Re: [uaccess] 780464aed0: WARNING:at_arch/x86/include/asm/uaccess.h:#strnlen_user/0x

From: Masami Hiramatsu
Date: Tue Mar 05 2019 - 03:22:50 EST


On Tue, 5 Mar 2019 11:36:35 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> On Mon, 4 Mar 2019 10:59:22 -0800
> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> I think the better way to do this is allowing strncpy_from_user()
> if some conditions are match, like
>
> - strncpy_from_user() will be able to copy user memory with set_fs(USER_DS)
> - strncpy_from_user() can copy kernel memory with set_fs(KERNEL_DS)
> - strncpy_from_user() can access unsafe memory in IRQ context if
> pagefault is disabled.
>
> This is almost done, except for CONFIG_DEBUG_ATOMIC_SLEEP=y on x86.
>
> So, what about adding a condition to WARN_ON_IN_IRQ() like below
> instead of introducing user_access_ok() ?
>
> diff --git a/arch/x86/include/asm/uaccess.h b/arch/x86/include/asm/uaccess.h
> index 780f2b42c8ef..ec0f0b74c9ab 100644
> --- a/arch/x86/include/asm/uaccess.h
> +++ b/arch/x86/include/asm/uaccess.h
> @@ -70,7 +70,7 @@ static inline bool __chk_range_not_ok(unsigned long addr, unsigned long size, un
> })
>
> #ifdef CONFIG_DEBUG_ATOMIC_SLEEP
> -# define WARN_ON_IN_IRQ() WARN_ON_ONCE(!in_task())
> +# define WARN_ON_IN_IRQ() WARN_ON_ONCE(pagefault_disabled() && !in_task())

Oops, I meant !pagefault_disabled() && !in_task().

> #else
> # define WARN_ON_IN_IRQ()
> #endif
>
> Of course we have to move pagefault_disabled() macro in somewhere better place.

And I think we don't need it. anyway the macro is referenced via linux/uaccess.h.

Thank you,

--
Masami Hiramatsu <mhiramat@xxxxxxxxxx>