kernel/linux.git/lib/string.c, branch v6.6.132

string: Add load_unaligned_zeropad() code path to sized_strscpy()

2025-04-25T08:45:50+00:00

commit d94c12bd97d567de342fd32599e7cd9e50bfa140 upstream. The call to read_word_at_a_time() in sized_strscpy() is problematic with MTE because it may trigger a tag check fault when reading across a tag granule (16 bytes) boundary. To make this code MTE compatible, let's start using load_unaligned_zeropad() on architectures where it is available (i.e. architectures that define CONFIG_DCACHE_WORD_ACCESS). Because load_unaligned_zeropad() takes care of page boundaries as well as tag granule boundaries, also disable the code preventing crossing page boundaries when using load_unaligned_zeropad(). Signed-off-by: Peter Collingbourne Link: https://linux-review.googlesource.com/id/If4b22e43b5a4ca49726b4bf98ada827fdf755548 Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS") Cc: stable@vger.kernel.org Reviewed-by: Catalin Marinas Link: https://lore.kernel.org/r/20250403000703.2584581-2-pcc@google.com Signed-off-by: Kees Cook Signed-off-by: Greg Kroah-Hartman

string: use __builtin_memcpy() in strlcpy/strlcat

2023-06-01T18:24:50+00:00

lib/string.c is built with -ffreestanding, which prevents the compiler from replacing certain functions with calls to their library versions. On the other hand, this also prevents Clang and GCC from instrumenting calls to memcpy() when building with KASAN, KCSAN or KMSAN: - KASAN normally replaces memcpy() with __asan_memcpy() with the additional cc-param,asan-kernel-mem-intrinsic-prefix=1; - KCSAN and KMSAN replace memcpy() with __tsan_memcpy() and __msan_memcpy() by default. To let the tools catch memory accesses from strlcpy/strlcat, replace the calls to memcpy() with __builtin_memcpy(), which KASAN, KCSAN and KMSAN are able to replace even in -ffreestanding mode. This preserves the behavior in normal builds (__builtin_memcpy() ends up being replaced with memcpy()), and does not introduce new instrumentation in unwanted places, as strlcpy/strlcat are already instrumented. Suggested-by: Marco Elver Signed-off-by: Alexander Potapenko Reviewed-by: Marco Elver Link: https://lore.kernel.org/all/20230224085942.1791837-1-elver@google.com/ Acked-by: Kees Cook Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20230530083911.1104336-1-glider@google.com

lib/string: Use strchr() in strpbrk()

2023-01-27T19:42:57+00:00

Use strchr() instead of open coding it as it's done elsewhere in the same file. Either we will have similar to what it was or possibly better performance in case architecture implements its own strchr(). Memory wise on x86_64 bloat-o-meter shows the following Function old new delta strsep 111 102 -9 Total: Before=2763, After=2754, chg -0.33% Signed-off-by: Andy Shevchenko Signed-off-by: Kees Cook Link: https://lore.kernel.org/r/20230127155135.27153-1-andriy.shevchenko@linux.intel.com

string: Rewrite and add more kern-doc for the str*() functions

2022-10-28T23:07:57+00:00

While there were varying degrees of kern-doc for various str*()-family functions, many needed updating and clarification, or to just be entirely written. Update (and relocate) existing kern-doc and add missing functions, sadly shaking my head at how many times I have written "Do not use this function". Include the results in the core kernel API doc. Cc: Bagas Sanjaya Cc: Andy Shevchenko Cc: Rasmus Villemoes Cc: Andrew Morton Cc: linux-hardening@vger.kernel.org Tested-by: Akira Yokosawa Link: https://lore.kernel.org/lkml/9b0cf584-01b3-3013-b800-1ef59fe82476@gmail.com Signed-off-by: Kees Cook

