From: Borislav Petkov <bp@alien8.de>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: LKML <linux-kernel@vger.kernel.org>,
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>,
Rik van Riel <riel@surriel.com>
Subject: Re: [patch V3 4/6] x86/pkru: Make PKRU=0 actually work
Date: Tue, 8 Jun 2021 22:06:18 +0200 [thread overview]
Message-ID: <YL/Nuuu8zvKvh3D0@zn.tnic> (raw)
In-Reply-To: <87tum8xj4x.ffs@nanos.tec.linutronix.de>
On Tue, Jun 08, 2021 at 09:15:42PM +0200, Thomas Gleixner wrote:
> But if nothing touched the FPU between T1 scheduling out and back in,
> then the fpregs_state is still valid which means switch_fpu_return()
> does nothing and just clears TIF_NEED_FPU_LOAD. Back to user space with
> DEFAULT_PKRU loaded. -> FAIL #2!
Ah ok.
> Why? It was clearly wrong and I can reproduce it with a hack which
> forces a schedule to a kernel thread and it fails all the way back to
> user space.
Oh, I was speculating about some weird luserspace's behavior of clearing
PKRU and then relying on the buggy behavior of getting PKRU restored to
DEFAULT_PKRU.
I know, it is nuts but it is user-visible change. And yeah, probably
nothing does that...
> I chased that because I observed sporadic failures when forcing PKRU to
> init state and then observed the default key being written. I had some
> extra trace_printks there to analyze something completely different :)
As you do. :-)
--
Regards/Gruss,
Boris.
https://people.kernel.org/tglx/notes-about-netiquette
next prev parent reply other threads:[~2021-06-08 20:06 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-08 14:36 [patch V3 0/6] x86/fpu: Mop up XSAVES and related damage Thomas Gleixner
2021-06-08 14:36 ` [patch V3 1/6] x86/fpu: Prevent state corruption in __fpu__restore_sig() Thomas Gleixner
2021-06-09 14:46 ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2021-06-08 14:36 ` [patch V3 2/6] x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer Thomas Gleixner
2021-06-09 14:46 ` [tip: x86/urgent] " tip-bot2 for Andy Lutomirski
2021-06-08 14:36 ` [patch V3 3/6] x86/process: Check PF_KTHREAD and not current->mm for kernel threads Thomas Gleixner
2021-06-09 14:46 ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
2021-06-10 17:10 ` [patch V3 3/6] " Andy Lutomirski
2021-06-10 20:54 ` Thomas Gleixner
2021-06-11 1:04 ` Andy Lutomirski
2021-06-08 14:36 ` [patch V3 4/6] x86/pkru: Make PKRU=0 actually work Thomas Gleixner
2021-06-08 15:40 ` Borislav Petkov
2021-06-08 19:15 ` Thomas Gleixner
2021-06-08 20:06 ` Borislav Petkov [this message]
2021-06-08 16:06 ` Dave Hansen
2021-06-08 19:06 ` Thomas Gleixner
2021-06-08 21:37 ` Babu Moger
2021-06-09 14:46 ` [tip: x86/urgent] x86/pkru: Write hardware init value to PKRU when xstate is init tip-bot2 for Thomas Gleixner
2021-06-08 14:36 ` [patch V3 5/6] x86/fpu: Add address range checks to copy_user_to_xstate() Thomas Gleixner
2021-06-09 12:56 ` [tip: x86/fpu] " tip-bot2 for Andy Lutomirski
2021-06-08 14:36 ` [patch V3 6/6] selftests/x86: Test signal frame XSTATE header corruption handling Thomas Gleixner
2021-06-09 8:38 ` David Edmondson
2021-06-09 12:56 ` [tip: x86/fpu] " tip-bot2 for Andy Lutomirski
2021-06-08 16:08 ` [patch V3 0/6] x86/fpu: Mop up XSAVES and related damage Dave Hansen
2021-06-08 18:46 ` Rik van Riel
2021-06-09 19:18 ` [PATCH] x86/fpu: Reset state for all signal restore failures Thomas Gleixner
2021-06-10 6:39 ` [tip: x86/urgent] " tip-bot2 for Thomas Gleixner
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