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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org,
        Anshuman Khandual <khandual@linux.vnet.ibm.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Sasha Levin <alexander.levin@microsoft.com>
Subject: [PATCH 4.16 062/272] powerpc/fscr: Enable interrupts earlier before calling get_user()
Date:   Mon, 28 May 2018 12:01:35 +0200
Message-Id: <20180528100246.089485193@linuxfoundation.org>
In-Reply-To: <20180528100240.256525891@linuxfoundation.org>
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4.16-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Anshuman Khandual <khandual@linux.vnet.ibm.com>

[ Upstream commit 709b973c844c0b4d115ac3a227a2e5a68722c912 ]

The function get_user() can sleep while trying to fetch instruction
from user address space and causes the following warning from the
scheduler.

BUG: sleeping function called from invalid context

Though interrupts get enabled back but it happens bit later after
get_user() is called. This change moves enabling these interrupts
earlier covering the function get_user(). While at this, lets check
for kernel mode and crash as this interrupt should not have been
triggered from the kernel context.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 arch/powerpc/kernel/traps.c |   32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

--- a/arch/powerpc/kernel/traps.c
+++ b/arch/powerpc/kernel/traps.c
@@ -1612,6 +1612,22 @@ void facility_unavailable_exception(stru
 		value = mfspr(SPRN_FSCR);
 
 	status = value >> 56;
+	if ((hv || status >= 2) &&
+	    (status < ARRAY_SIZE(facility_strings)) &&
+	    facility_strings[status])
+		facility = facility_strings[status];
+
+	/* We should not have taken this interrupt in kernel */
+	if (!user_mode(regs)) {
+		pr_emerg("Facility '%s' unavailable (%d) exception in kernel mode at %lx\n",
+			 facility, status, regs->nip);
+		die("Unexpected facility unavailable exception", regs, SIGABRT);
+	}
+
+	/* We restore the interrupt state now */
+	if (!arch_irq_disabled_regs(regs))
+		local_irq_enable();
+
 	if (status == FSCR_DSCR_LG) {
 		/*
 		 * User is accessing the DSCR register using the problem
@@ -1678,25 +1694,11 @@ void facility_unavailable_exception(stru
 		return;
 	}
 
-	if ((hv || status >= 2) &&
-	    (status < ARRAY_SIZE(facility_strings)) &&
-	    facility_strings[status])
-		facility = facility_strings[status];
-
-	/* We restore the interrupt state now */
-	if (!arch_irq_disabled_regs(regs))
-		local_irq_enable();
-
 	pr_err_ratelimited("%sFacility '%s' unavailable (%d), exception at 0x%lx, MSR=%lx\n",
 		hv ? "Hypervisor " : "", facility, status, regs->nip, regs->msr);
 
 out:
-	if (user_mode(regs)) {
-		_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
-		return;
-	}
-
-	die("Unexpected facility unavailable exception", regs, SIGABRT);
+	_exception(SIGILL, regs, ILL_ILLOPC, regs->nip);
 }
 #endif