linux-kernel - [PATCH] KVM: arm64: Don't use cbz/adr with external symbols

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Message-Id: <20210305202124.3768527-1-samitolvanen@google.com>
Date:   Fri,  5 Mar 2021 12:21:24 -0800
From:   Sami Tolvanen <samitolvanen@...gle.com>
To:     Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Ard Biesheuvel <ardb@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org,
        Sami Tolvanen <samitolvanen@...gle.com>
Subject: [PATCH] KVM: arm64: Don't use cbz/adr with external symbols

allmodconfig + CONFIG_LTO_CLANG_THIN=y fails to build due to following
linker errors:

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21CC):
  relocation R_AARCH64_CONDBR19 out of range: 2031220 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

  ld.lld: error: irqbypass.c:(function __guest_enter: .text+0x21E0):
  relocation R_AARCH64_ADR_PREL_LO21 out of range: 2031200 is not in
  [-1048576, 1048575]; references hyp_panic
  >>> defined in vmlinux.o

This is because with LTO, the compiler ends up placing hyp_panic()
more than 1MB away from __guest_enter(). Use an unconditional branch
and adr_l instead to fix the issue.

Link: https://github.com/ClangBuiltLinux/linux/issues/1317
Reported-by: Nathan Chancellor <nathan@...nel.org>
Suggested-by: Marc Zyngier <maz@...nel.org>
Suggested-by: Ard Biesheuvel <ardb@...nel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@...gle.com>
---
 arch/arm64/kvm/hyp/entry.S | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index b0afad7a99c6..c62265951467 100644
--- a/arch/arm64/kvm/hyp/entry.S
+++ b/arch/arm64/kvm/hyp/entry.S
@@ -85,8 +85,10 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
 
 	// If the hyp context is loaded, go straight to hyp_panic
 	get_loaded_vcpu x0, x1
-	cbz	x0, hyp_panic
+	cbnz	x0, 1f
+	b	hyp_panic
 
+1:
 	// The hyp context is saved so make sure it is restored to allow
 	// hyp_panic to run at hyp and, subsequently, panic to run in the host.
 	// This makes use of __guest_exit to avoid duplication but sets the
@@ -94,7 +96,7 @@ SYM_INNER_LABEL(__guest_exit_panic, SYM_L_GLOBAL)
 	// current state is saved to the guest context but it will only be
 	// accurate if the guest had been completely restored.
 	adr_this_cpu x0, kvm_hyp_ctxt, x1
-	adr	x1, hyp_panic
+	adr_l	x1, hyp_panic
 	str	x1, [x0, #CPU_XREG_OFFSET(30)]
 
 	get_vcpu_ptr	x1, x0

base-commit: 280d542f6ffac0e6d65dc267f92191d509b13b64
-- 
2.30.1.766.gb4fecdf3b7-goog