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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 25 Aug 2021 14:48:30 -0700
Message-ID: <CAKwvOdmY2DQbjKutcofN3zsiz_majg6UnhMjMWbamVRhaRPhsw@mail.gmail.com>
Subject: Re: [PATCH for-next 14/25] lib/string: Move helper functions out of string.c
To:     Kees Cook <keescook@chromium.org>
Cc:     linux-kernel@vger.kernel.org,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Daniel Micay <danielmicay@gmail.com>,
        Francis Laniel <laniel_francis@privacyrequired.com>,
        Bart Van Assche <bvanassche@acm.org>,
        David Gow <davidgow@google.com>, linux-mm@kvack.org,
        clang-built-linux@googlegroups.com, linux-hardening@vger.kernel.org
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Precedence: bulk

On Sun, Aug 22, 2021 at 12:51 AM Kees Cook <keescook@chromium.org> wrote:
>
> The core functions of string.c are those that may be implemented by
> per-architecture functions, or overloaded by FORTIFY_SOURCE. As a
> result, it needs to be built with __NO_FORTIFY. Without this, macros

Sorry, is there more info on what exactly __NO_FORTIFY is (and why we
"need" it)?

> will collide with function declarations. This was accidentally working
> due to -ffreestanding (on some architectures). Make this deterministic
> by explicitly setting __NO_FORTIFY and move all the helper functions
> into string_helpers.c so that they gain the fortification coverage they
> had been missing.
>
> Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
>  arch/arm/boot/compressed/string.c     |   1 +
>  arch/s390/lib/string.c                |   3 +
>  arch/x86/boot/compressed/misc.h       |   2 +
>  arch/x86/boot/compressed/pgtable_64.c |   2 +
>  arch/x86/lib/string_32.c              |   1 +
>  lib/string.c                          | 210 +-------------------------
>  lib/string_helpers.c                  | 193 +++++++++++++++++++++++
>  7 files changed, 208 insertions(+), 204 deletions(-)
>
> diff --git a/arch/arm/boot/compressed/string.c b/arch/arm/boot/compressed/string.c
> index 8c0fa276d994..fcc678fce045 100644
> --- a/arch/arm/boot/compressed/string.c
> +++ b/arch/arm/boot/compressed/string.c
> @@ -5,6 +5,7 @@
>   * Small subset of simple string routines
>   */
>
> +#define __NO_FORTIFY
>  #include <linux/string.h>
>
>  /*
> diff --git a/arch/s390/lib/string.c b/arch/s390/lib/string.c
> index cfcdf76d6a95..392fb9f4f4db 100644
> --- a/arch/s390/lib/string.c
> +++ b/arch/s390/lib/string.c
> @@ -8,6 +8,9 @@
>   */
>
>  #define IN_ARCH_STRING_C 1
> +#ifndef __NO_FORTIFY
> +# define __NO_FORTIFY
> +#endif
>
>  #include <linux/types.h>
>  #include <linux/string.h>
> diff --git a/arch/x86/boot/compressed/misc.h b/arch/x86/boot/compressed/misc.h
> index 31139256859f..49bde196da9b 100644
> --- a/arch/x86/boot/compressed/misc.h
> +++ b/arch/x86/boot/compressed/misc.h
> @@ -14,6 +14,8 @@
>  #undef CONFIG_KASAN
>  #undef CONFIG_KASAN_GENERIC
>
> +#define __NO_FORTIFY
> +
>  /* cpu_feature_enabled() cannot be used this early */
>  #define USE_EARLY_PGTABLE_L5
>
> diff --git a/arch/x86/boot/compressed/pgtable_64.c b/arch/x86/boot/compressed/pgtable_64.c
> index 2a78746f5a4c..a1733319a22a 100644
> --- a/arch/x86/boot/compressed/pgtable_64.c
> +++ b/arch/x86/boot/compressed/pgtable_64.c
> @@ -1,3 +1,5 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "misc.h"

^ should we just `#define __NO_FORTIFY` here in pgtable_64.c rather
than set that for a whole header?

