[PATCH] kunit/fortify: Replace "volatile" with OPTIMIZER_HIDE_VAR()

Kees Cook
2025-03-12T00:04:45Z

It does seem that using "volatile" isn't going to be sane compared to
using OPTIMIZER_HIDE_VAR() going forward. Some strange interactions[1]
with the sanitizers have been observed in the self-test code, so replace
the logic.

Reported-by: Nathan Chancellor <nathan@kernel.org>
Closes: https://github.com/ClangBuiltLinux/linux/issues/2075 [1]
Signed-off-by: Kees Cook <kees@kernel.org>
---
Cc: Nathan Chancellor <nathan@kernel.org>
Cc: linux-hardening@vger.kernel.org
---
lib/tests/fortify_kunit.c | 139 +++++++++++++++++++++-----------------
1 file changed, 77 insertions(+), 62 deletions(-)

diff --git a/lib/tests/fortify_kunit.c b/lib/tests/fortify_kunit.c
index 18dcdedf777f..29ffc62a71e3 100644
--- a/lib/tests/fortify_kunit.c
+++ b/lib/tests/fortify_kunit.c
@@ -411,8 +411,6 @@ struct fortify_padding {
char buf[32];
unsigned long bytes_after;
};
-/* Force compiler into not being able to resolve size at compile-time. */
-static volatile int unconst;

static void fortify_test_strlen(struct kunit *test)
{
@@ -537,57 +535,56 @@ static void fortify_test_strncpy(struct kunit *test)
{
struct fortify_padding pad = { };
char src[] = "Copy me fully into a small buffer and I will overflow!";
+ size_t sizeof_buf = sizeof(pad.buf);
+
+ OPTIMIZER_HIDE_VAR(sizeof_buf);

/* Destination is %NUL-filled to start with. */
KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 3], '\0');
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);

/* Legitimate strncpy() 1 less than of max size. */
- KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
- sizeof(pad.buf) + unconst - 1)
+ KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src, sizeof_buf - 1)
== pad.buf);
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
/* Only last byte should be %NUL */
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 3], '\0');

/* Legitimate (though unterminated) max-size strncpy. */
- KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
- sizeof(pad.buf) + unconst)
+ KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src, sizeof_buf)
== pad.buf);
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
/* No trailing %NUL -- thanks strncpy API. */
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
/* But we will not have gone beyond. */
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);

/* Now verify that FORTIFY is working... */
- KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
- sizeof(pad.buf) + unconst + 1)
+ KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src, sizeof_buf + 1)
== pad.buf);
/* Should catch the overflow. */
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
/* And we will not have gone beyond. */
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);

/* And further... */
- KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src,
- sizeof(pad.buf) + unconst + 2)
+ KUNIT_ASSERT_TRUE(test, strncpy(pad.buf, src, sizeof_buf + 2)
== pad.buf);
/* Should catch the overflow. */
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
/* And we will not have gone beyond. */
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
}
@@ -596,55 +593,56 @@ static void fortify_test_strscpy(struct kunit *test)
{
struct fortify_padding pad = { };
char src[] = "Copy me fully into a small buffer and I will overflow!";
+ size_t sizeof_buf = sizeof(pad.buf);
+ size_t sizeof_src = sizeof(src);
+
+ OPTIMIZER_HIDE_VAR(sizeof_buf);
+ OPTIMIZER_HIDE_VAR(sizeof_src);

/* Destination is %NUL-filled to start with. */
KUNIT_EXPECT_EQ(test, pad.bytes_before, 0);
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 3], '\0');
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);

/* Legitimate strscpy() 1 less than of max size. */
- KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
- sizeof(pad.buf) + unconst - 1),
+ KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src, sizeof_buf - 1),
-E2BIG);
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
/* Keeping space for %NUL, last two bytes should be %NUL */
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 3], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 3], '\0');

/* Legitimate max-size strscpy. */
- KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
- sizeof(pad.buf) + unconst),
+ KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src, sizeof_buf),
-E2BIG);
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0);
/* A trailing %NUL will exist. */
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');

/* Now verify that FORTIFY is working... */
- KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
- sizeof(pad.buf) + unconst + 1),
+ KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src, sizeof_buf + 1),
-E2BIG);
/* Should catch the overflow. */
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1);
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
/* And we will not have gone beyond. */
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);

/* And much further... */
- KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src,
- sizeof(src) * 2 + unconst),
+ KUNIT_ASSERT_EQ(test, strscpy(pad.buf, src, sizeof_src * 2),
-E2BIG);
/* Should catch the overflow. */
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 2);
- KUNIT_EXPECT_EQ(test, pad.buf[sizeof(pad.buf) - 1], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
- KUNIT_EXPECT_NE(test, pad.buf[sizeof(pad.buf) - 2], '\0');
+ KUNIT_EXPECT_EQ(test, pad.buf[sizeof_buf - 1], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
+ KUNIT_EXPECT_NE(test, pad.buf[sizeof_buf - 2], '\0');
/* And we will not have gone beyond. */
KUNIT_EXPECT_EQ(test, pad.bytes_after, 0);
}
@@ -784,7 +782,9 @@ static void fortify_test_strlcat(struct kunit *test)
struct fortify_padding pad = { };
char src[sizeof(pad.buf)] = { };
int i, partial;
- int len = sizeof(pad.buf) + unconst;
+ int len = sizeof(pad.buf);
+
+ OPTIMIZER_HIDE_VAR(len);

