On Fri, Sep 5, 2025 at 7:12 PM Andrey Ryabinin <[email protected]> wrote: > > > But have you tried running kasan=off + CONFIG_KASAN_STACK=y + > > CONFIG_VMAP_STACK=y (+ CONFIG_KASAN_VMALLOC=y)? I would expect this > > should causes crashes, as the early shadow is mapped as read-only and > > the inline stack instrumentation will try writing into it (or do the > > writes into the early shadow somehow get ignored?..). > > > > It's not read-only, otherwise we would crash very early before full shadow > setup and won't be able to boot at all. So writes still happen, and shadow > checked, but reports are disabled.
Hm, I thought it worked like that, but then what threw me off just now was seeing that zero_pte_populate()->pte_wrprotect() (on arm64) resets the PTE_WRITE bit and sets the PTE_RDONLY bit. So I thought the kasan_early_shadow_page is marked as read-only and then the instrumentation is disabled for all early code that might write into the page before the proper shadow is set up. Or am I reading this bit-setting code wrong?