>  #include <linux/efi.h>
>  #include <asm/e820/types.h>
>  #include <asm/processor.h>
> diff --git a/arch/x86/lib/string_32.c b/arch/x86/lib/string_32.c
> index d15fdae9656e..53b3f202267c 100644
> --- a/arch/x86/lib/string_32.c
> +++ b/arch/x86/lib/string_32.c
> @@ -11,6 +11,7 @@
>   * strings.
>   */
>
> +#define __NO_FORTIFY
>  #include <linux/string.h>
>  #include <linux/export.h>
>
> diff --git a/lib/string.c b/lib/string.c
> index 77bd0b1d3296..1e6259f263b8 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -6,20 +6,15 @@
>   */
>
>  /*
> - * stupid library routines.. The optimized versions should generally be found
> - * as inline code in <asm-xx/string.h>
> + * This file should be used only for "library" routines that may have
> + * alternative implementations on specific architectures (generally
> + * found in <asm-xx/string.h>), or get overloaded by FORTIFY_SOURCE.
> + * (Specifically, this file is built with __NO_FORTIFY.)
>   *
> - * These are buggy as well..
> - *
> - * * Fri Jun 25 1999, Ingo Oeser <ioe@informatik.tu-chemnitz.de>
> - * -  Added strsep() which will replace strtok() soon (because strsep() is
> - *    reentrant and should be faster). Use only strsep() in new code, please.
> - *
> - * * Sat Feb 09 2002, Jason Thomas <jason@topic.com.au>,
> - *                    Matthew Hawkins <matt@mh.dropbear.id.au>
> - * -  Kissed strtok() goodbye
> + * Other helper functions should live in string_helpers.c.
>   */
>
> +#define __NO_FORTIFY
>  #include <linux/types.h>
>  #include <linux/string.h>
>  #include <linux/ctype.h>
> @@ -237,40 +232,6 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
>  EXPORT_SYMBOL(strscpy);
>  #endif
>
> -/**
> - * strscpy_pad() - Copy a C-string into a sized buffer
> - * @dest: Where to copy the string to
> - * @src: Where to copy the string from
> - * @count: Size of destination buffer
> - *
> - * Copy the string, or as much of it as fits, into the dest buffer.  The
> - * behavior is undefined if the string buffers overlap.  The destination
> - * buffer is always %NUL terminated, unless it's zero-sized.
> - *
> - * If the source string is shorter than the destination buffer, zeros
> - * the tail of the destination buffer.
> - *
> - * For full explanation of why you may want to consider using the
> - * 'strscpy' functions please see the function docstring for strscpy().
> - *
> - * Returns:
> - * * The number of characters copied (not including the trailing %NUL)
> - * * -E2BIG if count is 0 or @src was truncated.
> - */
> -ssize_t strscpy_pad(char *dest, const char *src, size_t count)
> -{
> -       ssize_t written;
> -
> -       written = strscpy(dest, src, count);
> -       if (written < 0 || written == count - 1)
> -               return written;
> -
> -       memset(dest + written + 1, 0, count - written - 1);
> -
> -       return written;
> -}
> -EXPORT_SYMBOL(strscpy_pad);
> -
>  /**
>   * stpcpy - copy a string from src to dest returning a pointer to the new end
>   *          of dest, including src's %NUL-terminator. May overrun dest.
> @@ -513,46 +474,6 @@ char *strnchr(const char *s, size_t count, int c)
>  EXPORT_SYMBOL(strnchr);
>  #endif
>
> -/**
> - * skip_spaces - Removes leading whitespace from @str.
> - * @str: The string to be stripped.
> - *
> - * Returns a pointer to the first non-whitespace character in @str.
> - */
> -char *skip_spaces(const char *str)
> -{
> -       while (isspace(*str))
> -               ++str;
> -       return (char *)str;
> -}
> -EXPORT_SYMBOL(skip_spaces);
> -
> -/**
> - * strim - Removes leading and trailing whitespace from @s.
