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@xxxxxxx>
Reported-by: Vladimir Murzin <vladimir.murzin@xxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
[will: fixed typo in comment]
Signed-off-by: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # 4.4.35
---
arch/arm64/mm/fault.c | 9 +++++++++
1 file changed, 9 insertions(+)
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index d4634e6942ca..247bae758e1e 100644
--- 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>
@@ -608,7 +610,14 @@ asmlinkage int __exception do_debug_exception(unsigned long addr,
#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 */
--
2.10.1
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