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From: Dave Hansen <dave.hansen@intel.com>
To: Thomas Gleixner <tglx@linutronix.de>,
	"Yu, Yu-cheng" <yu-cheng.yu@intel.com>,
	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>
Subject: Re: [patch 0/8] x86/fpu: Mop up XSAVES and related damage
Date: Fri, 4 Jun 2021 10:46:24 -0700	[thread overview]
Message-ID: <6a93334d-d771-666f-7fd0-8d152799fb02@intel.com> (raw)
In-Reply-To: <87h7idzpwh.ffs@nanos.tec.linutronix.de>

On 6/4/21 7:05 AM, Thomas Gleixner wrote:
> But looking at the above, it's not clear to me why that PKRU stuff works
> at all (upstream), but I'll figure it out eventually. I'm quite sure
> that it does work by pure chance not by design.

The upstream flush_thread() code appears correct and even intentionally
so.  Just how we must eagerly load PKRU on a context switch, the
fpu__clear*() code eagerly "clears" PKRU.  It doesn't actually zero it,
of course, but reverts the register and the fpstate back to the
'init_pkru_value':

flush_thread()->fpu__clear_all()->fpu__clear(user_only=false)
	copy_init_fpstate_to_fpregs()
		copy_kernel_to_xregs(init_fpu) // fpstate
		copy_init_pkru_to_fpregs()
			 write_pkru(init_pkru_value_snapshot) // fpregs

Andy said you have a fix for this, but I think the new fpu__clear_all()
is failing to do the eager write_pkru().

  parent reply	other threads:[~2021-06-04 17:46 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-02  9:55 [patch 0/8] x86/fpu: Mop up XSAVES and related damage Thomas Gleixner
2021-06-02  9:55 ` [patch 1/8] selftests/x86: Test signal frame XSTATE header corruption handling Thomas Gleixner
2021-06-02 12:38   ` Borislav Petkov
2021-06-02 14:15     ` Thomas Gleixner
2021-06-03 13:16       ` Shuah Khan
2021-06-02 15:59   ` [patch V2 " Thomas Gleixner
2021-06-02 16:02     ` [patch V2a " Thomas Gleixner
2021-06-02  9:55 ` [patch 2/8] x86/fpu: Prevent state corruption in __fpu__restore_sig() Thomas Gleixner
2021-06-02 13:12   ` Borislav Petkov
2021-06-02 14:46     ` Thomas Gleixner
2021-06-02 15:58   ` [patch V2 " Thomas Gleixner
2021-06-02  9:55 ` [patch 3/8] x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer Thomas Gleixner
2021-06-02 15:06   ` Borislav Petkov
2021-06-03 17:30     ` Andy Lutomirski
2021-06-03 19:28       ` Borislav Petkov
2021-06-02  9:55 ` [patch 4/8] x86/fpu: Limit xstate copy size in xstateregs_set() Thomas Gleixner
2021-06-02 17:44   ` Borislav Petkov
2021-06-02  9:55 ` [patch 5/8] x86/fpu: Sanitize xstateregs_set() Thomas Gleixner
2021-06-02 16:01   ` [patch V2 " Thomas Gleixner
2021-06-03 11:32     ` Borislav Petkov
2021-06-03 17:24   ` [patch " Andy Lutomirski
2021-06-02  9:55 ` [patch 6/8] x86/fpu: Add address range checks to copy_user_to_xstate() Thomas Gleixner
2021-06-02  9:55 ` [patch 7/8] x86/fpu: Clean up the fpu__clear() variants Thomas Gleixner
2021-06-02  9:55 ` [patch 8/8] x86/fpu: Deduplicate copy_xxx_to_xstate() Thomas Gleixner
2021-06-03 16:56   ` Andy Lutomirski
2021-06-02 21:28 ` [patch 0/8] x86/fpu: Mop up XSAVES and related damage Yu, Yu-cheng
2021-06-04 14:05   ` Thomas Gleixner
2021-06-04 16:27     ` Yu, Yu-cheng
2021-06-04 17:46     ` Dave Hansen [this message]
2021-06-04 18:14       ` Thomas Gleixner
2021-06-04 22:04 ` Dave Hansen
2021-06-05 10:18   ` Thomas Gleixner
2021-06-05 11:56     ` Thomas Gleixner

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