> - * @s: The string to be stripped.
> - *
> - * Note that the first trailing whitespace is replaced with a %NUL-terminator
> - * in the given string @s. Returns a pointer to the first non-whitespace
> - * character in @s.
> - */
> -char *strim(char *s)
> -{
> -       size_t size;
> -       char *end;
> -
> -       size = strlen(s);
> -       if (!size)
> -               return s;
> -
> -       end = s + size - 1;
> -       while (end >= s && isspace(*end))
> -               end--;
> -       *(end + 1) = '\0';
> -
> -       return skip_spaces(s);
> -}
> -EXPORT_SYMBOL(strim);
> -
>  #ifndef __HAVE_ARCH_STRLEN
>  /**
>   * strlen - Find the length of a string
> @@ -687,101 +608,6 @@ char *strsep(char **s, const char *ct)
>  EXPORT_SYMBOL(strsep);
>  #endif
>
> -/**
> - * sysfs_streq - return true if strings are equal, modulo trailing newline
> - * @s1: one string
> - * @s2: another string
> - *
> - * This routine returns true iff two strings are equal, treating both
> - * NUL and newline-then-NUL as equivalent string terminations.  It's
> - * geared for use with sysfs input strings, which generally terminate
> - * with newlines but are compared against values without newlines.
> - */
> -bool sysfs_streq(const char *s1, const char *s2)
> -{
> -       while (*s1 && *s1 == *s2) {
> -               s1++;
> -               s2++;
> -       }
> -
> -       if (*s1 == *s2)
> -               return true;
> -       if (!*s1 && *s2 == '\n' && !s2[1])
> -               return true;
> -       if (*s1 == '\n' && !s1[1] && !*s2)
> -               return true;
> -       return false;
> -}
> -EXPORT_SYMBOL(sysfs_streq);
> -
> -/**
> - * match_string - matches given string in an array
> - * @array:     array of strings
> - * @n:         number of strings in the array or -1 for NULL terminated arrays
> - * @string:    string to match with
> - *
> - * This routine will look for a string in an array of strings up to the
> - * n-th element in the array or until the first NULL element.
> - *
> - * Historically the value of -1 for @n, was used to search in arrays that
> - * are NULL terminated. However, the function does not make a distinction
> - * when finishing the search: either @n elements have been compared OR
> - * the first NULL element was found.
> - *
> - * Return:
> - * index of a @string in the @array if matches, or %-EINVAL otherwise.
> - */
> -int match_string(const char * const *array, size_t n, const char *string)
> -{
> -       int index;
> -       const char *item;
> -
> -       for (index = 0; index < n; index++) {
> -               item = array[index];
> -               if (!item)
> -                       break;
> -               if (!strcmp(item, string))
> -                       return index;
> -       }
> -
> -       return -EINVAL;
> -}
> -EXPORT_SYMBOL(match_string);
> -
> -/**
> - * __sysfs_match_string - matches given string in an array
> - * @array: array of strings
> - * @n: number of strings in the array or -1 for NULL terminated arrays
> - * @str: string to match with
> - *
> - * Returns index of @str in the @array or -EINVAL, just like match_string().
> - * Uses sysfs_streq instead of strcmp for matching.
> - *
> - * This routine will look for a string in an array of strings up to the
> - * n-th element in the array or until the first NULL element.
> - *
> - * Historically the value of -1 for @n, was used to search in arrays that
> - * are NULL terminated. However, the function does not make a distinction
> - * when finishing the search: either @n elements have been compared OR
> - * the first NULL element was found.
> - */
> -int __sysfs_match_string(const char * const *array, size_t n, const char *str)
> -{
> -       const char *item;
> -       int index;
> -
> -       for (index = 0; index < n; index++) {
> -               item = array[index];
> -               if (!item)
> -                       break;
> -               if (sysfs_streq(item, str))
> -                       return index;
> -       }?
