linux-kernel - Re: [PATCH] x86/asm: add __user on copy_user_handle

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Date:   Thu, 28 Mar 2019 08:24:21 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Ben Dooks <ben.dooks@...ethink.co.uk>
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.co,
        hpa@...or.com, x86@...nel.org, linux-kernel@...ts.codethink.co.uk,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] x86/asm: add __user on copy_user_handle_tail() pointers

On Thu, Feb 28, 2019 at 06:50:27PM +0000, Ben Dooks wrote:
> The copy_user_handle_tail() clearly uses both from and to as pointers
> to user-space memory. This triggers sparse warning on using the calls
> to get and put to user-space. This can be fixed easily by changing the
> call to take __user annotated pointer.s

Well, but copy_user_generic() (which ends up calling the
copy_user_handle_tail() eventually) casts those __user pointers to
(__force void *). Converting them back to __user looks strange to me.

Linus?

Leaving in the rest for reference.

> arch/x86/lib/usercopy_64.c:68:21: warning: incorrect type in argument 1 (different address spaces)
> arch/x86/lib/usercopy_64.c:68:21:    expected void const volatile [noderef] <asn:1>*<noident>
> arch/x86/lib/usercopy_64.c:68:21:    got char *
> arch/x86/lib/usercopy_64.c:70:21: warning: incorrect type in argument 1 (different address spaces)
> arch/x86/lib/usercopy_64.c:70:21:    expected void const volatile [noderef] <asn:1>*<noident>
> arch/x86/lib/usercopy_64.c:70:21:    got char *to
> 
> Signed-off-by: Ben Dooks <ben.dooks@...ethink.co.uk>
> ---
>  arch/x86/include/asm/uaccess_64.h | 2 +-
>  arch/x86/lib/usercopy_64.c        | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/uaccess_64.h b/arch/x86/include/asm/uaccess_64.h
> index a9d637bc301d..cbca2cb28939 100644
> --- a/arch/x86/include/asm/uaccess_64.h
> +++ b/arch/x86/include/asm/uaccess_64.h
> @@ -208,7 +208,7 @@ __copy_from_user_flushcache(void *dst, const void __user *src, unsigned size)
>  }
>  
>  unsigned long
> -copy_user_handle_tail(char *to, char *from, unsigned len);
> +copy_user_handle_tail(char __user *to, char __user *from, unsigned len);
>  
>  unsigned long
>  mcsafe_handle_tail(char *to, char *from, unsigned len);
> diff --git a/arch/x86/lib/usercopy_64.c b/arch/x86/lib/usercopy_64.c
> index ee42bb0cbeb3..aa180424e77a 100644
> --- a/arch/x86/lib/usercopy_64.c
> +++ b/arch/x86/lib/usercopy_64.c
> @@ -60,7 +60,7 @@ EXPORT_SYMBOL(clear_user);
>   * it is not necessary to optimize tail handling.
>   */
>  __visible unsigned long
> -copy_user_handle_tail(char *to, char *from, unsigned len)
> +copy_user_handle_tail(char __user *to, char __user *from, unsigned len)
>  {
>  	for (; len; --len, to++) {
>  		char c;
> -- 
> 2.20.1
> 

-- 
Regards/Gruss,
    Boris.

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