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[PATCH 4.8 34/35] arm64: mm: Set PSTATE.PAN from the cpu_enable_pan() call

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4.8-stable review patch.  If anyone has any objections, please let me know.

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

From: James Morse <james.morse@arm.com>

commit 7209c868600bd8926e37c10b9aae83124ccc1dd8 upstream.

Commit 338d4f49d6f7 ("arm64: kernel: Add support for Privileged Access
Never") enabled PAN by enabling the 'SPAN' feature-bit in SCTLR_EL1.
This means the PSTATE.PAN bit won't be set until the next return to the
kernel from userspace. On a preemptible kernel we may schedule work that
accesses userspace on a CPU before it has done this.

Now that cpufeature enable() calls are scheduled via stop_machine(), we
can set PSTATE.PAN from the cpu_enable_pan() call.

Add WARN_ON_ONCE(in_interrupt()) to check the PSTATE value we updated
is not immediately discarded.

Reported-by: Tony Thompson <anthony.thompson@arm.com>
Reported-by: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
[will: fixed typo in comment]
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 arch/arm64/mm/fault.c |    9 +++++++++
 1 file changed, 9 insertions(+)

--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -29,7 +29,9 @@
 #include <linux/sched.h>
 #include <linux/highmem.h>
 #include <linux/perf_event.h>
+#include <linux/preempt.h>
 
+#include <asm/bug.h>
 #include <asm/cpufeature.h>
 #include <asm/exception.h>
 #include <asm/debug-monitors.h>
@@ -673,7 +675,14 @@ NOKPROBE_SYMBOL(do_debug_exception);
 #ifdef CONFIG_ARM64_PAN
 int cpu_enable_pan(void *__unused)
 {
+	/*
+	 * We modify PSTATE. This won't work from irq context as the PSTATE
+	 * is discarded once we return from the exception.
+	 */
+	WARN_ON_ONCE(in_interrupt());
+
 	config_sctlr_el1(SCTLR_EL1_SPAN, 0);
+	asm(SET_PSTATE_PAN(1));
 	return 0;
 }
 #endif /* CONFIG_ARM64_PAN */

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[PATCH 4.8 00/35] 4.8.13-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 16/35] PCI: Export pcie_find_root_port Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 11/35] ovl: fix d_real() for stacked fs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 01/35] libata-scsi: Fixup ata_gen_passthru_sense() Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 25/35] drm/radeon: fix check for port PM availability Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 14/35] rcu: Fix soft lockup for rcu_nocb_kthread Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 21/35] drm/i915: drop the struct_mutex when wedged or trying to reset Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 02/35] scsi: hpsa: use bus 3 for legacy HBA devices Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 23/35] drm/radeon: fix power state when port pm is unavailable (v2) Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 26/35] arm64: dts: juno: fix cluster sleep state entry latency on all SoC versions Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:10 +0100
  [PATCH 4.8 07/35] thp: fix corner case of munlock() of PTE-mapped THPs Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 10/35] mm: fix false-positive WARN_ON() in truncate/invalidate for hugetlb Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 29/35] drm/mediatek: fix null pointer dereference Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 08/35] zram: fix unbalanced idr management at hot removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 35/35] arm64: suspend: Reconfigure PSTATE after resume from idle Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 34/35] arm64: mm: Set PSTATE.PAN from the cpu_enable_pan() call Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 04/35] ARC: mm: PAE40: Fix crash at munmap Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 24/35] drm/amdgpu: fix check for port PM availability Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 20/35] drm/i915: Dont touch NULL sg on i915_gem_object_get_pages_gtt() error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 05/35] ARC: Dont use "+l" inline asm constraint Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 12/35] Input: change KEY_DATA from 0x275 to 0x277 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 30/35] perf/x86: Restore TASK_SIZE check on frame pointer Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 28/35] pwm: Fix device reference leak Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 03/35] scsi: libfc: fix seconds_since_last_reset miscalculation Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 32/35] batman-adv: Detect missing primaryif during tp_send as error Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 33/35] arm64: cpufeature: Schedule enable() calls instead of calling them via IPI Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  [PATCH 4.8 09/35] kasan: update kasan_global for gcc 7 Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-07 08:20 +0100
  Re: [PATCH 4.8 00/35] 4.8.13-stable review Guenter Roeck <linux@roeck-us.net> - 2016-12-07 17:10 +0100
    Re: [PATCH 4.8 00/35] 4.8.13-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-08 17:30 +0100
  Re: [PATCH 4.8 00/35] 4.8.13-stable review Shuah Khan <shuah.kh@samsung.com> - 2016-12-07 19:20 +0100
    Re: [PATCH 4.8 00/35] 4.8.13-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-08 17:30 +0100
  Re: [PATCH 4.8 00/35] 4.8.13-stable review Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2016-12-08 17:30 +0100

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