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UPSTREAM: lib/vsprintf: no_hash_pointers prints all addresses as unhashed

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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 <timur@kernel.org>
Acked-by: Petr Mladek <pmladek@suse.com>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20210214161348.369023-4-timur@kernel.org

(cherry picked from commit 5ead723a20e0447bc7db33dc3070b420e5f80aa6)
Bug: 181049978
Change-Id: I06c5cfdc0b4c12f38c9109179f27bf2b54ac57e8
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>
This commit is contained in:
Timur Tabi
2021-02-14 10:13:48 -06:00
committed by Suren Baghdasaryan
parent 0e1b1c2d68
commit fc461a19b0
3 changed files with 57 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
Documentation/admin-guide/kernel-parameters.txt
View File

@@ -3327,6 +3327,21 @@
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