Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 11 Mar 2020 14:13:11 +0100
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     Pavel Machek <pavel@denx.de>
Cc:     linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Ard Biesheuvel <ardb@kernel.org>,
        Ingo Molnar <mingo@kernel.org>, linux-efi@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 4.19 84/86] efi/x86: Handle by-ref arguments covering
 multiple pages in mixed mode
Message-ID: <20200311131311.GA3858095@kroah.com>
References: <20200310124530.808338541@linuxfoundation.org>
 <20200310124535.409134291@linuxfoundation.org>
 <20200311130106.GB7285@duo.ucw.cz>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20200311130106.GB7285@duo.ucw.cz>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On Wed, Mar 11, 2020 at 02:01:07PM +0100, Pavel Machek wrote:
> Hi!
> 
> > Currently, the mixed mode runtime service wrappers require that all by-ref
> > arguments that live in the vmalloc space have a size that is a power of 2,
> > and are aligned to that same value. While this is a sensible way to
> > construct an object that is guaranteed not to cross a page boundary, it is
> > overly strict when it comes to checking whether a given object violates
> > this requirement, as we can simply take the physical address of the first
> > and the last byte, and verify that they point into the same physical
> > page.
> 
> Dunno. If start passing buffers that _sometime_ cross page boundaries,
> we'll get hard to debug failures. Maybe original code is better
> buecause it catches problems earlier?
> 
> Furthermore, all existing code should pass aligned, 2^n size buffers,
> so we should not need this in stable?

For some crazy reason you cut out the reason I applied this patch to the
stable tree.  From the changelog text:
	Fixes: f6697df36bdf0bf7 ("x86/efi: Prevent mixed mode boot corruption with CONFIG_VMAP_STACK=y")