Re: [PATCH v4.9.y 10/42] arm64: futex: Mask __user pointers prior to dereference

[Greg KH <greg@kroah.com>]

On Thu, Apr 12, 2018 at 12:11:06PM +0100, Mark Rutland wrote:
> From: Will Deacon <will.deacon@arm.com>
> 
> commit 91b2d3442f6a44dce875670d702af22737ad5eff upstream.
> 
> The arm64 futex code has some explicit dereferencing of user pointers
> where performing atomic operations in response to a futex command. This
> patch uses masking to limit any speculative futex operations to within
> the user address space.
> 
> Signed-off-by: Will Deacon <will.deacon@arm.com>
> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Mark Rutland <mark.rutland@arm.com> [v4.9 backport]
> Tested-by: Greg Hackmann <ghackmann@google.com>
> ---
>  arch/arm64/include/asm/futex.h | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/futex.h b/arch/arm64/include/asm/futex.h
> index f2585cdd32c2..1d123dd01ee0 100644
> --- a/arch/arm64/include/asm/futex.h
> +++ b/arch/arm64/include/asm/futex.h
> @@ -51,13 +51,14 @@
>  	: "memory")
>  
>  static inline int
> -futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
> +futex_atomic_op_inuser (int encoded_op, u32 __user *_uaddr)
>  {
>  	int op = (encoded_op >> 28) & 7;
>  	int cmp = (encoded_op >> 24) & 15;
>  	int oparg = (encoded_op << 8) >> 20;
>  	int cmparg = (encoded_op << 20) >> 20;
>  	int oldval = 0, ret, tmp;
> +	u32 __user *uaddr = __uaccess_mask_ptr(_uaddr);
>  
>  	if (encoded_op & (FUTEX_OP_OPARG_SHIFT << 28))
>  		oparg = 1 << oparg;
> @@ -109,15 +110,17 @@ futex_atomic_op_inuser (int encoded_op, u32 __user *uaddr)
>  }
>  
>  static inline int
> -futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
> +futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *_uaddr,
>  			      u32 oldval, u32 newval)
>  {
>  	int ret = 0;
>  	u32 val, tmp;
> +	u32 __user *uaddr;
>  
> -	if (!access_ok(VERIFY_WRITE, uaddr, sizeof(u32)))
> +	if (!access_ok(VERIFY_WRITE, _uaddr, sizeof(u32)))
>  		return -EFAULT;
>  
> +	uaddr = __uaccess_mask_ptr(_uaddr);
>  	asm volatile("// futex_atomic_cmpxchg_inatomic\n"
>  ALTERNATIVE("nop", SET_PSTATE_PAN(0), ARM64_HAS_PAN, CONFIG_ARM64_PAN)
>  "	prfm	pstl1strm, %2\n"

This patch doesn't apply at all as it conflicts with commit
d7c5f8c815466fc00785bbff20f25b39643abe01 which was commit 5f16a046f8e1
("arm64: futex: Fix undefined behaviour with FUTEX_OP_OPARG_SHIFT
usage") upstream.

Any chance you can provide a correct backport of this?

thanks,

greg k-h