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@kernel.org>
Suggested-by: Marc Zyngier <maz@kernel.org>
Suggested-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Will Deacon <will@kernel.org>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210305202124.3768527-1-samitolvanen@google.com

diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
index 0c66a1d408fd71ae199aaa1a509d90689f91b0b2..e831d3dfd50d7cee211d915a7e39f9468ceff154 100644 (file)
--- 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