> -
> -       return -EINVAL;
> -}
> -EXPORT_SYMBOL(__sysfs_match_string);
> -

are memset16, memset32, and memset64 worth moving as well? Also,
memscan(), check_bytes(), memchr_inv()?

>  #ifndef __HAVE_ARCH_MEMSET
>  /**
>   * memset - Fill a region of memory with the given value
> @@ -1125,27 +951,3 @@ void *memchr_inv(const void *start, int c, size_t bytes)
>         return check_bytes8(start, value, bytes % 8);
>  }
>  EXPORT_SYMBOL(memchr_inv);
> -
> -/**
> - * strreplace - Replace all occurrences of character in string.
> - * @s: The string to operate on.
> - * @old: The character being replaced.
> - * @new: The character @old is replaced with.
> - *
> - * Returns pointer to the nul byte at the end of @s.
> - */
> -char *strreplace(char *s, char old, char new)
> -{
> -       for (; *s; ++s)
> -               if (*s == old)
> -                       *s = new;
> -       return s;
> -}
> -EXPORT_SYMBOL(strreplace);
> -
> -void fortify_panic(const char *name)
> -{
> -       pr_emerg("detected buffer overflow in %s\n", name);
> -       BUG();
> -}
> -EXPORT_SYMBOL(fortify_panic);
> diff --git a/lib/string_helpers.c b/lib/string_helpers.c
> index 5a35c7e16e96..e9433caab217 100644
> --- a/lib/string_helpers.c
> +++ b/lib/string_helpers.c
> @@ -692,3 +692,196 @@ void kfree_strarray(char **array, size_t n)
>         kfree(array);
>  }
>  EXPORT_SYMBOL_GPL(kfree_strarray);
> +
> +/**
> + * strscpy_pad() - Copy a C-string into a sized buffer
> + * @dest: Where to copy the string to
> + * @src: Where to copy the string from
> + * @count: Size of destination buffer
> + *
> + * Copy the string, or as much of it as fits, into the dest buffer.  The
> + * behavior is undefined if the string buffers overlap.  The destination
> + * buffer is always %NUL terminated, unless it's zero-sized.
> + *
> + * If the source string is shorter than the destination buffer, zeros
> + * the tail of the destination buffer.
> + *
> + * For full explanation of why you may want to consider using the
> + * 'strscpy' functions please see the function docstring for strscpy().
> + *
> + * Returns:
> + * * The number of characters copied (not including the trailing %NUL)
> + * * -E2BIG if count is 0 or @src was truncated.
> + */
> +ssize_t strscpy_pad(char *dest, const char *src, size_t count)
> +{
> +       ssize_t written;
> +
> +       written = strscpy(dest, src, count);
> +       if (written < 0 || written == count - 1)
> +               return written;
> +
> +       memset(dest + written + 1, 0, count - written - 1);
> +
> +       return written;
> +}
> +EXPORT_SYMBOL(strscpy_pad);
> +
> +/**
> + * skip_spaces - Removes leading whitespace from @str.
> + * @str: The string to be stripped.
> + *
> + * Returns a pointer to the first non-whitespace character in @str.
> + */
> +char *skip_spaces(const char *str)
> +{
> +       while (isspace(*str))
> +               ++str;
> +       return (char *)str;
> +}
> +EXPORT_SYMBOL(skip_spaces);
> +
> +/**
> + * strim - Removes leading and trailing whitespace from @s.
> + * @s: The string to be stripped.
> + *
> + * Note that the first trailing whitespace is replaced with a %NUL-terminator
> + * in the given string @s. Returns a pointer to the first non-whitespace
> + * character in @s.
