Re: [PATCH mm v3 26/38] kasan, vmalloc: don't unpoison VM_ALLOC pages before mapping

[Alexander Potapenko <glider@google.com>]

On Mon, Dec 13, 2021 at 10:54 PM <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Make KASAN unpoison vmalloc mappings after that have been mapped in
> when it's possible: for vmalloc() (indentified via VM_ALLOC) and
> vm_map_ram().

The subject says "don't unpoison VM_ALLOC pages", whereas the
description says "unpoison VM_ALLOC pages", or am I missing something?

> The reasons for this are:
>
> - For vmalloc() and vm_map_ram(): pages don't get unpoisoned in case
>   mapping them fails.
> - For vmalloc(): HW_TAGS KASAN needs pages to be mapped to set tags via
>   kasan_unpoison_vmalloc().
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
>
> ---
>
> Changes v2->v3:
> - Update patch description.
> ---
>  mm/vmalloc.c | 26 ++++++++++++++++++++++----
>  1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 58bd2f7f86d7..9a6862e274df 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2208,14 +2208,15 @@ void *vm_map_ram(struct page **pages, unsigned int count, int node)
>                 mem = (void *)addr;
>         }
>
> -       mem = kasan_unpoison_vmalloc(mem, size);
> -
>         if (vmap_pages_range(addr, addr + size, PAGE_KERNEL,
>                                 pages, PAGE_SHIFT) < 0) {
>                 vm_unmap_ram(mem, count);
>                 return NULL;
>         }
>
> +       /* Mark the pages as accessible after they were mapped in. */
> +       mem = kasan_unpoison_vmalloc(mem, size);
> +
>         return mem;
>  }
>  EXPORT_SYMBOL(vm_map_ram);
> @@ -2443,7 +2444,14 @@ static struct vm_struct *__get_vm_area_node(unsigned long size,
>
>         setup_vmalloc_vm(area, va, flags, caller);
>
> -       area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
> +       /*
> +        * For VM_ALLOC mappings, __vmalloc_node_range() mark the pages as
> +        * accessible after they are mapped in.
> +        * Otherwise, as the pages can be mapped outside of vmalloc code,
> +        * mark them now as a best-effort approach.
> +        */
> +       if (!(flags & VM_ALLOC))
> +               area->addr = kasan_unpoison_vmalloc(area->addr, requested_size);
>
>         return area;
>  }
> @@ -3104,6 +3112,12 @@ void *__vmalloc_node_range(unsigned long size, unsigned long align,
>         if (!addr)
>                 goto fail;
>
> +       /*
> +        * Mark the pages for VM_ALLOC mappings as accessible after they were
> +        * mapped in.
> +        */
> +       addr = kasan_unpoison_vmalloc(addr, real_size);
> +
>         /*
>          * In this function, newly allocated vm_struct has VM_UNINITIALIZED
>          * flag. It means that vm_struct is not fully initialized.
> @@ -3799,7 +3813,11 @@ struct vm_struct **pcpu_get_vm_areas(const unsigned long *offsets,
>         }
>         spin_unlock(&vmap_area_lock);
>
> -       /* mark allocated areas as accessible */
> +       /*
> +        * Mark allocated areas as accessible.
> +        * As the pages are mapped outside of vmalloc code,
> +        * mark them now as a best-effort approach.
> +        */
>         for (area = 0; area < nr_vms; area++)
>                 vms[area]->addr = kasan_unpoison_vmalloc(vms[area]->addr,
>                                                          vms[area]->size);
> --
> 2.25.1
>
> --
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-- 
Alexander Potapenko
Software Engineer

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