Re: [PATCH v4 3/5] x86, entry: Switch stacks on a paranoid entry from userspace

Borislav Petkov
2014-11-24T15:55:18Z

On Fri, Nov 21, 2014 at 01:26:09PM -0800, Andy Lutomirski wrote:
> This causes all non-NMI, non-double-fault kernel entries from
> userspace to run on the normal kernel stack. Double-fault is
> exempt to minimize confusion if we double-fault directly from
> userspace due to a bad kernel stack.
>
> This is, suprisingly, simpler and shorter than the current code. It
> removes the IMO rather frightening paranoid_userspace path, and it
> make sync_regs much simpler.
>
> There is no risk of stack overflow due to this change -- the kernel
> stack that we switch to is empty.
>
> This will also enable us to create non-atomic sections within
> machine checks from userspace, which will simplify memory failure
> handling. It will also allow the upcoming fsgsbase code to be
> simplified, because it doesn't need to worry about usergs when
> scheduling in paranoid_exit, as that code no longer exists.
>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Andi Kleen <andi@firstfloor.org>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Signed-off-by: Andy Lutomirski <luto@amacapital.net>

Acked-by: Borislav Petkov <bp@suse.de>

--
Regards/Gruss,
Boris.

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