Re: [PATCH v2 2/4] mm: kmsan: handle alloc failures in kmsan_ioremap_page_range()

[Marco Elver]

On Thu, 13 Apr 2023 at 15:12, Alexander Potapenko <glider@xxxxxxxxxx> wrote:
>
> Similarly to kmsan_vmap_pages_range_noflush(),
> kmsan_ioremap_page_range() must also properly handle allocation/mapping
> failures. In the case of such, it must clean up the already created
> metadata mappings and return an error code, so that the error can be
> propagated to ioremap_page_range(). Without doing so, KMSAN may silently
> fail to bring the metadata for the page range into a consistent state,
> which will result in user-visible crashes when trying to access them.
>
> Reported-by: Dipanjan Das <mail.dipanjan.das@xxxxxxxxx>
> Link: https://lore.kernel.org/linux-mm/CANX2M5ZRrRA64k0hOif02TjmY9kbbO2aCBPyq79es34RXZ=cAw@xxxxxxxxxxxxxx/
> Fixes: b073d7f8aee4 ("mm: kmsan: maintain KMSAN metadata for page operations")
> Signed-off-by: Alexander Potapenko <glider@xxxxxxxxxx>

Reviewed-by: Marco Elver <elver@xxxxxxxxxx>

> ---
> v2:
>  -- updated patch description as requested by Andrew Morton
>  -- check the return value of __vmap_pages_range_noflush(), as suggested by Dipanjan Das
>  -- return 0 from the inline version of kmsan_ioremap_page_range()
>     (spotted by kernel test robot <lkp@xxxxxxxxx>)
> ---
>  include/linux/kmsan.h | 19 ++++++++-------
>  mm/kmsan/hooks.c      | 55 ++++++++++++++++++++++++++++++++++++-------
>  mm/vmalloc.c          |  4 ++--
>  3 files changed, 59 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/kmsan.h b/include/linux/kmsan.h
> index c7ff3aefc5a13..30b17647ce3c7 100644
> --- a/include/linux/kmsan.h
> +++ b/include/linux/kmsan.h
> @@ -160,11 +160,12 @@ void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end);
>   * @page_shift:        page_shift argument passed to vmap_range_noflush().
>   *
>   * KMSAN creates new metadata pages for the physical pages mapped into the
> - * virtual memory.
> + * virtual memory. Returns 0 on success, callers must check for non-zero return
> + * value.
>   */
> -void kmsan_ioremap_page_range(unsigned long addr, unsigned long end,
> -                             phys_addr_t phys_addr, pgprot_t prot,
> -                             unsigned int page_shift);
> +int kmsan_ioremap_page_range(unsigned long addr, unsigned long end,
> +                            phys_addr_t phys_addr, pgprot_t prot,
> +                            unsigned int page_shift);
>
>  /**
>   * kmsan_iounmap_page_range() - Notify KMSAN about a iounmap_page_range() call.
> @@ -296,12 +297,12 @@ static inline void kmsan_vunmap_range_noflush(unsigned long start,
>  {
>  }
>
> -static inline void kmsan_ioremap_page_range(unsigned long start,
> -                                           unsigned long end,
> -                                           phys_addr_t phys_addr,
> -                                           pgprot_t prot,
> -                                           unsigned int page_shift)
> +static inline int kmsan_ioremap_page_range(unsigned long start,
> +                                          unsigned long end,
> +                                          phys_addr_t phys_addr, pgprot_t prot,
> +                                          unsigned int page_shift)
>  {
> +       return 0;
>  }
>
>  static inline void kmsan_iounmap_page_range(unsigned long start,
> diff --git a/mm/kmsan/hooks.c b/mm/kmsan/hooks.c
> index 3807502766a3e..ec0da72e65aa0 100644
> --- a/mm/kmsan/hooks.c
> +++ b/mm/kmsan/hooks.c
> @@ -148,35 +148,74 @@ void kmsan_vunmap_range_noflush(unsigned long start, unsigned long end)
>   * into the virtual memory. If those physical pages already had shadow/origin,
>   * those are ignored.
>   */
> -void kmsan_ioremap_page_range(unsigned long start, unsigned long end,
> -                             phys_addr_t phys_addr, pgprot_t prot,
> -                             unsigned int page_shift)
> +int kmsan_ioremap_page_range(unsigned long start, unsigned long end,
> +                            phys_addr_t phys_addr, pgprot_t prot,
> +                            unsigned int page_shift)
>  {
>         gfp_t gfp_mask = GFP_KERNEL | __GFP_ZERO;
>         struct page *shadow, *origin;
>         unsigned long off = 0;
> -       int nr;
> +       int nr, err = 0, clean = 0, mapped;
>
>         if (!kmsan_enabled || kmsan_in_runtime())
> -               return;
> +               return 0;
>
>         nr = (end - start) / PAGE_SIZE;
>         kmsan_enter_runtime();
> -       for (int i = 0; i < nr; i++, off += PAGE_SIZE) {
> +       for (int i = 0; i < nr; i++, off += PAGE_SIZE, clean = i) {
>                 shadow = alloc_pages(gfp_mask, 1);
>                 origin = alloc_pages(gfp_mask, 1);
> -               __vmap_pages_range_noflush(
> +               if (!shadow || !origin) {
> +                       err = -ENOMEM;
> +                       goto ret;
> +               }
> +               mapped = __vmap_pages_range_noflush(
>                         vmalloc_shadow(start + off),
>                         vmalloc_shadow(start + off + PAGE_SIZE), prot, &shadow,
>                         PAGE_SHIFT);
> -               __vmap_pages_range_noflush(
> +               if (mapped) {
> +                       err = mapped;
> +                       goto ret;
> +               }
> +               shadow = NULL;
> +               mapped = __vmap_pages_range_noflush(
>                         vmalloc_origin(start + off),
>                         vmalloc_origin(start + off + PAGE_SIZE), prot, &origin,
>                         PAGE_SHIFT);
> +               if (mapped) {
> +                       __vunmap_range_noflush(
> +                               vmalloc_shadow(start + off),
> +                               vmalloc_shadow(start + off + PAGE_SIZE));
> +                       err = mapped;
> +                       goto ret;
> +               }
> +               origin = NULL;
> +       }
> +       /* Page mapping loop finished normally, nothing to clean up. */
> +       clean = 0;
> +
> +ret:
> +       if (clean > 0) {
> +               /*
> +                * Something went wrong. Clean up shadow/origin pages allocated
> +                * on the last loop iteration, then delete mappings created
> +                * during the previous iterations.
> +                */
> +               if (shadow)
> +                       __free_pages(shadow, 1);
> +               if (origin)
> +                       __free_pages(origin, 1);
> +               __vunmap_range_noflush(
> +                       vmalloc_shadow(start),
> +                       vmalloc_shadow(start + clean * PAGE_SIZE));
> +               __vunmap_range_noflush(
> +                       vmalloc_origin(start),
> +                       vmalloc_origin(start + clean * PAGE_SIZE));
>         }
>         flush_cache_vmap(vmalloc_shadow(start), vmalloc_shadow(end));
>         flush_cache_vmap(vmalloc_origin(start), vmalloc_origin(end));
>         kmsan_leave_runtime();
> +       return err;
>  }
>
>  void kmsan_iounmap_page_range(unsigned long start, unsigned long end)
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 1355d95cce1ca..31ff782d368b0 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -313,8 +313,8 @@ int ioremap_page_range(unsigned long addr, unsigned long end,
>                                  ioremap_max_page_shift);
>         flush_cache_vmap(addr, end);
>         if (!err)
> -               kmsan_ioremap_page_range(addr, end, phys_addr, prot,
> -                                        ioremap_max_page_shift);
> +               err = kmsan_ioremap_page_range(addr, end, phys_addr, prot,
> +                                              ioremap_max_page_shift);
>         return err;
>  }
>
> --
> 2.40.0.577.gac1e443424-goog
>