[PATCH 4.9 01/28] arm64: entry: Restore tramp_map_kernel ISB

[Greg Kroah-Hartman]

From: James Morse <james.morse@xxxxxxx>

Summit reports that the BHB backports for v4.9 prevent vulnerable
platforms from booting when CONFIG_RANDOMIZE_BASE is enabled.

This is because the trampoline code takes a translation fault when
accessing the data page, because the TTBR write hasn't been completed
by an ISB before the access is made.

Upstream has a complex erratum workaround for QCOM_FALKOR_E1003 in
this area, which removes the ISB when the workaround has been applied.
v4.9 lacks this workaround, but should still have the ISB.

Restore the barrier.

Fixes: aee10c2dd013 ("arm64: entry: Add macro for reading symbol addresses from the trampoline")
Reported-by: Sumit Gupta <sumitg@xxxxxxxxxx>
Tested-by: Sumit Gupta <sumitg@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: James Morse <james.morse@xxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/kernel/entry.S |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -964,6 +964,7 @@ __ni_sys_trace:
 	b	.
 2:
 	tramp_map_kernel	x30
+	isb
 	tramp_data_read_var	x30, vectors
 	prfm	plil1strm, [x30, #(1b - \vector_start)]
 	msr	vbar_el1, x30