[PATCH 0/2] x86/cfi: Fix FineIBT
From: Peter Zijlstra
Date: Thu Jun 15 2023 - 15:40:58 EST
Hi!
Alyssa reported a FineIBT issue; these patches sort that.
Basically the morale of the story is that CALL_NOSPEC and JMP_NOSPEC are
suspect and likely not what you want. The remaining users are:
arch/x86/crypto/crc32c-pcl-intel-asm_64.S: JMP_NOSPEC bufp
This is broken on anything IBT afaict.
arch/x86/include/asm/mshyperv.h: CALL_NOSPEC
arch/x86/include/asm/mshyperv.h: __asm__ __volatile__(CALL_NOSPEC
arch/x86/include/asm/mshyperv.h: __asm__ __volatile__(CALL_NOSPEC
arch/x86/include/asm/mshyperv.h: __asm__ __volatile__ (CALL_NOSPEC
arch/x86/include/asm/mshyperv.h: CALL_NOSPEC
arch/x86/include/asm/mshyperv.h: __asm__ __volatile__ (CALL_NOSPEC
arch/x86/include/asm/xen/hypercall.h: asm volatile(CALL_NOSPEC
These are hypercalls and supposedly the targets are having ENDBR on.
arch/x86/kernel/ftrace_64.S: CALL_NOSPEC r8
The thing is !DYNAMIC_FTRACE only, which we can fix with a Kconfig
dependency I suppose.
arch/x86/kvm/emulate.c: asm("push %[flags]; popf; " CALL_NOSPEC
arch/x86/kvm/emulate.c: asm("push %[flags]; popf; " CALL_NOSPEC " ; pushf; pop %[flags]\n"
calls into the magic fastop stuff and should be ok, those have explicit
ENDBR + IBT_NOSEAL() annotations.
arch/x86/kvm/vmx/vmenter.S: VMX_DO_EVENT_IRQOFF CALL_NOSPEC _ASM_ARG1
calls the IDT vectors manually, so should be ok (gross, but not broken
from this pov).
arch/x86/platform/efi/efi_stub_64.S: CALL_NOSPEC rdi
effectively a nocfi call, so should be ok.