On Wed, Mar 25, 2020 at 5:14 PM <glider@xxxxxxxxxx> wrote:
>
> Disable the efficient 8-byte reading under KMSAN to avoid false positives.
Another user of read_word_at_a_time() is dentry_string_cmp() in
dcache.c, should we disable it there as well?
>
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>
> To: Alexander Potapenko <glider@xxxxxxxxxx>
> Cc: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
> Cc: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxxx>
> Cc: linux-mm@xxxxxxxxx
>
> ---
>
> v4:
> - actually disable the optimization under KMSAN via max=0
> - use IS_ENABLED as requested by Marco Elver
>
> Change-Id: I25d1acf5c3df6eff85894cd94f5ddbe93308271c
> ---
> lib/string.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/lib/string.c b/lib/string.c
> index 6012c385fb314..fec929e70f1a5 100644
> --- a/lib/string.c
> +++ b/lib/string.c
> @@ -202,6 +202,14 @@ ssize_t strscpy(char *dest, const char *src, size_t count)
> max = 0;
> #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.
> + */
> + if (IS_ENABLED(CONFIG_KMSAN))
> + max = 0;
> +
> while (max >= sizeof(unsigned long)) {
> unsigned long c, data;
>
> --
> 2.25.1.696.g5e7596f4ac-goog
>
