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From: Greg KH <gregkh@linuxfoundation.org>
To: "Schmid, Carsten" <Carsten_Schmid@mentor.com>
Cc: "sashal@kernel.org" <sashal@kernel.org>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>
Subject: Re: [PATCH Backport to stable/linux-4.14.y] make 'user_access_begin()' do 'access_ok()'
Date: Wed, 1 Apr 2020 11:32:35 +0200	[thread overview]
Message-ID: <20200401093235.GB2055942@kroah.com> (raw)
In-Reply-To: <1585733082992.99012@mentor.com>

On Wed, Apr 01, 2020 at 09:24:43AM +0000, Schmid, Carsten wrote:
> >From eb5a13ddc30824c20f1e2b662d2c821ad3808526 Mon Sep 17 00:00:00 2001
> From: Linus Torvalds <torvalds@linux-foundation.org>
> Date: Fri, 4 Jan 2019 12:56:09 -0800
> Subject: [PATCH] make 'user_access_begin()' do 'access_ok()'
> 
> [ Upstream commit 594cc251fdd0d231d342d88b2fdff4bc42fb0690 ]
> 
> Fixes CVE-2018-20669
> Backported from v5.0-rc1
> Patch 1/1

Also, that cve was "supposed" to already be fixed in the 4.19.13 kernel
release for some reason, and it's a drm issue, not a core access_ok()
issue.

So why is this needed for 4.14?

> 
> Originally, the rule used to be that you'd have to do access_ok()
> separately, and then user_access_begin() before actually doing the
> direct (optimized) user access.
> 
> But experience has shown that people then decide not to do access_ok()
> at all, and instead rely on it being implied by other operations or
> similar.  Which makes it very hard to verify that the access has
> actually been range-checked.
> 
> If you use the unsafe direct user accesses, hardware features (either
> SMAP - Supervisor Mode Access Protection - on x86, or PAN - Privileged
> Access Never - on ARM) do force you to use user_access_begin().  But
> nothing really forces the range check.
> 
> By putting the range check into user_access_begin(), we actually force
> people to do the right thing (tm), and the range check vill be visible
> near the actual accesses.  We have way too long a history of people
> trying to avoid them.
> 
> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

No s-o-by from you?

> ---
> Rationale:
> When working on stability and security for a project with 4.14 kernel,
> i backported patches from upstream.
> Want to give this work back to the community, as 4.14 is a SLTS.

What is "SLTS"?

thanks,

greg k-h

  parent reply	other threads:[~2020-04-01  9:32 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-01  8:49 [PATCH Backport to stable/linux-4.14.y] make 'user_access_begin()' do 'access_ok()' Schmid, Carsten
2020-04-01  9:24 ` Schmid, Carsten
2020-04-01  9:29   ` Greg KH
2020-04-01  9:32   ` Greg KH [this message]
     [not found]     ` <1585735684794.48644@mentor.com>
2020-04-01 10:32       ` AW: " Schmid, Carsten
2020-04-01 11:01         ` Greg KH

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