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From: "tip-bot2 for Andy Lutomirski" <tip-bot2@linutronix.de>
To: linux-tip-commits@vger.kernel.org
Cc: Andy Lutomirski <luto@kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Borislav Petkov <bp@suse.de>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Rik van Riel <riel@surriel.com>,
	stable@vger.kernel.org, x86@kernel.org,
	linux-kernel@vger.kernel.org
Subject: [tip: x86/urgent] x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer
Date: Wed, 09 Jun 2021 14:46:47 -0000	[thread overview]
Message-ID: <162325000806.29796.8910243345894312766.tip-bot2@tip-bot2> (raw)
In-Reply-To: <20210608144345.758116583@linutronix.de>

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     d8778e393afa421f1f117471144f8ce6deb6953a
Gitweb:        https://git.kernel.org/tip/d8778e393afa421f1f117471144f8ce6deb6953a
Author:        Andy Lutomirski <luto@kernel.org>
AuthorDate:    Tue, 08 Jun 2021 16:36:19 +02:00
Committer:     Borislav Petkov <bp@suse.de>
CommitterDate: Wed, 09 Jun 2021 09:49:38 +02:00

x86/fpu: Invalidate FPU state after a failed XRSTOR from a user buffer

Both Intel and AMD consider it to be architecturally valid for XRSTOR to
fail with #PF but nonetheless change the register state.  The actual
conditions under which this might occur are unclear [1], but it seems
plausible that this might be triggered if one sibling thread unmaps a page
and invalidates the shared TLB while another sibling thread is executing
XRSTOR on the page in question.

__fpu__restore_sig() can execute XRSTOR while the hardware registers
are preserved on behalf of a different victim task (using the
fpu_fpregs_owner_ctx mechanism), and, in theory, XRSTOR could fail but
modify the registers.

If this happens, then there is a window in which __fpu__restore_sig()
could schedule out and the victim task could schedule back in without
reloading its own FPU registers. This would result in part of the FPU
state that __fpu__restore_sig() was attempting to load leaking into the
victim task's user-visible state.

Invalidate preserved FPU registers on XRSTOR failure to prevent this
situation from corrupting any state.

[1] Frequent readers of the errata lists might imagine "complex
    microarchitectural conditions".

Fixes: 1d731e731c4c ("x86/fpu: Add a fastpath to __fpu__restore_sig()")
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Rik van Riel <riel@surriel.com>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210608144345.758116583@linutronix.de
---
 arch/x86/kernel/fpu/signal.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/arch/x86/kernel/fpu/signal.c b/arch/x86/kernel/fpu/signal.c
index d5bc96a..4ab9aeb 100644
--- a/arch/x86/kernel/fpu/signal.c
+++ b/arch/x86/kernel/fpu/signal.c
@@ -369,6 +369,25 @@ static int __fpu__restore_sig(void __user *buf, void __user *buf_fx, int size)
 			fpregs_unlock();
 			return 0;
 		}
+
+		/*
+		 * The above did an FPU restore operation, restricted to
+		 * the user portion of the registers, and failed, but the
+		 * microcode might have modified the FPU registers
+		 * nevertheless.
+		 *
+		 * If the FPU registers do not belong to current, then
+		 * invalidate the FPU register state otherwise the task might
+		 * preempt current and return to user space with corrupted
+		 * FPU registers.
+		 *
+		 * In case current owns the FPU registers then no further
+		 * action is required. The fixup below will handle it
+		 * correctly.
+		 */
+		if (test_thread_flag(TIF_NEED_FPU_LOAD))
+			__cpu_invalidate_fpregs_state();
+
 		fpregs_unlock();
 	} else {
 		/*

  reply	other threads:[~2021-06-09 14:47 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-bot2 for Andy Lutomirski [this message]
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
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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