linux-kernel - Re: [PATCH v3] usercopy: Check valid lifetime via stack depth

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Date:   Fri, 25 Feb 2022 17:46:57 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>, linux-mm@...ck.org,
        Muhammad Usama Anjum <usama.anjum@...labora.com>,
        David Laight <David.Laight@...lab.com>,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v3] usercopy: Check valid lifetime via stack depth

On Fri, 25 Feb 2022 17:35:49 -0800 Kees Cook <keescook@...omium.org> wrote:

> On Fri, Feb 25, 2022 at 04:01:57PM -0800, Andrew Morton wrote:
> > On Fri, 25 Feb 2022 09:33:45 -0800 Kees Cook <keescook@...omium.org> wrote:
> > 
> > > Under CONFIG_HARDENED_USERCOPY=y, when exact stack frame boundary checking
> > > is not available (i.e. everything except x86 with FRAME_POINTER), check
> > > a stack object as being at least "current depth valid", in the sense
> > > that any object within the stack region but not between start-of-stack
> > > and current_stack_pointer should be considered unavailable (i.e. its
> > > lifetime is from a call no longer present on the stack).
> > > 
> > > Introduce ARCH_HAS_CURRENT_STACK_POINTER to track which architectures
> > > have actually implemented the common global register alias.
> > > 
> > > Additionally report usercopy bounds checking failures with an offset
> > > from current_stack_pointer, which may assist with diagnosing failures.
> > > 
> > > The LKDTM USERCOPY_STACK_FRAME_TO and USERCOPY_STACK_FRAME_FROM tests
> > > (once slightly adjusted in a separate patch) will pass again with
> > > this fixed.
> > 
> > Again, what does this actually do?
> 
> [answers]
>

OK, thanks.  I think a new changelog is warranted?

What's your preferred path for upstreaming this change?