linux-kernel - [PATCH] arm64: kvm: use -fno-jump-tables with clang

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Message-Id: <20180518170202.11458-1-samitolvanen@google.com>
Date:   Fri, 18 May 2018 10:02:02 -0700
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Christoffer Dall <christoffer.dall@....com>,
        Marc Zyngier <marc.zyngier@....com>
Cc:     AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH] arm64: kvm: use -fno-jump-tables with clang

Starting with LLVM r308050, clang generates a jump table with EL1
virtual addresses in __init_stage2_translation, which results in a
kernel panic when booting at EL2:

  Kernel panic - not syncing: HYP panic:
  PS:800003c9 PC:ffff0000089e6fd8 ESR:86000004
  FAR:ffff0000089e6fd8 HPFAR:0000000009825000 PAR:0000000000000000
  VCPU:000804fc20001221

  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc7-dirty #3
  Hardware name: ARM Juno development board (r1) (DT)
  Call trace:
  [<ffff000008088ea4>] dump_backtrace+0x0/0x34c
  [<ffff000008089208>] show_stack+0x18/0x20
  [<ffff0000089c73ec>] dump_stack+0xc4/0xfc
  [<ffff0000080c8e1c>] panic+0x138/0x2b4
  [<ffff0000080c8ce4>] panic+0x0/0x2b4
  SMP: stopping secondary CPUs
  SMP: failed to stop secondary CPUs 0-3,5
  Kernel Offset: disabled
  CPU features: 0x002086
  Memory Limit: none
  ---[ end Kernel panic - not syncing: HYP panic:
  PS:800003c9 PC:ffff0000089e6fd8 ESR:86000004
  FAR:ffff0000089e6fd8 HPFAR:0000000009825000 PAR:0000000000000000
  VCPU:000804fc20001221

This change adds -fno-jump-tables to arm64/hyp to work around the
bug.

Suggested-by: AKASHI Takahiro <takahiro.akashi@...aro.org>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/arm64/kvm/hyp/Makefile | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
index 4313f74753332..745b3255e7832 100644
--- a/arch/arm64/kvm/hyp/Makefile
+++ b/arch/arm64/kvm/hyp/Makefile
@@ -5,6 +5,10 @@
 
 ccflags-y += -fno-stack-protector -DDISABLE_BRANCH_PROFILING
 
+ifeq ($(cc-name),clang)
+ccflags-y += -fno-jump-tables
+endif
+
 KVM=../../../../virt/kvm
 
 obj-$(CONFIG_KVM_ARM_HOST) += $(KVM)/arm/hyp/vgic-v3-sr.o
-- 
2.17.0.441.gb46fe60e1d-goog