linux-kernel - [PATCH 1/2] livepatch: fix non-static warnings

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Date:   Fri, 14 Dec 2018 17:56:09 +0100
From:   Nicholas Mc Guire <hofrat@...dl.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     Jessica Yu <jeyu@...nel.org>, Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>, live-patching@...r.kernel.org,
        linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH 1/2] livepatch: fix non-static warnings

Sparse reported warnings about non-static symbols. For the variables a
simple static attribute is fine - for those symbols referenced by
livepatch via klp_func the symbol-names must be unmodified in the
relocation table - to resolve this the __noclone attribute (as 
suggested by Joe Lawrence <joe.lawrence@...hat.com>) is used
for the statically declared functions.

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
Link: https://lkml.org/lkml/2018/12/13/827
---

sparse reported the following warnings:

  CHECK   samples/livepatch/livepatch-shadow-fix1.c
samples/livepatch/livepatch-shadow-fix1.c:74:14: warning: symbol
 'livepatch_fix1_dummy alloc' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-fix1.c:116:6: warning: symbol
 'livepatch_fix1_dummy free' was not declared. Should it be static?

  CHECK   samples/livepatch/livepatch-shadow-mod.c
samples/livepatch/livepatch-shadow-mod.c:99:1: warning: symbol
 'dummy_list' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:100:1: warning: symbol
 'dummy_list_mutex' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:107:23: warning: symbol
 'dummy_alloc' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:132:15: warning: symbol
 'dummy_free' was not declared. Should it be static?
samples/livepatch/livepatch-shadow-mod.c:140:15: warning: symbol
 'dummy_check' was not declared. Should it be static?

Patch was compile tested with: x86_64_defconfig + FTRACE=y
FUNCTION_TRACER=y, EXPERT=y, LATENCYTOP=y, SAMPLES=y,
SAMPLE_LIVEPATCH=y

Patch was runtested on an Intel i3 with:
   insmod samples/livepatch/livepatch-shadow-mod.ko
   insmod samples/livepatch/livepatch-shadow-fix1.ko
   insmod samples/livepatch/livepatch-shadow-fix2.ko
   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix2/enabled
   echo 0 > /sys/kernel/livepatch/livepatch_shadow_fix1/enabled
   rmmod livepatch-shadow-fix2
   rmmod livepatch-shadow-fix1
   rmmod livepatch-shadow-mod
and dmesg output checked.

Patch is against 4.20-rc6 (localversion-next is next-20181214)

 samples/livepatch/livepatch-shadow-fix1.c |  4 ++--
 samples/livepatch/livepatch-shadow-mod.c  | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/samples/livepatch/livepatch-shadow-fix1.c b/samples/livepatch/livepatch-shadow-fix1.c
index 49b1355..eaab10f 100644
--- a/samples/livepatch/livepatch-shadow-fix1.c
+++ b/samples/livepatch/livepatch-shadow-fix1.c
@@ -71,7 +71,7 @@ static int shadow_leak_ctor(void *obj, void *shadow_data, void *ctor_data)
 	return 0;
 }
 
-struct dummy *livepatch_fix1_dummy_alloc(void)
+static __noclone struct dummy *livepatch_fix1_dummy_alloc(void)
 {
 	struct dummy *d;
 	void *leak;
@@ -108,7 +108,7 @@ static void livepatch_fix1_dummy_leak_dtor(void *obj, void *shadow_data)
 			 __func__, d, *shadow_leak);
 }
 
-void livepatch_fix1_dummy_free(struct dummy *d)
+static __noclone void livepatch_fix1_dummy_free(struct dummy *d)
 {
 	void **shadow_leak;
 
diff --git a/samples/livepatch/livepatch-shadow-mod.c b/samples/livepatch/livepatch-shadow-mod.c
index 4c54b25..0a72bc2 100644
--- a/samples/livepatch/livepatch-shadow-mod.c
+++ b/samples/livepatch/livepatch-shadow-mod.c
@@ -30,6 +30,11 @@
  * memory leak, please load these modules at your own risk -- some
  * amount of memory may leaked before the bug is patched.
  *
+ * NOTE - the __noclone attribute to those functions that are to be
+ * shared with other modules while being declared static. As livepatch
+ * needs the unmodified symbol names and the usual "static" would
+ * invoke gccs cloning mechanism that renames the functions this
+ * needs to be suppressed with the additional __noclone attribute.
  *
  * Usage
  * -----
@@ -96,15 +101,15 @@ MODULE_DESCRIPTION("Buggy module for shadow variable demo");
  * Keep a list of all the dummies so we can clean up any residual ones
  * on module exit
  */
-LIST_HEAD(dummy_list);
-DEFINE_MUTEX(dummy_list_mutex);
+static LIST_HEAD(dummy_list);
+static DEFINE_MUTEX(dummy_list_mutex);
 
 struct dummy {
 	struct list_head list;
 	unsigned long jiffies_expire;
 };
 
-noinline struct dummy *dummy_alloc(void)
+static __noclone noinline struct dummy *dummy_alloc(void)
 {
 	struct dummy *d;
 	void *leak;
@@ -125,7 +130,7 @@ noinline struct dummy *dummy_alloc(void)
 	return d;
 }
 
-noinline void dummy_free(struct dummy *d)
+static __noclone noinline void dummy_free(struct dummy *d)
 {
 	pr_info("%s: dummy @ %p, expired = %lx\n",
 		__func__, d, d->jiffies_expire);
@@ -133,7 +138,8 @@ noinline void dummy_free(struct dummy *d)
 	kfree(d);
 }
 
-noinline bool dummy_check(struct dummy *d, unsigned long jiffies)
+static __noclone noinline bool dummy_check(struct dummy *d,
+					   unsigned long jiffies)
 {
 	return time_after(jiffies, d->jiffies_expire);
 }
-- 
2.1.4