[PATCH v7 08/10] livepatch/selftests: add __asm__ symbol renaming examples

Joe Lawrence
2023-03-06T14:13:39Z

GCC can rename symbols like static data and optimized functions, adding
a suffix that includes illegal C characters. Extend the klp-convert
examples to demonstrate how to use __asm__ renaming from C code to
create klp-relocations to such renamed symbols.

Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
---
lib/livepatch/test_klp_convert.h | 2 ++
lib/livepatch/test_klp_convert1.c | 8 ++++++++
lib/livepatch/test_klp_convert_mod_a.c | 6 ++++++
lib/livepatch/test_klp_convert_mod_b.c | 6 ++++++
tools/testing/selftests/livepatch/test-livepatch.sh | 4 ++++
5 files changed, 26 insertions(+)

diff --git a/lib/livepatch/test_klp_convert.h b/lib/livepatch/test_klp_convert.h
index 5d97bc546d6e..42befbfd63cb 100644
--- a/lib/livepatch/test_klp_convert.h
+++ b/lib/livepatch/test_klp_convert.h
@@ -10,5 +10,7 @@ extern char driver_name[];
extern char homonym_string[];
extern const char *get_homonym_string(void);
extern const char *test_klp_get_driver_name(void);
+extern char klp_string_a[] __asm__("klp_string.12345");
+extern char klp_string_b[] __asm__("klp_string.67890");

#endif
diff --git a/lib/livepatch/test_klp_convert1.c b/lib/livepatch/test_klp_convert1.c
index d4e1163c01cc..9541f40d70a8 100644
--- a/lib/livepatch/test_klp_convert1.c
+++ b/lib/livepatch/test_klp_convert1.c
@@ -25,6 +25,12 @@ static noinline void print_homonym_string(void)
pr_info("get_homonym_string(), 1: %s\n", get_homonym_string());
}

+static noinline void print_static_strings(void)
+{
+ pr_info("klp_string.12345 = %s\n", klp_string_a);
+ pr_info("klp_string.67890 = %s\n", klp_string_b);
+}
+
/* provide a sysfs handle to invoke debug functions */
static int print_debug;
static int print_debug_set(const char *val, const struct kernel_param *kp)
@@ -32,6 +38,7 @@ static int print_debug_set(const char *val, const struct kernel_param *kp)
print_saved_command_line();
print_driver_name();
print_homonym_string();
+ print_static_strings();

return 0;
}
@@ -67,6 +74,7 @@ KLP_MODULE_RELOC(test_klp_convert_mod) test_klp_convert_mod_relocs_a[] = {
KLP_SYMPOS(homonym_string, 1),
KLP_SYMPOS(get_homonym_string, 1),
KLP_SYMPOS(test_klp_get_driver_name, 0),
+ KLP_SYMPOS(klp_string_b, 1),
};

static struct klp_func funcs[] = {
diff --git a/lib/livepatch/test_klp_convert_mod_a.c b/lib/livepatch/test_klp_convert_mod_a.c
index ae5e911fbb9b..9af0fcab0c8d 100644
--- a/lib/livepatch/test_klp_convert_mod_a.c
+++ b/lib/livepatch/test_klp_convert_mod_a.c
@@ -20,6 +20,12 @@ __used static const char *get_homonym_string(void)
return homonym_string;
}

+__used static void static_string_function(void)
+{
+ __used static char klp_string[] __asm__("klp_string.12345") =
+ __FILE__ " static string";
+}
+
MODULE_LICENSE("GPL");
MODULE_AUTHOR("Joe Lawrence <joe.lawrence@redhat.com>");
MODULE_DESCRIPTION("Livepatch test: klp-convert module");
diff --git a/lib/livepatch/test_klp_convert_mod_b.c b/lib/livepatch/test_klp_convert_mod_b.c
index 5eca8a4cae38..0a68e898fe03 100644
--- a/lib/livepatch/test_klp_convert_mod_b.c
+++ b/lib/livepatch/test_klp_convert_mod_b.c
@@ -11,3 +11,9 @@ __used static const char *get_homonym_string(void)
{
return homonym_string;
}
+
+__used static void static_string_function(void)
+{
+ __used static char klp_string[] __asm__("klp_string.67890") =
+ __FILE__ " static string";
+}
diff --git a/tools/testing/selftests/livepatch/test-livepatch.sh b/tools/testing/selftests/livepatch/test-livepatch.sh
index bcb8b468b80a..ec3b6c919b01 100755
--- a/tools/testing/selftests/livepatch/test-livepatch.sh
+++ b/tools/testing/selftests/livepatch/test-livepatch.sh
@@ -200,6 +200,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD
$MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD
$MOD_KLP_CONVERT1: homonym_string, 1: homonym string A
$MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A
+test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string
+test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string
% echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled
livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition
livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition
@@ -265,6 +267,8 @@ $MOD_KLP_CONVERT1: driver_name, 0: $MOD_KLP_CONVERT_MOD
$MOD_KLP_CONVERT1: test_klp_get_driver_name(), 0: $MOD_KLP_CONVERT_MOD
$MOD_KLP_CONVERT1: homonym_string, 1: homonym string A
$MOD_KLP_CONVERT1: get_homonym_string(), 1: homonym string A
+test_klp_convert1: klp_string.12345 = lib/livepatch/test_klp_convert_mod_a.c static string
+test_klp_convert1: klp_string.67890 = lib/livepatch/test_klp_convert_mod_b.c static string
% echo 0 > /sys/kernel/livepatch/$MOD_KLP_CONVERT1/enabled
livepatch: '$MOD_KLP_CONVERT1': initializing unpatching transition
livepatch: '$MOD_KLP_CONVERT1': starting unpatching transition
--
2.39.2