Mon Sep 17 00:00:00 2001 From: Timur Tabi Date: Sun, 14 Feb 2021 10:13:48 -0600 Subject: lib/vsprintf: no_hash_pointers prints all addresses as unhashed If the no_hash_pointers command line parameter is set, then printk("%p") will print pointers as unhashed, which is useful for debugging purposes. This change applies to any function that uses vsprintf, such as print_hex_dump() and seq_buf_printf(). A large warning message is displayed if this option is enabled. Unhashed pointers expose kernel addresses, which can be a security risk. Also update test_printf to skip the hashed pointer tests if the command-line option is set. Signed-off-by: Timur Tabi Acked-by: Petr Mladek Acked-by: Randy Dunlap Acked-by: Sergey Senozhatsky Acked-by: Vlastimil Babka Acked-by: Marco Elver Signed-off-by: Petr Mladek Link: https://lore.kernel.org/r/20210214161348.369023-4-timur@kernel.org --- Documentation/admin-guide/kernel-parameters.txt | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'Documentation/admin-guide') diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c722ec19cd00..c549bc789108 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3281,6 +3281,21 @@ in certain environments such as networked servers or real-time systems. + no_hash_pointers + Force pointers printed to the console or buffers to be + unhashed. By default, when a pointer is printed via %p + format string, that pointer is "hashed", i.e. obscured + by hashing the pointer value. This is a security feature + that hides actual kernel addresses from unprivileged + users, but it also makes debugging the kernel more + difficult since unequal pointers can no longer be + compared. However, if this command-line option is + specified, then all normal pointers will have their true + value printed. Pointers printed via %pK may still be + hashed. This option should only be specified when + debugging the kernel. Please do not use on production + kernels. + nohibernate [HIBERNATION] Disable hibernation and resume. nohz= [KNL] Boottime enable/disable dynamic ticks -- cgit v1.2.3