Re: [REPOST PATCH 2/2] pstore/core: drop cmpxchg based updates

[Kees Cook]

On Thu, Sep 8, 2016 at 4:48 AM, Sebastian Andrzej Siewior
<bigeasy@xxxxxxxxxxxxx> wrote:
> I have here a FPGA behind PCIe which exports SRAM which I use for
> pstore. Now it seems that the FPGA no longer supports cmpxchg based
> updates and writes back 0xffâff and returns the same.  This leads to
> crash during crash rendering pstore useless.
> Since I doubt that there is much benefit from using cmpxchg() here, I am
> dropping this atomic access and use the spinlock based version.
>
> Cc: Anton Vorontsov <anton@xxxxxxxxxx>
> Cc: Colin Cross <ccross@xxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Tony Luck <tony.luck@xxxxxxxxx>
> Cc: Rabin Vincent <rabinv@xxxxxxxx>
> Tested-by: Rabin Vincent <rabinv@xxxxxxxx>
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
> ---
> Also fixes this for ARMv7 as Rabin Vincent pointed out:
>         https://lkml.kernel.org/g/CABXOdTfT7xMfiBvRuUS1hsVs=q5q2wY1x1Z8oCyyJNFckM0g0A@xxxxxxxxxxxxxx

Thanks! I've applied this for -next.

-Kees

>
>  fs/pstore/ram_core.c | 43 ++-----------------------------------------
>  1 file changed, 2 insertions(+), 41 deletions(-)
>
> diff --git a/fs/pstore/ram_core.c b/fs/pstore/ram_core.c
> index 76c3f80efdfa..4bae54bb61cd 100644
> --- a/fs/pstore/ram_core.c
> +++ b/fs/pstore/ram_core.c
> @@ -47,39 +47,6 @@ static inline size_t buffer_start(struct persistent_ram_zone *prz)
>         return atomic_read(&prz->buffer->start);
>  }
>
> -/* increase and wrap the start pointer, returning the old value */
> -static size_t buffer_start_add_atomic(struct persistent_ram_zone *prz, size_t a)
> -{
> -       int old;
> -       int new;
> -
> -       do {
> -               old = atomic_read(&prz->buffer->start);
> -               new = old + a;
> -               while (unlikely(new >= prz->buffer_size))
> -                       new -= prz->buffer_size;
> -       } while (atomic_cmpxchg(&prz->buffer->start, old, new) != old);
> -
> -       return old;
> -}
> -
> -/* increase the size counter until it hits the max size */
> -static void buffer_size_add_atomic(struct persistent_ram_zone *prz, size_t a)
> -{
> -       size_t old;
> -       size_t new;
> -
> -       if (atomic_read(&prz->buffer->size) == prz->buffer_size)
> -               return;
> -
> -       do {
> -               old = atomic_read(&prz->buffer->size);
> -               new = old + a;
> -               if (new > prz->buffer_size)
> -                       new = prz->buffer_size;
> -       } while (atomic_cmpxchg(&prz->buffer->size, old, new) != old);
> -}
> -
>  static DEFINE_RAW_SPINLOCK(buffer_lock);
>
>  /* increase and wrap the start pointer, returning the old value */
> @@ -124,9 +91,6 @@ static void buffer_size_add_locked(struct persistent_ram_zone *prz, size_t a)
>         raw_spin_unlock_irqrestore(&buffer_lock, flags);
>  }
>
> -static size_t (*buffer_start_add)(struct persistent_ram_zone *, size_t) = buffer_start_add_atomic;
> -static void (*buffer_size_add)(struct persistent_ram_zone *, size_t) = buffer_size_add_atomic;
> -
>  static void notrace persistent_ram_encode_rs8(struct persistent_ram_zone *prz,
>         uint8_t *data, size_t len, uint8_t *ecc)
>  {
> @@ -338,9 +302,9 @@ int notrace persistent_ram_write(struct persistent_ram_zone *prz,
>                 c = prz->buffer_size;
>         }
>
> -       buffer_size_add(prz, c);
> +       buffer_size_add_locked(prz, c);
>
> -       start = buffer_start_add(prz, c);
> +       start = buffer_start_add_locked(prz, c);
>
>         rem = prz->buffer_size - start;
>         if (unlikely(rem < c)) {
> @@ -426,9 +390,6 @@ static void *persistent_ram_iomap(phys_addr_t start, size_t size,
>                 return NULL;
>         }
>
> -       buffer_start_add = buffer_start_add_locked;
> -       buffer_size_add = buffer_size_add_locked;
> -
>         if (memtype)
>                 va = ioremap(start, size);
>         else
> --
> 2.9.3
>



-- 
Kees Cook
Nexus Security