[PATCH 2/2] lib/vsprintf: reduce space taken by no_hash_pointers warning

Marco Elver
2021-03-05T19:42:55Z

Move the no_hash_pointers warning string into __initconst section, so
that it is discarded after init. Remove common start/end characters.
Also remove repeated lines from the array, since the compiler can't
remove duplicate strings for us since the array must appear in
__initconst as defined.

Note, a similar message appears in kernel/trace/trace.c, but compiling
the feature is guarded by CONFIG_TRACING. It is not immediately obvious
if a space-concious kernel would prefer CONFIG_TRACING=n. Therefore, it
makes sense to keep the message for no_hash_pointers as __initconst, and
not move the NOTICE-printing to a common function.

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 4a14889ccb35..1095689c9c97 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -2094,26 +2094,30 @@ 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[8][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)
{
+ /* Indices into no_hash_pointers_warning; -1 is an empty line. */
+ const int lines[] = { 0, 1, -1, 2, 3, 4, -1, 5, 6, 7, -1, 1, 0 };
+ int i;
+
if (no_hash_pointers)
return 0;

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("**%54s**\n", i == -1 ? "" : no_hash_pointers_warning[lines[i]]);

return 0;
}
--
2.30.1.766.gb4fecdf3b7-goog