Re: [PATCH 3/3] [v4] lib/vsprintf: no_hash_pointers prints all addresses as unhashed

Marco Elver
2021-03-02T17:01:07Z

On Tue, Mar 02, 2021 at 09:08AM -0500, Steven Rostedt wrote:
> On Tue, 2 Mar 2021 14:49:42 +0100
> Geert Uytterhoeven <geert@linux-m68k.org> wrote:
>
> > > So this is basically a kernel tinyfication issue, right? Is that still pursued
> > > today? Are there better config options suitable for this than CONFIG_DEBUG_KERNEL?
> >
> > As long as I hear about products running Linux on SoCs with 10 MiB of
> > SRAM, I think the answer is yes.
> > I'm not immediately aware of a better config option. There are no more
> > TINY options left, and EXPERT selects DEBUG_KERNEL.
>
> Since the trace_printk() uses the same type of notice, I wonder if we could
> make this into a helper function and just pass in the top part.
>
> + pr_warn("**********************************************************\n");
> + pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
> + pr_warn("** **\n");
>
>
> + pr_warn("** This system shows unhashed kernel memory addresses **\n");
> + pr_warn("** via the console, logs, and other interfaces. This **\n");
> + pr_warn("** might reduce the security of your system. **\n");
>
> Only the above section is really unique. The rest can be a boiler plate.

Short of procedurally generating some of these strings, I was
experimenting with the below.

Would that be reasonable?

Thanks,
-- Marco

------ >8 ------

From: Marco Elver <elver@google.com>
Date: Tue, 2 Mar 2021 15:07:28 +0100
Subject: [PATCH] lib/vsprintf: reduce space taken by no_hash_pointers warning

Move the no_hash_pointers warning string into __initconst section, so
that it is discarded after init. Remove common start/end characters and
remove repeated lines from the array.

Link: https://lkml.kernel.org/r/CAMuHMdULKZCJevVJcp7TxzLdWLjsQPhE8hqxhnztNi9bjT_cEw@mail.gmail.com
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Marco Elver <elver@google.com>
---
lib/vsprintf.c | 30 +++++++++++++++++-------------
1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 41ddc353ebb8..1e63b43955f6 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2094,23 +2094,27 @@ char *fwnode_string(char *buf, char *end, struct fwnode_handle *fwnode,
bool no_hash_pointers __ro_after_init;
EXPORT_SYMBOL_GPL(no_hash_pointers);

+static const char no_hash_pointers_warning[9][55] __initconst = {
+ "******************************************************",
+ " NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE ",
+ " ",
+ " This system shows unhashed kernel memory addresses ",
+ " via the console, logs, and other interfaces. This ",
+ " might reduce the security of your system. ",
+ " If you see this message and you are not debugging ",
+ " the kernel, report this immediately to your system ",
+ " administrator! ",
+};
+
static int __init no_hash_pointers_enable(char *str)
{
+ const int lines[] = { 0, 1, 2, 3, 4, 5, 2, 6, 7, 8, 2, 1, 0 };
+ int i;
+
no_hash_pointers = true;

- pr_warn("**********************************************************\n");
- pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
- pr_warn("** **\n");
- pr_warn("** This system shows unhashed kernel memory addresses **\n");
- pr_warn("** via the console, logs, and other interfaces. This **\n");
- pr_warn("** might reduce the security of 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 system **\n");
- pr_warn("** administrator! **\n");
- pr_warn("** **\n");
- pr_warn("** NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE NOTICE **\n");
- pr_warn("**********************************************************\n");
+ for (i = 0; i < ARRAY_SIZE(lines); i++)
+ pr_warn("**%s**\n", no_hash_pointers_warning[lines[i]]);

return 0;
}
--
2.30.1.766.gb4fecdf3b7-goog