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Date: Wed, 2 Feb 2022 08:01:49 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Kees Cook <keescook@...omium.org>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>,
Peter Rosin <peda@...ntia.se>,
Andy Shevchenko <andy@...nel.org>,
Matteo Croce <mcroce@...rosoft.com>,
Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH] lib/test_string.c: Add test for strlen()
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@...ux-m68k.org>
> Cc: Peter Rosin <peda@...ntia.se>
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> 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.
Guenter
> +static __init int strlen_selftest(void)
> +{
> + /* String length ruler: 123456789012345 */
> + static const char normal[] = "I am normal";
> + static const char *ptr = "where do I go?";
> + static const char trailing[] = "hidden NULLs\0\0\0";
> + static const char leading[] = "\0\0hidden text";
> +
> + if (strlen(normal) != 11)
> + return 0x100001;
> + if (strlen(ptr++) != 14)
> + return 0x100002;
> + if (strlen(ptr++) != 13)
> + return 0x100003;
> + if (strlen(trailing) != 12)
> + return 0x100004;
> + if (strlen(leading) != 0)
> + return 0x100005;
> + if (strlen_ce != 27)
> + return 0x100006;
> +
> + return 0;
> +}
> +
> static __exit void string_selftest_remove(void)
> {
> }
> @@ -212,6 +244,11 @@ static __init int string_selftest_init(void)
> if (subtest)
> goto fail;
>
> + test = 5;
> + subtest = strlen_selftest();
> + if (subtest)
> + goto fail;
> +
> pr_info("String selftests succeeded\n");
> return 0;
> fail:
> --
> 2.30.2
>
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