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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Yu-cheng Yu <yu-cheng.yu@intel.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
	"H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Tony Luck <tony.luck@intel.com>,
	Andy Lutomirski <luto@kernel.org>, Borislav Petkov <bp@alien8.de>,
	Rik van Riel <riel@surriel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>,
	Fenghua Yu <fenghua.yu@intel.com>,
	Peter Zijlstra <peterz@infradead.org>
Subject: [PATCH] x86/fpu: Deacticate FPU state after failure during state load
Date: Fri, 20 Dec 2019 20:59:06 +0100
Message-ID: <20191220195906.plk6kpmsrikvbcfn@linutronix.de> (raw)
In-Reply-To: <1607597639a6c6255127fef07704ee9193e33166.camel@intel.com>

In __fpu__restore_sig() we need to reset `fpu_fpregs_owner_ctx' if the
FPU state was not fully restored. Otherwise the following may happen
(on the same CPU):

Task A                     Task B               fpu_fpregs_owner_ctx
*active*                                        A.fpu
__fpu__restore_sig()
                           ctx switch           load B.fpu
                           *active*             B.fpu
fpregs_lock()
copy_user_to_fpregs_zeroing()
  copy_kernel_to_xregs() *modify*
  copy_user_to_xregs() *fails*
fpregs_unlock()
                          ctx switch            skip loading B.fpu,
                          *active*              B.fpu

In the succeess case we set `fpu_fpregs_owner_ctx' to the current task.
In the failure case we *might* have modified the FPU state because we
loaded the init state. In this case we need to reset
`fpu_fpregs_owner_ctx' to ensure that the FPU state of the following
task is loaded from saved state (and not skip because it was the
previous state).

Reset `fpu_fpregs_owner_ctx' after a failure during restore occured to
ensure that the FPU state for the next task is always loaded.

Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace")
Reported-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Debugged-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 arch/x86/kernel/fpu/signal.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index 0071b794ed193..400a05e1c1c51 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -352,6 +352,7 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 			fpregs_unlock();
 			return 0;
 		}
+		fpregs_deactivate(fpu);
 		fpregs_unlock();
 	}
 
@@ -403,6 +404,8 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 	}
 	if (!ret)
 		fpregs_mark_activate();
+	else
+		fpregs_deactivate(fpu);
 	fpregs_unlock();
 
 err_out:
-- 
2.24.1


  reply index

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-12 21:08 [PATCH v2 0/3] Fix small issues in XSAVES Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 1/3] x86/fpu/xstate: Fix small issues before adding supervisor xstates Yu-cheng Yu
2019-12-20 20:19   ` Sebastian Andrzej Siewior
2020-01-06 18:15   ` [tip: x86/fpu] x86/fpu/xstate: Fix small issues tip-bot2 for Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 2/3] x86/fpu/xstate: Make xfeature_is_supervisor()/xfeature_is_user() return bool Yu-cheng Yu
2019-12-20 20:19   ` Sebastian Andrzej Siewior
2019-12-20 20:33     ` Yu-cheng Yu
2020-01-06 18:15   ` [tip: x86/fpu] " tip-bot2 for Yu-cheng Yu
2019-12-12 21:08 ` [PATCH v2 3/3] x86/fpu/xstate: Invalidate fpregs when __fpu_restore_sig() fails Yu-cheng Yu
2019-12-18 15:54   ` Sebastian Andrzej Siewior
2019-12-18 20:53     ` Yu-cheng Yu
2019-12-19 14:22       ` Sebastian Andrzej Siewior
2019-12-19 16:44         ` Yu-cheng Yu
2019-12-19 17:16           ` Sebastian Andrzej Siewior
2019-12-19 17:40             ` Yu-cheng Yu
2019-12-20 19:59               ` Sebastian Andrzej Siewior [this message]
2020-01-07 12:52                 ` [tip: x86/fpu] x86/fpu: Deactivate FPU state after failure during state load tip-bot2 for Sebastian Andrzej Siewior
2020-01-07 20:41                   ` Andy Lutomirski
2020-01-07 20:38                     ` Yu-cheng Yu
2020-01-07 21:11                     ` Sebastian Andrzej Siewior
2020-01-08 11:45                       ` Borislav Petkov
2020-01-08 11:46                     ` Borislav Petkov
2019-12-20 20:16               ` [PATCH v2 3/3] x86/fpu/xstate: Invalidate fpregs when __fpu_restore_sig() fails Sebastian Andrzej Siewior
2019-12-20 20:32                 ` Yu-cheng Yu

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