[stable:PATCH v4.9.323] arm64: entry: Restore tramp_map_kernel ISB

[James Morse]

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 at nvidia.com>
Tested-by: Sumit Gupta <sumitg at nvidia.com>
Cc: <stable at vger.kernel.org>
Signed-off-by: James Morse <james.morse at arm.com>
---
This only applies to the v4.9 backport, as v4.14 has the QCOM_FALKOR_E1003
workaround.

 arch/arm64/kernel/entry.S | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 1f79abb1e5dd..4551c0f35fc4 100644
--- 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
-- 
2.30.2