Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Thu, 21 Sep 2017 16:41:29 -0400
From: Rik van Riel <>
To: Eric Biggers <>,
Cc:,, Andy
 Lutomirski <>, Dave Hansen <>,
 Dmitry Vyukov <>, Fenghua Yu <>, Ingo
 Molnar <>, Kevin Hao <>, Oleg Nesterov
 <>, Wanpeng Li <>, Yu-cheng Yu
 <>, Michael Halcrow <>, Eric
 Biggers <>
Subject: Re: [PATCH v3 3/3] x86/fpu: reinitialize FPU
 registers if restoring FPU state fails

On Thu, 2017-09-21 at 11:52 -0700, Eric Biggers wrote:
> From: Eric Biggers <>
> Userspace can change the FPU state of a task using the ptrace() or
> rt_sigreturn() system calls.  Because reserved bits in the FPU state
> can
> cause the XRSTOR instruction to fail, the kernel has to carefully
> validate that no reserved bits or other invalid values are being set.
> Unfortunately, there have been bugs in this validation code.  For
> example, we were not checking that the 'xcomp_bv' field in the
> xstate_header was 0.  As-is, such bugs are exploitable to read the
> registers of other processes on the system.  To do so, an attacker
> can
> create a task, assign to it an invalid FPU state, then spin in a loop
> and monitor the values of the FPU registers.  Because the task's FPU
> registers are not being restored, sometimes the FPU registers will
> have
> the values from another process.

Reviewed-by: Rik van Riel <>

All rights reversed
Download attachment "signature.asc" of type "application/pgp-signature" (474 bytes)

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.