From: Timur Tabi <timur@kernel.org>
To: Petr Mladek <pmladek@suse.com>,
Steven Rostedt <rostedt@goodmis.org>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
willy@infradead.org, akpm@linux-foundation.org,
torvalds@linux-foundation.org, roman.fietze@magna.com,
keescook@chromium.org, john.ogness@linutronix.de,
akinobu.mita@gmail.com
Subject: [PATCH] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed
Date: Tue, 2 Feb 2021 14:18:46 -0600 [thread overview]
Message-ID: <20210202201846.716915-1-timur@kernel.org> (raw)
If the make-printk-non-secret command-line parameter is set, then
printk("%p") will print addresses as unhashed. This is useful for
debugging purposes.
A large warning message is displayed if this option is enabled,
because unhashed addresses, while useful for debugging, exposes
kernel addresses which can be a security risk.
Signed-off-by: Timur Tabi <timur@kernel.org>
---
lib/vsprintf.c | 34 ++++++++++++++++++++++++++++++++--
1 file changed, 32 insertions(+), 2 deletions(-)
diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 3b53c73580c5..b9f87084afb0 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2090,6 +2090,30 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
return widen_string(buf, buf - buf_start, end, spec);
}
+/* Disable pointer hashing if requested */
+static bool debug_never_hash_pointers __ro_after_init;
+
+static int __init debug_never_hash_pointers_enable(char *str)
+{
+ debug_never_hash_pointers = true;
+ pr_warn("**********************************************************\n");
+ pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warn("** **\n");
+ pr_warn("** All pointers that are printed to the console will **\n");
+ pr_warn("** be printed as unhashed. **\n");
+ pr_warn("** **\n");
+ pr_warn("** Kernel memory addresses are exposed, which may **\n");
+ pr_warn("** compromise security on your system. **\n");
+ pr_warn("** **\n");
+ pr_warn("** If you see this message and you are not debugging **\n");
+ pr_warn("** the kernel, report this immediately to your vendor! **\n");
+ pr_warn("** **\n");
+ pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
+ pr_warn("**********************************************************\n");
+ return 0;
+}
+early_param("make-printk-non-secret", debug_never_hash_pointers_enable);
+
/*
* Show a '%p' thing. A kernel extension is that the '%p' is followed
* by an extra set of alphanumeric characters that are extended format
@@ -2297,8 +2321,14 @@ char *pointer(const char *fmt, char *buf, char *end, void *ptr,
}
}
- /* default is to _not_ leak addresses, hash before printing */
- return ptr_to_id(buf, end, ptr, spec);
+ /*
+ * default is to _not_ leak addresses, so hash before printing, unless
+ * make-printk-non-secret is specified on the command line.
+ */
+ if (unlikely(debug_never_hash_pointers))
+ return pointer_string(buf, end, ptr, spec);
+ else
+ return ptr_to_id(buf, end, ptr, spec);
}
/*
--
2.25.1
next reply other threads:[~2021-02-02 20:19 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-02 20:18 Timur Tabi [this message]
2021-02-02 21:52 ` [PATCH] lib/vsprintf: make-printk-non-secret printks all addresses as unhashed Kees Cook
2021-02-02 22:19 ` Timur Tabi
2021-02-02 22:34 ` Steven Rostedt
2021-02-02 22:51 ` Linus Torvalds
2021-02-03 18:53 ` Kees Cook
2021-02-04 20:48 ` Pavel Machek
2021-02-04 20:54 ` Steven Rostedt
2021-02-04 21:49 ` Pavel Machek
2021-02-04 21:59 ` Timur Tabi
2021-02-04 22:06 ` Steven Rostedt
2021-02-04 22:11 ` Pavel Machek
2021-02-04 22:17 ` Kees Cook
2021-02-04 22:20 ` Timur Tabi
2021-02-04 22:51 ` Pavel Machek
2021-02-04 22:57 ` Pavel Machek
2021-02-04 22:05 ` Steven Rostedt
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