[PATCH 27/31] kasan, vmalloc: add vmalloc support to HW_TAGS

[Marco Elver]

On Tue, Nov 30, 2021 at 11:08PM +0100, andrey.konovalov at linux.dev wrote:
> From: Andrey Konovalov <andreyknvl at google.com>
> 
> This patch adds vmalloc tagging support to HW_TAGS KASAN.
> 
> The key difference between HW_TAGS and the other two KASAN modes
> when it comes to vmalloc: HW_TAGS KASAN can only assign tags to
> physical memory. The other two modes have shadow memory covering
> every mapped virtual memory region.
> 
> This patch makes __kasan_unpoison_vmalloc() for HW_TAGS KASAN:
> 
> - Skip non-VM_ALLOC mappings as HW_TAGS KASAN can only tag a single
>   mapping of normal physical memory; see the comment in the function.
> - Generate a random tag, tag the returned pointer and the allocation.
> - Propagate the tag into the page stucts to allow accesses through
>   page_address(vmalloc_to_page()).
> 
> The rest of vmalloc-related KASAN hooks are not needed:
> 
> - The shadow-related ones are fully skipped.
> - __kasan_poison_vmalloc() is kept as a no-op with a comment.
> 
> Poisoning of physical pages that are backing vmalloc() allocations
> is skipped via __GFP_SKIP_KASAN_UNPOISON: __kasan_unpoison_vmalloc()
> poisons them instead.
> 
> Signed-off-by: Andrey Konovalov <andreyknvl at google.com>
> Co-developed-by: Vincenzo Frascino <vincenzo.frascino at arm.com>

This is missing a Signed-off-by from Vincenzo.