kmsan: disable strscpy() optimization under KMSAN

2022-10-03T21:03:22+00:00

Disable the efficient 8-byte reading under KMSAN to avoid false positives. Link: https://lkml.kernel.org/r/20220915150417.722975-26-glider@google.com Signed-off-by: Alexander Potapenko Cc: Alexander Viro Cc: Alexei Starovoitov Cc: Andrey Konovalov Cc: Andrey Konovalov Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Christoph Hellwig Cc: Christoph Lameter Cc: David Rientjes Cc: Dmitry Vyukov Cc: Eric Biggers Cc: Eric Biggers Cc: Eric Dumazet Cc: Greg Kroah-Hartman Cc: Herbert Xu Cc: Ilya Leoshkevich Cc: Ingo Molnar Cc: Jens Axboe Cc: Joonsoo Kim Cc: Kees Cook Cc: Marco Elver Cc: Mark Rutland Cc: Matthew Wilcox Cc: Michael S. Tsirkin Cc: Pekka Enberg Cc: Peter Zijlstra Cc: Petr Mladek Cc: Stephen Rothwell Cc: Steven Rostedt Cc: Thomas Gleixner Cc: Vasily Gorbik Cc: Vegard Nossum Cc: Vlastimil Babka Signed-off-by: Andrew Morton

lib/string.c: simplify str[c]spn

2022-04-29T21:38:01+00:00

Use strchr(), which makes them a lot shorter, and more obviously symmetric in their treatment of accept/reject. It also saves a little bit of .text; bloat-o-meter for an arm build says Function old new delta strcspn 92 76 -16 strspn 108 76 -32 While here, also remove a stray empty line before EXPORT_SYMBOL(). Link: https://lkml.kernel.org/r/20220328224119.3003834-2-linux@rasmusvillemoes.dk Signed-off-by: Rasmus Villemoes Cc: Andy Shevchenko Signed-off-by: Andrew Morton

lib/string: Move helper functions out of string.c

2021-09-25T15:20:49+00:00

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 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. Cc: Andrew Morton Cc: Nick Desaulniers Cc: Andy Lavr Cc: Nathan Chancellor Cc: Alexey Dobriyan Cc: Stephen Rothwell Cc: Bartosz Golaszewski Acked-by: Andy Shevchenko Signed-off-by: Kees Cook

string: improve default out-of-line memcmp() implementation

2021-08-30T14:50:56+00:00

This just does the "if the architecture does efficient unaligned handling, start the memcmp using 'unsigned long' accesses", since Nikolay Borisov found a load that cares. This is basically the minimal patch, and limited to architectures that are known to not have slow unaligned handling. We've had the stupid byte-at-a-time version forever, and nobody has ever even noticed before, so let's keep the fix minimal. A potential further improvement would be to align one of the sources in order to at least minimize unaligned cases, but the only real case of bigger memcmp() users seems to be the FIDEDUPERANGE ioctl(). As David Sterba says, the dedupe ioctl is typically called on ranges spanning many pages so the common case will all be page-aligned anyway. All the relevant architectures select HAVE_EFFICIENT_UNALIGNED_ACCESS, so I'm not going to worry about the combination of a very rare use-case and a rare architecture until somebody actually hits it. Particularly since Nikolay also tested the more complex patch with extra alignment handling code, and it only added overhead. Link: https://lore.kernel.org/lkml/20210721135926.602840-1-nborisov@suse.com/ Reported-by: Nikolay Borisov Cc: David Sterba Signed-off-by: Linus Torvalds

lib: memscan() fixlet

2021-07-01T18:06:05+00:00

Generic version doesn't trucate second argument to char. Older brother memchr() does as do s390, sparc and i386 assembly versions. Fortunately, no code passes c >= 256. Link: https://lkml.kernel.org/r/YLv4cCf0t5UPdyK+@localhost.localdomain Signed-off-by: Alexey Dobriyan Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

lib/string: remove unnecessary #undefs

2020-12-16T06:46:16+00:00

A few architecture specific string.h functions used to be implemented in terms of preprocessor defines to the corresponding compiler builtins. Since this is no longer the case, remove unused #undefs. Only memcmp is still defined in terms of builtins for a few arches. Link: https://github.com/ClangBuiltLinux/linux/issues/428 Link: https://lkml.kernel.org/r/20201120041113.89382-1-ndesaulniers@google.com Fixes: 5f074f3e192f ("lib/string.c: implement a basic bcmp") Signed-off-by: Nick Desaulniers Cc: Andy Shevchenko Cc: Yury Norov Cc: Alexandru Ardelean Cc: Nathan Chancellor Cc: Masahiro Yamada Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds