Subject: [linux-next PATCH] arm64: fix kernel crash with 48-bit VA and 64KB granule

From: [email-masked] (Dennis Chen)
Date: Wed, 6 Jan 2016 10:55:21 +0800

On Tue, Jan 05, 2016 at 03:44:44PM +0000, Will Deacon wrote:
> On Tue, Jan 05, 2016 at 01:47:11PM +0100, Ard Biesheuvel wrote:
> > On 5 January 2016 at 13:31, Will Deacon <[email-masked]> wrote:
> > > On Tue, Jan 05, 2016 at 08:36:39AM +0100, Ard Biesheuvel wrote:
> > >> The issue only occurs when PGD_SIZE != PAGE_SIZE, which is why I did
> > >> not see it myself. I only tested with 4k/39-bits and 64k/42-bits IIRC,
> > >> since the series this is part of primarily concerns ARM not arm64.
> > >>
> > >> Anyway, shuffling init ordering is my least favorite way of fixing
> > >> bugs. Since only ARM requires pgd_alloc() (for the kernel mappings),
> > >> we could also simply factor out pgd_alloc() into efi_pgd_alloc(), and
> > >> define it to mean '__get_free_page(PGALLOC_GFP)' on arm64.
> > >
> > > Or we could put the pgd_cache initialisation in pgtable_cache_init, which
> > > sounds like the right place for it anyway.
> > >
> >
> > Indeed.
>
> Patch below. Seems to do the job on my Juno.
>
> Will
>
> --->8
>
> From 39b5be9b4233a9f212b98242bddf008f379b5122 Mon Sep 17 00:00:00 2001
> From: Will Deacon <[email-masked]>
> Date: Tue, 5 Jan 2016 15:36:59 +0000
> Subject: [PATCH] arm64: mm: move pgd_cache initialisation to
>  pgtable_cache_init
>
> Initialising the suppport for EFI runtime services requires us to
> allocate a pgd off the back of an early_initcall. On systems where the
> PGD_SIZE is smaller than PAGE_SIZE (e.g. 64k pages and 48-bit VA), the
> pgd_cache isn't initialised at this stage, and we panic with a NULL
> dereference during boot:
>
>   Unable to handle kernel NULL pointer dereference at virtual address 00000000
>
>   __create_mapping.isra.5+0x84/0x350
>   create_pgd_mapping+0x20/0x28
>   efi_create_mapping+0x5c/0x6c
>   arm_enable_runtime_services+0x154/0x1e4
>   do_one_initcall+0x8c/0x190
>   kernel_init_freeable+0x84/0x1ec
>   kernel_init+0x10/0xe0
>   ret_from_fork+0x10/0x50
>
> This patch fixes the problem by initialising the pgd_cache earlier, in
> the pgtable_cache_init callback, which sounds suspiciously like what it
> was intended for.
>
> Reported-by: Dennis Chen <[email-masked]>
> Signed-off-by: Will Deacon <[email-masked]>
> ---
>  arch/arm64/include/asm/pgtable.h |  3 ++-
>  arch/arm64/mm/pgd.c              | 12 ++++++------
>  2 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 35a318c2fd87..a87e964d2791 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -676,7 +676,8 @@ extern int kern_addr_valid(unsigned long addr);
>
>  #include <asm-generic/pgtable.h>
>
> -#define pgtable_cache_init() do { } while (0)
> +void pgd_cache_init(void);
> +#define pgtable_cache_init   pgd_cache_init
>
>  /*
>   * On AArch64, the cache coherency is handled via the set_pte_at() function.
> diff --git a/arch/arm64/mm/pgd.c b/arch/arm64/mm/pgd.c
> index cb3ba1b812e7..ae11d4e03d0e 100644
> --- a/arch/arm64/mm/pgd.c
> +++ b/arch/arm64/mm/pgd.c
> @@ -46,14 +46,14 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
>               kmem_cache_free(pgd_cache, pgd);
>  }
>
> -static int __init pgd_cache_init(void)
> +void __init pgd_cache_init(void)
>  {
> +     if (PGD_SIZE == PAGE_SIZE)
> +             return;
> +
It doesn't need to add a new if statement here.
>       /*
>        * Naturally aligned pgds required by the architecture.
>        */
> -     if (PGD_SIZE != PAGE_SIZE)
> -             pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_SIZE,
> -                                           SLAB_PANIC, NULL);
The deleted code here is more better, seems we don't need to change it here
> -     return 0;
Nice.
> +     pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_SIZE,
> +                                   SLAB_PANIC, NULL);

>  }
> -core_initcall(pgd_cache_init);
The new patch is reasonable for me.

> --
> 2.1.4
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