From: Kees Cook <keescook@chromium.org>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
Peter Rosin <peda@axentia.se>, Andy Shevchenko <andy@kernel.org>,
Matteo Croce <mcroce@microsoft.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH] lib/test_string.c: Add test for strlen()
Date: Wed, 2 Feb 2022 12:52:00 -0800 [thread overview]
Message-ID: <202202021237.487D3DE73@keescook> (raw)
In-Reply-To: <20220202160149.GA2322037@roeck-us.net>
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@linux-m68k.org>
> > Cc: Peter Rosin <peda@axentia.se>
> > Signed-off-by: Kees Cook <keescook@chromium.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.
Which tests?
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),
};
>
> 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
> >
--
Kees Cook
next prev parent reply other threads:[~2022-02-02 20:52 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-01-30 18:36 [PATCH] lib/test_string.c: Add test for strlen() Kees Cook
2022-01-30 18:56 ` Andy Shevchenko
2022-01-30 20:34 ` Kees Cook
2022-01-30 20:13 ` kernel test robot
2022-01-30 20:35 ` Kees Cook
2022-02-02 16:01 ` Guenter Roeck
2022-02-02 16:16 ` Andy Shevchenko
2022-02-02 20:52 ` Kees Cook [this message]
2022-02-02 23:12 ` Guenter Roeck
2022-02-03 8:04 ` Geert Uytterhoeven
2022-02-03 16:41 ` Kees Cook
2022-02-03 17:15 ` Kees Cook
2022-02-03 18:09 ` Geert Uytterhoeven
2022-02-03 19:50 ` Nick Desaulniers
2022-02-03 20:25 ` Kees Cook
2022-02-03 20:45 ` Kees Cook
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