[PATCH v2 3/9] ARM: vfp: use __copy_to_user() when saving VFP state

[linux@armlinux.org.uk (Russell King - ARM Linux)]

On Thu, Sep 06, 2018 at 05:38:02PM +0100, Julien Thierry wrote:
> Use __copy_to_user() rather than __put_user_error() for individual
> members when saving VFP state.
> This has the benefit of disabling/enabling PAN once per copied struct
> intead of once per write.
> 
> Signed-off-by: Julien Thierry <julien.thierry@arm.com>
> ---
>  arch/arm/include/asm/thread_info.h |  4 ++--
>  arch/arm/kernel/signal.c           | 12 ++++++------
>  arch/arm/vfp/vfpmodule.c           | 20 ++++++++------------
>  3 files changed, 16 insertions(+), 20 deletions(-)
> 
> diff --git a/arch/arm/include/asm/thread_info.h b/arch/arm/include/asm/thread_info.h
> index 9b37b6a..8f55dc5 100644
> --- a/arch/arm/include/asm/thread_info.h
> +++ b/arch/arm/include/asm/thread_info.h
> @@ -121,8 +121,8 @@ static inline struct thread_info *current_thread_info(void)
>  struct user_vfp;
>  struct user_vfp_exc;
>  
> -extern int vfp_preserve_user_clear_hwstate(struct user_vfp __user *,
> -					   struct user_vfp_exc __user *);
> +extern int vfp_preserve_user_clear_hwstate(struct user_vfp *,
> +					   struct user_vfp_exc *);
>  extern int vfp_restore_user_hwstate(struct user_vfp *,
>  				    struct user_vfp_exc *);
>  #endif
> diff --git a/arch/arm/kernel/signal.c b/arch/arm/kernel/signal.c
> index 464393d..baa055d 100644
> --- a/arch/arm/kernel/signal.c
> +++ b/arch/arm/kernel/signal.c
> @@ -137,17 +137,17 @@ static int restore_iwmmxt_context(char __user **auxp)
>  
>  static int preserve_vfp_context(struct vfp_sigframe __user *frame)
>  {
> -	const unsigned long magic = VFP_MAGIC;
> -	const unsigned long size = VFP_STORAGE_SIZE;
> +	struct vfp_sigframe kframe;
>  	int err = 0;
>  
> -	__put_user_error(magic, &frame->magic, err);
> -	__put_user_error(size, &frame->size, err);
> +	kframe.magic = VFP_MAGIC;
> +	kframe.size = VFP_STORAGE_SIZE;
>  
> +	err = vfp_preserve_user_clear_hwstate(&kframe.ufp, &kframe.ufp_exc);
>  	if (err)
> -		return -EFAULT;
> +		return err;
>  
> -	return vfp_preserve_user_clear_hwstate(&frame->ufp, &frame->ufp_exc);
> +	return __copy_to_user(frame, &kframe, sizeof(kframe));

This one needs a memset() to ensure that padding is cleared:

/*
 *  8 byte for magic and size, 264 byte for ufp, 12 bytes for ufp_exc,
 *  4 bytes padding.
 */
#define VFP_STORAGE_SIZE        sizeof(struct vfp_sigframe)

so as this patch stands, it results in a leak one word of kernel data
to userspace.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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