[PATCH 1/6] syscalls: use uaccess_kernel in addr_limit_user_check

[Guenter Roeck]

On Sat, Jul 18, 2020 at 11:48:46AM +0200, Christoph Hellwig wrote:
> On Fri, Jul 17, 2020 at 06:38:50PM -0700, Guenter Roeck wrote:
> > Hi,
> > 
> > On Tue, Jul 14, 2020 at 12:55:00PM +0200, Christoph Hellwig wrote:
> > > Use the uaccess_kernel helper instead of duplicating it.
> > > 
> > > Signed-off-by: Christoph Hellwig <hch at lst.de>
> > 
> > This patch causes a severe hiccup with my mps2-an385 boot test.
> 

I had another look into the code. Right after this patch, I see

#define uaccess_kernel() segment_eq(get_fs(), KERNEL_DS)

Yet, this patch is:

-       if (CHECK_DATA_CORRUPTION(!segment_eq(get_fs(), USER_DS),
+       if (CHECK_DATA_CORRUPTION(uaccess_kernel(),

So there is a negation in the condition. Indeed, the following change
on top of next-20200720 fixes the problem for mps2-an385.

-       if (CHECK_DATA_CORRUPTION(uaccess_kernel(),
+       if (CHECK_DATA_CORRUPTION(!uaccess_kernel(),

How does this work anywhere ?

Thanks,
Guenter

> I guess that is a nommu config?
> 
> Can you try this patch?
> 
> diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h
> index b19c9bec1f7a63..cc7daf374a6eb6 100644
> --- a/arch/arm/include/asm/uaccess.h
> +++ b/arch/arm/include/asm/uaccess.h
> @@ -263,7 +263,7 @@ extern int __put_user_8(void *, unsigned long long);
>   */
>  #define USER_DS			KERNEL_DS
>  
> -#define uaccess_kernel()	(true)
> +#define uaccess_kernel()	(false)
>  #define __addr_ok(addr)		((void)(addr), 1)
>  #define __range_ok(addr, size)	((void)(addr), 0)
>  #define get_fs()		(KERNEL_DS)