6.12-stable review patch. If anyone has any objections, please let me know.
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From: Peter Collingbourne pcc@google.com
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 pcc@google.com Link: https://linux-review.googlesource.com/id/If4b22e43b5a4ca49726b4bf98ada827fdf... Fixes: 94ab5b61ee16 ("kasan, arm64: enable CONFIG_KASAN_HW_TAGS") Cc: stable@vger.kernel.org Reviewed-by: Catalin Marinas catalin.marinas@arm.com Link: https://lore.kernel.org/r/20250403000703.2584581-2-pcc@google.com Signed-off-by: Kees Cook kees@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- lib/string.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)
--- a/lib/string.c +++ b/lib/string.c @@ -113,6 +113,7 @@ ssize_t sized_strscpy(char *dest, const if (count == 0 || WARN_ON_ONCE(count > INT_MAX)) return -E2BIG;
+#ifndef CONFIG_DCACHE_WORD_ACCESS #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS /* * If src is unaligned, don't cross a page boundary, @@ -128,11 +129,13 @@ ssize_t sized_strscpy(char *dest, const if (((long) dest | (long) src) & (sizeof(long) - 1)) max = 0; #endif +#endif
/* - * read_word_at_a_time() below may read uninitialized bytes after the - * trailing zero and use them in comparisons. Disable this optimization - * under KMSAN to prevent false positive reports. + * load_unaligned_zeropad() or read_word_at_a_time() below may read + * uninitialized bytes after the trailing zero and use them in + * comparisons. Disable this optimization under KMSAN to prevent + * false positive reports. */ if (IS_ENABLED(CONFIG_KMSAN)) max = 0; @@ -140,7 +143,11 @@ ssize_t sized_strscpy(char *dest, const while (max >= sizeof(unsigned long)) { unsigned long c, data;
+#ifdef CONFIG_DCACHE_WORD_ACCESS + c = load_unaligned_zeropad(src+res); +#else c = read_word_at_a_time(src+res); +#endif if (has_zero(c, &data, &constants)) { data = prep_zero_mask(c, data, &constants); data = create_zero_mask(data);