/* Fill 15 bytes with valid characters. */
partial = sizeof(src) / 2 - 1;
@@ -874,28 +874,32 @@ struct fortify_zero_sized {
#define __fortify_test(memfunc) \
static void fortify_test_##memfunc(struct kunit *test) \
{ \
- struct fortify_zero_sized zero = { }; \
+ struct fortify_zero_sized empty = { }; \
struct fortify_padding pad = { }; \
char srcA[sizeof(pad.buf) + 2]; \
char srcB[sizeof(pad.buf) + 2]; \
- size_t len = sizeof(pad.buf) + unconst; \
+ size_t len = sizeof(pad.buf); \
+ size_t zero = 0; \
+ \
+ OPTIMIZER_HIDE_VAR(len); \
+ OPTIMIZER_HIDE_VAR(zero); \
\
memset(srcA, 'A', sizeof(srcA)); \
KUNIT_ASSERT_EQ(test, srcA[0], 'A'); \
memset(srcB, 'B', sizeof(srcB)); \
KUNIT_ASSERT_EQ(test, srcB[0], 'B'); \
\
- memfunc(pad.buf, srcA, 0 + unconst); \
+ memfunc(pad.buf, srcA, zero); \
KUNIT_EXPECT_EQ(test, pad.buf[0], '\0'); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0); \
- memfunc(pad.buf + 1, srcB, 1 + unconst); \
+ memfunc(pad.buf + 1, srcB, zero + 1); \
KUNIT_EXPECT_EQ(test, pad.buf[0], '\0'); \
KUNIT_EXPECT_EQ(test, pad.buf[1], 'B'); \
KUNIT_EXPECT_EQ(test, pad.buf[2], '\0'); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0); \
- memfunc(pad.buf, srcA, 1 + unconst); \
+ memfunc(pad.buf, srcA, zero + 1); \
KUNIT_EXPECT_EQ(test, pad.buf[0], 'A'); \
KUNIT_EXPECT_EQ(test, pad.buf[1], 'B'); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
@@ -921,10 +925,10 @@ static void fortify_test_##memfunc(struct kunit *test) \
/* Reset error counter. */ \
fortify_write_overflows = 0; \
/* Copy nothing into nothing: no errors. */ \
- memfunc(zero.buf, srcB, 0 + unconst); \
+ memfunc(empty.buf, srcB, zero); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 0); \
- memfunc(zero.buf, srcB, 1 + unconst); \
+ memfunc(empty.buf, srcB, zero + 1); \
KUNIT_EXPECT_EQ(test, fortify_read_overflows, 0); \
KUNIT_EXPECT_EQ(test, fortify_write_overflows, 1); \
}
@@ -936,7 +940,9 @@ static void fortify_test_memscan(struct kunit *test)
char haystack[] = "Where oh where is my memory range?";
char *mem = haystack + strlen("Where oh where is ");
char needle = 'm';
- size_t len = sizeof(haystack) + unconst;
+ size_t len = sizeof(haystack);
+
+ OPTIMIZER_HIDE_VAR(len);

KUNIT_ASSERT_PTR_EQ(test, memscan(haystack, needle, len),
mem);
@@ -955,7 +961,9 @@ static void fortify_test_memchr(struct kunit *test)
char haystack[] = "Where oh where is my memory range?";
char *mem = haystack + strlen("Where oh where is ");
char needle = 'm';
- size_t len = sizeof(haystack) + unconst;
+ size_t len = sizeof(haystack);
+
+ OPTIMIZER_HIDE_VAR(len);

KUNIT_ASSERT_PTR_EQ(test, memchr(haystack, needle, len),
mem);
@@ -974,7 +982,9 @@ static void fortify_test_memchr_inv(struct kunit *test)
char haystack[] = "Where oh where is my memory range?";
char *mem = haystack + 1;
char needle = 'W';
- size_t len = sizeof(haystack) + unconst;
+ size_t len = sizeof(haystack);
+
+ OPTIMIZER_HIDE_VAR(len);

/* Normal search is okay. */
KUNIT_ASSERT_PTR_EQ(test, memchr_inv(haystack, needle, len),
@@ -993,8 +1003,11 @@ static void fortify_test_memcmp(struct kunit *test)
{
char one[] = "My mind is going ...";
char two[] = "My mind is going ... I can feel it.";
- size_t one_len = sizeof(one) + unconst - 1;
- size_t two_len = sizeof(two) + unconst - 1;
+ size_t one_len = sizeof(one) - 1;
+ size_t two_len = sizeof(two) - 1;
+
+ OPTIMIZER_HIDE_VAR(one_len);
+ OPTIMIZER_HIDE_VAR(two_len);

/* We match the first string (ignoring the %NUL). */
KUNIT_ASSERT_EQ(test, memcmp(one, two, one_len), 0);
@@ -1015,7 +1028,9 @@ static void fortify_test_kmemdup(struct kunit *test)
{
char src[] = "I got Doom running on it!";
char *copy;
- size_t len = sizeof(src) + unconst;
+ size_t len = sizeof(src);
+
+ OPTIMIZER_HIDE_VAR(len);

/* Copy is within bounds. */
copy = kmemdup(src, len, GFP_KERNEL);
--
2.34.1