Commit 7209c868 authored Oct 18, 2016 by James Morse Committed by Will Deacon Oct 20, 2016

arm64: mm: Set PSTATE.PAN from the cpu_enable_pan() call



Commit 338d4f49 ("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>

parent 2a6dcb2b

arch/arm64/mm/fault.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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>
		@@ -672,7 +674,14 @@ 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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