From: Andy Lutomirski <luto@amacapital.net>
To: Dave Hansen <dave@sr71.net>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
X86 ML <x86@kernel.org>, Linux API <linux-api@vger.kernel.org>,
linux-arch <linux-arch@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Andrew Morton <akpm@linux-foundation.org>,
Andrew Lutomirski <luto@kernel.org>,
Mel Gorman <mgorman@techsingularity.net>,
Dave Hansen <dave.hansen@linux.intel.com>,
Arnd Bergmann <arnd@arndb.de>
Subject: Re: [PATCH 08/10] x86, pkeys: default to a restrictive init PKRU
Date: Fri, 29 Jul 2016 10:29:58 -0700 [thread overview]
Message-ID: <CALCETrWMg=+YSi7Az+gw9B59OoAEkOd=znpr7+++5=UUg6DThw@mail.gmail.com> (raw)
In-Reply-To: <20160729163021.F3C25D4A@viggo.jf.intel.com>
On Fri, Jul 29, 2016 at 9:30 AM, Dave Hansen <dave@sr71.net> wrote:
>
> From: Dave Hansen <dave.hansen@linux.intel.com>
>
> PKRU is the register that lets you disallow writes or all access
> to a given protection key.
>
> The XSAVE hardware defines an "init state" of 0 for PKRU: its
> most permissive state, allowing access/writes to everything.
> Since we start off all new processes with the init state, we
> start all processes off with the most permissive possible PKRU.
>
> This is unfortunate. If a thread is clone()'d [1] before a
> program has time to set PKRU to a restrictive value, that thread
> will be able to write to all data, no matter what pkey is set on
> it. This weakens any integrity guarantees that we want pkeys to
> provide.
>
> To fix this, we define a very restrictive PKRU to override the
> XSAVE-provided value when we create a new FPU context. We choose
> a value that only allows access to pkey 0, which is as
> restrictive as we can practically make it.
>
> This does not cause any practical problems with applications
> using protection keys because we require them to specify initial
> permissions for each key when it is allocated, which override the
> restrictive default.
>
> In the end, this ensures that threads which do not know how to
> manage their own pkey rights can not do damage to data which is
> pkey-protected.
I think you missed the fpu__clear() caller in kernel/fpu/signal.c.
ISTM it might be more comprehensible to change fpu__clear in general
and then special case things you want to behave differently.
next prev parent reply other threads:[~2016-07-29 17:35 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-07-29 16:30 [PATCH 00/10] [v6] System Calls for Memory Protection Keys Dave Hansen
2016-07-29 16:30 ` [PATCH 01/10] x86, pkeys: add fault handling for PF_PK page fault bit Dave Hansen
2016-09-09 11:10 ` [tip:mm/pkeys] x86/pkeys: Add " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 02/10] mm: implement new pkey_mprotect() system call Dave Hansen
2016-09-09 11:11 ` [tip:mm/pkeys] mm: Implement " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 03/10] x86, pkeys: make mprotect_key() mask off additional vm_flags Dave Hansen
2016-09-09 11:11 ` [tip:mm/pkeys] x86/pkeys: Make " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 04/10] x86, pkeys: allocation/free syscalls Dave Hansen
2016-09-09 11:12 ` [tip:mm/pkeys] x86/pkeys: Allocation/free syscalls tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 05/10] x86: wire up protection keys system calls Dave Hansen
2016-09-09 11:12 ` [tip:mm/pkeys] x86: Wire " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 06/10] generic syscalls: wire up memory protection keys syscalls Dave Hansen
2016-09-09 11:12 ` [tip:mm/pkeys] generic syscalls: Wire " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 07/10] pkeys: add details of system call use to Documentation/ Dave Hansen
2016-09-09 11:13 ` [tip:mm/pkeys] pkeys: Add " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 08/10] x86, pkeys: default to a restrictive init PKRU Dave Hansen
2016-07-29 17:29 ` Andy Lutomirski [this message]
2016-07-29 17:50 ` Dave Hansen
2016-07-29 19:44 ` Andy Lutomirski
2016-08-01 14:42 ` Vlastimil Babka
2016-08-01 14:58 ` Dave Hansen
2016-08-02 8:20 ` Vlastimil Babka
2016-09-09 11:13 ` [tip:mm/pkeys] x86/pkeys: Default " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 09/10] x86, pkeys: allow configuration of init_pkru Dave Hansen
2016-08-02 8:28 ` Vlastimil Babka
2016-08-02 14:37 ` Dave Hansen
2016-09-09 11:14 ` [tip:mm/pkeys] x86/pkeys: Allow " tip-bot for Dave Hansen
2016-07-29 16:30 ` [PATCH 10/10] x86, pkeys: add self-tests Dave Hansen
2016-09-09 11:14 ` [tip:mm/pkeys] x86/pkeys: Add self-tests tip-bot for Dave Hansen
2016-08-08 23:18 [PATCH 00/10] [v6] System Calls for Memory Protection Keys Dave Hansen
2016-08-08 23:18 ` [PATCH 08/10] x86, pkeys: default to a restrictive init PKRU Dave Hansen
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