Re: [PATCH] lib/test_string.c: Add test for strlen()
From: Guenter Roeck
Date: Wed Feb 02 2022 - 18:12:09 EST
On 2/2/22 12:52, Kees Cook wrote:
On Wed, Feb 02, 2022 at 08:01:49AM -0800, Guenter Roeck wrote:
On Sun, Jan 30, 2022 at 10:36:53AM -0800, Kees Cook wrote:
Add a simple test for strlen() functionality, including using it as a
constant expression.
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Peter Rosin <peda@xxxxxxxxxx>
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
I'll be taking this as part of my Clang FORTIFY_SOURCE series.
---
lib/test_string.c | 37 +++++++++++++++++++++++++++++++++++++
1 file changed, 37 insertions(+)
diff --git a/lib/test_string.c b/lib/test_string.c
index 9dfd6f52de92..59994f552c48 100644
--- a/lib/test_string.c
+++ b/lib/test_string.c
@@ -179,6 +179,38 @@ static __init int strnchr_selftest(void)
return 0;
}
+/*
+ * Unlike many other string functions, strlen() can be used in
+ * static initializers when string lengths are known at compile
+ * time. (i.e. Under these conditions, strlen() is a constant
+ * expression.) Make sure it can be used this way.
+ */
+static const int strlen_ce = strlen("tada, a constant expression");
+
This results in:
lib/test_string.c:188:30: error: initializer element is not constant
188 | static const int strlen_ce = strlen("tada, a constant expression");
for several of my tests. I don't think you can mandate that a compiler
implements this.
Which tests?
Some examples:
Build reference: next-20220202
Compiler version: m68k-linux-gcc (GCC) 11.2.0
Building m68k:defconfig ... failed
--------------
Error log:
lib/test_string.c:188:30: error: initializer element is not constant
188 | static const int strlen_ce = strlen("tada, a constant expression");
Building mips:malta_defconfig:nocd:smp:net,e1000:initrd ... failed
------------
Error log:
lib/test_string.c:188:30: error: initializer element is not constant
static const int strlen_ce = strlen("tada, a constant expression");
Building i386:q35:Broadwell:defconfig:smp:ata:net,rtl8139:hd ... failed
------------
Error log:
lib/test_string.c:188:30: error: initializer element is not constant
188 | static const int strlen_ce = strlen("tada, a constant expression");
i386 and is defconfig + CONFIG_STRING_SELFTEST=y; mips is
malta_defconfig + CONFIG_STRING_SELFTEST=y. All use gcc 11.2.
There may be more, but there are so many failures in -next right now
that I may be missing some.
This property of strlen() is already required by our builds (this is how
I tripped over it). For example:
drivers/firmware/xilinx/zynqmp-debug.c:
#define PM_API(id) {id, #id, strlen(#id)}
static struct pm_api_info pm_api_list[] = {
PM_API(PM_GET_API_VERSION),
PM_API(PM_QUERY_DATA),
};
I do not think that it is a C standard that strlen() on a constant string
must be compile-time evaluated and result in a constant.
Anyway, key difference, I think, is the presence of an architecture-specific
version of strlen(), or the maybe non-presence of __HAVE_ARCH_STRLEN,
or the definition of strlen() in include/linux/fortify-string.h.
Guenter