> + */
> +char *strim(char *s)
> +{
> +       size_t size;
> +       char *end;
> +
> +       size = strlen(s);
> +       if (!size)
> +               return s;
> +
> +       end = s + size - 1;
> +       while (end >= s && isspace(*end))
> +               end--;
> +       *(end + 1) = '\0';
> +
> +       return skip_spaces(s);
> +}
> +EXPORT_SYMBOL(strim);
> +
> +/**
> + * sysfs_streq - return true if strings are equal, modulo trailing newline
> + * @s1: one string
> + * @s2: another string
> + *
> + * This routine returns true iff two strings are equal, treating both
> + * NUL and newline-then-NUL as equivalent string terminations.  It's
> + * geared for use with sysfs input strings, which generally terminate
> + * with newlines but are compared against values without newlines.
> + */
> +bool sysfs_streq(const char *s1, const char *s2)
> +{
> +       while (*s1 && *s1 == *s2) {
> +               s1++;
> +               s2++;
> +       }
> +
> +       if (*s1 == *s2)
> +               return true;
> +       if (!*s1 && *s2 == '\n' && !s2[1])
> +               return true;
> +       if (*s1 == '\n' && !s1[1] && !*s2)
> +               return true;
> +       return false;
> +}
> +EXPORT_SYMBOL(sysfs_streq);
> +
> +/**
> + * match_string - matches given string in an array
> + * @array:     array of strings
> + * @n:         number of strings in the array or -1 for NULL terminated arrays
> + * @string:    string to match with
> + *
> + * This routine will look for a string in an array of strings up to the
> + * n-th element in the array or until the first NULL element.
> + *
> + * Historically the value of -1 for @n, was used to search in arrays that
> + * are NULL terminated. However, the function does not make a distinction
> + * when finishing the search: either @n elements have been compared OR
> + * the first NULL element was found.
> + *
> + * Return:
> + * index of a @string in the @array if matches, or %-EINVAL otherwise.
> + */
> +int match_string(const char * const *array, size_t n, const char *string)
> +{
> +       int index;
> +       const char *item;
> +
> +       for (index = 0; index < n; index++) {
> +               item = array[index];
> +               if (!item)
> +                       break;
> +               if (!strcmp(item, string))
> +                       return index;
> +       }
> +
> +       return -EINVAL;
> +}
> +EXPORT_SYMBOL(match_string);
> +
> +/**
> + * __sysfs_match_string - matches given string in an array
> + * @array: array of strings
> + * @n: number of strings in the array or -1 for NULL terminated arrays
> + * @str: string to match with
> + *
> + * Returns index of @str in the @array or -EINVAL, just like match_string().
> + * Uses sysfs_streq instead of strcmp for matching.
> + *
> + * This routine will look for a string in an array of strings up to the
> + * n-th element in the array or until the first NULL element.
> + *
> + * Historically the value of -1 for @n, was used to search in arrays that
> + * are NULL terminated. However, the function does not make a distinction
> + * when finishing the search: either @n elements have been compared OR
> + * the first NULL element was found.
> + */
> +int __sysfs_match_string(const char * const *array, size_t n, const char *str)
> +{
> +       const char *item;
> +       int index;
> +
> +       for (index = 0; index < n; index++) {
> +               item = array[index];
> +               if (!item)
> +                       break;
> +               if (sysfs_streq(item, str))
> +                       return index;
> +       }
> +
> +       return -EINVAL;
> +}
> +EXPORT_SYMBOL(__sysfs_match_string);
> +
> +/**
> + * strreplace - Replace all occurrences of character in string.
> + * @s: The string to operate on.
> + * @old: The character being replaced.
> + * @new: The character @old is replaced with.
> + *
> + * Returns pointer to the nul byte at the end of @s.
> + */
> +char *strreplace(char *s, char old, char new)
> +{
> +       for (; *s; ++s)
> +               if (*s == old)
> +                       *s = new;
> +       return s;
> +}
> +EXPORT_SYMBOL(strreplace);
> +
> +void fortify_panic(const char *name)
> +{
> +       pr_emerg("detected buffer overflow in %s\n", name);
> +       BUG();
> +}
> +EXPORT_SYMBOL(fortify_panic);
> --


-- 
Thanks,
~Nick Desaulniers