On Wed, Aug 02, 2023 at 02:41:07PM +0530, Nikunj A Dadhania wrote:
> commit 7f4b5cde2409 ("kvm: Disable objtool frame pointer checking for
> vmenter.S") had added the vmenter.o file to the exception list.
>
> objtool gives the following warnings in the newer kernel builds:
>
> arch/x86/kvm/kvm-amd.o: warning: objtool: __svm_vcpu_run+0x17d: BP used as a scratch register
> arch/x86/kvm/kvm-amd.o: warning: objtool: __svm_sev_es_vcpu_run+0x72: BP used as a scratch register
>
> As kvm-amd.o is a link time object, skipping the kvm-amd.o is not possible
> as per the objtool documentation, better to skip the offending functions.
>
> Functions __svm_vcpu_run() and __svm_sev_es_vcpu_run() saves and restores
> RBP. Below is the snippet:
>
> SYM_FUNC_START(__svm_vcpu_run)
> push %_ASM_BP
> <…>
> pop %_ASM_BP
> RET
>
> Add exceptions to skip both these functions. Remove the
> OBJECT_FILES_NON_STANDARD for vmenter.o
>
> Cc: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> Cc: Randy Dunlap <rdunlap@xxxxxxxxxxxxx>
> Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Cc: Sean Christopherson <seanjc@xxxxxxxxxx>
> Reported-by: Ravi Bangoria <ravi.bangoria@xxxxxxx>
> Signed-off-by: Nikunj A Dadhania <nikunj@xxxxxxx>
> ---
> arch/x86/kvm/Makefile | 4 ----
> arch/x86/kvm/svm/vmenter.S | 2 ++
> 2 files changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
> index 80e3fe184d17..0c5c2f090e93 100644
> --- a/arch/x86/kvm/Makefile
> +++ b/arch/x86/kvm/Makefile
> @@ -3,10 +3,6 @@
> ccflags-y += -I $(srctree)/arch/x86/kvm
> ccflags-$(CONFIG_KVM_WERROR) += -Werror
>
> -ifeq ($(CONFIG_FRAME_POINTER),y)
> -OBJECT_FILES_NON_STANDARD_vmenter.o := y
> -endif
> -
> include $(srctree)/virt/kvm/Makefile.kvm
>
> kvm-y += x86.o emulate.o i8259.o irq.o lapic.o \
> diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
> index 8e8295e774f0..8fd37d661c33 100644
> --- a/arch/x86/kvm/svm/vmenter.S
> +++ b/arch/x86/kvm/svm/vmenter.S
> @@ -289,6 +289,7 @@ SYM_FUNC_START(__svm_vcpu_run)
> _ASM_EXTABLE(7b, 70b)
>
> SYM_FUNC_END(__svm_vcpu_run)
> +STACK_FRAME_NON_STANDARD(__svm_vcpu_run)
>
> /**
> * __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
> @@ -388,3 +389,4 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
> _ASM_EXTABLE(1b, 3b)
>
> SYM_FUNC_END(__svm_sev_es_vcpu_run)
> +STACK_FRAME_NON_STANDARD_FP(__svm_sev_es_vcpu_run)
Urgh... no, no, this is all broken.
By marking them with STACK_FRAME_NON_STANDARD you will get no ORC data
at all, and then you also violate the normal framepointer calling
convention.
This means that if you need to unwind here you're up a creek without no
paddles on.
Objtool complains for a reason, your changelog does not provide a
counter argument for that reason.
Hardware/firmware interfaces that require one to violate basic
calling conventions are horrible crap.
