Re: [RFC UKL 05/10] x86/uaccess: Make access_ok UKL aware

[Andy Lutomirski]

On Mon, Oct 3, 2022, at 3:21 PM, Ali Raza wrote:
> When configured for UKL, access_ok needs to account for the unified address
> space that is used by the kernel and the process being run. To do this,
> they need to check the task struct field added earlier to determine where
> the execution that is making the check is running. For a zero value, the
> normal boundary definitions apply, but non-zero value indicates a UKL
> thread and a shared address space should be assumed.

I think this is just wrong.  Why should a UKL process be able to read() to kernel (high-half) memory?

set_fs() is gone.  Please keep it gone.

>
> Cc: Jonathan Corbet <corbet@xxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Michal Marek <michal.lkml@xxxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxx>
> Cc: Eric Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
> Cc: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
> Cc: Dietmar Eggemann <dietmar.eggemann@xxxxxxx>
> Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> Cc: Ben Segall <bsegall@xxxxxxxxxx>
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Cc: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
> Cc: Valentin Schneider <vschneid@xxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
>
> Signed-off-by: Ali Raza <aliraza@xxxxxx>
> ---
>  arch/x86/include/asm/uaccess.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 913e593a3b45..adef521b2e59 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -37,11 +37,19 @@ static inline bool pagefault_disabled(void);
>   * Return: true (nonzero) if the memory block may be valid, false (zero)
>   * if it is definitely invalid.
>   */
> +#ifdef CONFIG_UNIKERNEL_LINUX
> +#define access_ok(addr, size)					\
> +({									\
> +	WARN_ON_IN_IRQ();						\
> +	(is_ukl_thread() ? 1 : likely(__access_ok(addr, size)));	\
> +})
> +#else
>  #define access_ok(addr, size)					\
>  ({									\
>  	WARN_ON_IN_IRQ();						\
>  	likely(__access_ok(addr, size));				\
>  })
> +#endif
> 
>  #include <asm-generic/access_ok.h>
> 
> -- 
> 2.21.3