| Message ID | 20240610063244.2828978-1-ptosi@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: arm64: Add support for hypervisor kCFI | expand |
On Mon, 10 Jun 2024 07:32:29 +0100, Pierre-Clément Tosi wrote: > CONFIG_CFI_CLANG ("kernel Control Flow Integrity") makes the compiler inject > runtime type checks before any indirect function call. On AArch64, it generates > a BRK instruction to be executed on type mismatch and encodes the indices of the > registers holding the branch target and expected type in the immediate of the > instruction. As a result, a synchronous exception gets triggered on kCFI failure > and the fault handler can retrieve the immediate (and indices) from ESR_ELx. > > [...] Applied to kvmarm/next, thanks! [1/8] KVM: arm64: Fix clobbered ELR in sync abort/SError https://git.kernel.org/kvmarm/kvmarm/c/a8f0655887cc [2/8] KVM: arm64: Fix __pkvm_init_switch_pgd call ABI https://git.kernel.org/kvmarm/kvmarm/c/ea9d7c83d14e [3/8] KVM: arm64: nVHE: Simplify invalid_host_el2_vect https://git.kernel.org/kvmarm/kvmarm/c/6e3b773ed6bc [4/8] KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32 https://git.kernel.org/kvmarm/kvmarm/c/4ab3f9dd561b [5/8] KVM: arm64: VHE: Mark __hyp_call_panic __noreturn https://git.kernel.org/kvmarm/kvmarm/c/3c6eb6487693 [6/8] arm64: Introduce esr_brk_comment, esr_is_cfi_brk https://git.kernel.org/kvmarm/kvmarm/c/7a928b32f1de [7/8] KVM: arm64: Introduce print_nvhe_hyp_panic helper https://git.kernel.org/kvmarm/kvmarm/c/8f3873a39529 [8/8] KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2 https://git.kernel.org/kvmarm/kvmarm/c/eca4ba5b6dff -- Best, Oliver
CONFIG_CFI_CLANG ("kernel Control Flow Integrity") makes the compiler inject runtime type checks before any indirect function call. On AArch64, it generates a BRK instruction to be executed on type mismatch and encodes the indices of the registers holding the branch target and expected type in the immediate of the instruction. As a result, a synchronous exception gets triggered on kCFI failure and the fault handler can retrieve the immediate (and indices) from ESR_ELx. This feature has been supported at EL1 ("host") since it was introduced by b26e484b8bb3 ("arm64: Add CFI error handling"), where cfi_handler() decodes ESR_EL1, giving informative panic messages such as [ 21.885179] CFI failure at lkdtm_indirect_call+0x2c/0x44 [lkdtm] (target: lkdtm_increment_int+0x0/0x1c [lkdtm]; expected type: 0x7e0c52a) [ 21.886593] Internal error: Oops - CFI: 0 [#1] PREEMPT SMP However, it is not supported at EL2 in nVHE (or pKVM), as CONFIG_CFI_CLANG gets filtered out at build time, preventing the compiler from injecting the checks. To address this, - [1/8] fixes an existing bug where the ELR_EL2 was getting clobbered on synchronous exceptions, causing the wrong "PC" to be reported by nvhe_hyp_panic_handler() or __hyp_call_panic(). This is particularly limiting for kCFI, as it would mask the location of the failed type check. - [2/8] fixes a minor C/asm ABI mismatch which would trigger a kCFI failure - [3/8]-[7/8] prepare nVHE for CONFIG_CFI_CLANG and [8/8] enables it Note that kCFI errors remain fatal at EL2, even when CONFIG_CFI_PERMISSIVE=y. Changes in v5 (addressed Will's comments on v4): - Dropped the patch making the handlers report the kCFI target & expected type - Dropped the hypervisor kCFI test module - Dropped the patch introducing handler for EL2h sync exceptions - Dropped the patch renaming __guest_exit_panic - Made invalid_host_el2_vect branch unconditionally to hyp_panic - Changed SP type in __pkvm_init_switch_pgd signature to unsigned long - Changed which registers __pkvm_init_switch_pgd used for intermediates - Fixed typo in commit message about esr_brk_comment() - Fixed mistake in commit message about context of invalid_host_el2_vect Pierre-Clément Tosi (8): KVM: arm64: Fix clobbered ELR in sync abort/SError KVM: arm64: Fix __pkvm_init_switch_pgd call ABI KVM: arm64: nVHE: Simplify invalid_host_el2_vect KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32 KVM: arm64: VHE: Mark __hyp_call_panic __noreturn arm64: Introduce esr_brk_comment, esr_is_cfi_brk KVM: arm64: Introduce print_nvhe_hyp_panic helper KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2 arch/arm64/include/asm/esr.h | 11 +++++++++ arch/arm64/include/asm/kvm_hyp.h | 4 ++-- arch/arm64/kernel/asm-offsets.c | 1 + arch/arm64/kernel/debug-monitors.c | 4 +--- arch/arm64/kernel/traps.c | 8 +++---- arch/arm64/kvm/handle_exit.c | 24 +++++++++++++++----- arch/arm64/kvm/hyp/entry.S | 8 +++++++ arch/arm64/kvm/hyp/include/hyp/switch.h | 5 +++-- arch/arm64/kvm/hyp/nvhe/Makefile | 6 ++--- arch/arm64/kvm/hyp/nvhe/gen-hyprel.c | 6 +++++ arch/arm64/kvm/hyp/nvhe/host.S | 6 ----- arch/arm64/kvm/hyp/nvhe/hyp-init.S | 30 +++++++++++++++---------- arch/arm64/kvm/hyp/nvhe/setup.c | 4 ++-- arch/arm64/kvm/hyp/vhe/switch.c | 3 +-- 14 files changed, 78 insertions(+), 42 deletions(-)