[Bug sanitizer/85230] asan: false positives in kernel on allocas

["dvyukov at google dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85230

--- Comment #1 from Dmitry Vyukov <dvyukov at google dot com> ---
I am also looking at kernel callback implementation, maybe they disagree with
compiler as to what's actually passed as arguments:


/* Emitted by compiler to poison alloca()ed objects. */
void __asan_alloca_poison(unsigned long addr, size_t size)
{
        size_t rounded_up_size = round_up(size, KASAN_SHADOW_SCALE_SIZE);
        size_t padding_size = round_up(size, KASAN_ALLOCA_REDZONE_SIZE) -
                        rounded_up_size;
        size_t rounded_down_size = round_down(size, KASAN_SHADOW_SCALE_SIZE);

        const void *left_redzone = (const void *)(addr -
                        KASAN_ALLOCA_REDZONE_SIZE);
        const void *right_redzone = (const void *)(addr + rounded_up_size);

        WARN_ON(!IS_ALIGNED(addr, KASAN_ALLOCA_REDZONE_SIZE));

        kasan_unpoison_shadow((const void *)(addr + rounded_down_size),
                              size - rounded_down_size);
        kasan_poison_shadow(left_redzone, KASAN_ALLOCA_REDZONE_SIZE,
                        KASAN_ALLOCA_LEFT);
        kasan_poison_shadow(right_redzone,
                        padding_size + KASAN_ALLOCA_REDZONE_SIZE,
                        KASAN_ALLOCA_RIGHT);
}
EXPORT_SYMBOL(__asan_alloca_poison);

/* Emitted by compiler to unpoison alloca()ed areas when the stack unwinds. */
void __asan_allocas_unpoison(const void *stack_top, const void *stack_bottom)
{
        if (unlikely(!stack_top || stack_top > stack_bottom))
                return;

        kasan_unpoison_shadow(stack_top, stack_bottom - stack_top);
}
EXPORT_SYMBOL(__asan_allocas_unpoison);