From: Dave Hansen <dave.hansen@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Andy Lutomirski <luto@kernel.org>,
Dave Hansen <dave.hansen@linux.intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
Tony Luck <tony.luck@intel.com>,
Yu-cheng Yu <yu-cheng.yu@intel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Subject: Re: [patch V2 00/14] x86/fpu: Mop up XSAVES and related damage
Date: Mon, 7 Jun 2021 06:36:48 -0700 [thread overview]
Message-ID: <eca0add1-849e-6a1a-8ea6-f6b72650c9c8@intel.com> (raw)
In-Reply-To: <87h7i9zv3r.ffs@nanos.tec.linutronix.de>
On 6/7/21 6:02 AM, Thomas Gleixner wrote:
> On Sun, Jun 06 2021 at 01:47, Thomas Gleixner wrote:
>> P.S: I picked up Dave's PKRU series from
> and while looking deeper at that I found the following existing
> inconsistency vs. PKRU:
>
> On exec() the kernel sets PKRU to the default value which is as
> restrictive as possible.
>
> But on sigrestore PKRU when the init optimization is used PKRU is reset
> to the hardware default (0), which is as permissive as possible:
>
> 1) On XRSTOR from user and the signal handler cleared the PKRU feature
> bit in xsave.header.xfeatures. That's true for the fast and the
> slow path.
>
> 2) For the fx_only case which loads the init_fpstate (with my fixes
> applied that's not longer the case)
>
> So that's inconsistent at best.
>
> As the kernel defines the "init" behaviour of PKRU as non-permissive
> on exec() it should do so consequently in sigrestore as well.
Agreed. The kernel has essentially picked its own init value for PKRU,
separate from the hardware init value. It should be applied consistently.
By the way, are you talking specifically about the _error_ paths where
the kernel is unable to XRSTOR the signal XSAVE buffer for some reason,
and tries to apply either init_fpu or the hardware init state instead?
next prev parent reply other threads:[~2021-06-07 13:36 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-05 23:47 [patch V2 00/14] x86/fpu: Mop up XSAVES and related damage Thomas Gleixner
2021-06-05 23:47 ` [patch V2 01/14] selftests/x86: Test signal frame XSTATE header corruption handling Thomas Gleixner
2021-06-05 23:47 ` [patch V2 02/14] x86/fpu: Prevent state corruption in __fpu__restore_sig() Thomas Gleixner
2021-06-07 8:49 ` Borislav Petkov
2021-06-05 23:47 ` [patch V2 03/14] x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer Thomas Gleixner
2021-06-05 23:47 ` [patch V2 04/14] x86/pkru: Make the fpinit state update work Thomas Gleixner
2021-06-07 15:18 ` Borislav Petkov
2021-06-05 23:47 ` [patch V2 05/14] x86/fpu: Limit xstate copy size in xstateregs_set() Thomas Gleixner
2021-06-05 23:47 ` [patch V2 06/14] x86/fpu: Sanitize xstateregs_set() Thomas Gleixner
2021-06-07 19:39 ` Borislav Petkov
2021-06-05 23:47 ` [patch V2 07/14] x86/fpu: Add address range checks to copy_user_to_xstate() Thomas Gleixner
2021-06-05 23:47 ` [patch V2 08/14] x86/fpu: Move inlines where they belong Thomas Gleixner
2021-06-05 23:47 ` [patch V2 09/14] x86/cpu: Sanitize X86_FEATURE_OSPKE Thomas Gleixner
2021-06-05 23:47 ` [patch V2 10/14] x86/fpu: Rename fpu__clear_all() to fpu_flush_thread() Thomas Gleixner
2021-06-05 23:47 ` [patch V2 11/14] x86/pkru: Provide pkru_get_init_value() Thomas Gleixner
2021-06-05 23:47 ` [patch V2 12/14] x86/fpu: Clean up the fpu__clear() variants Thomas Gleixner
2021-06-05 23:47 ` [patch V2 13/14] x86/fpu: Rename xstate copy functions which are related to UABI Thomas Gleixner
2021-06-05 23:47 ` [patch V2 14/14] x86/fpu: Deduplicate copy_uabi_from_user/kernel_to_xstate() Thomas Gleixner
2021-06-07 13:02 ` [patch V2 00/14] x86/fpu: Mop up XSAVES and related damage Thomas Gleixner
2021-06-07 13:36 ` Dave Hansen [this message]
2021-06-07 14:08 ` Thomas Gleixner
2021-06-07 16:38 ` Dave Hansen
2021-06-07 22:51 ` Thomas Gleixner
2021-06-08 14:47 ` Dave Hansen
2021-06-08 11:17 ` Thomas Gleixner
2021-06-08 12:27 ` Thomas Gleixner
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