| Message ID | cover.1710446682.git.ptosi@google.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | KVM: arm64: Add support for hypervisor kCFI | expand |
Hi Pierre-Clément, On Thu, 14 Mar 2024 20:23:00 +0000, Pierre-Clément Tosi <ptosi@google.com> 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. > > 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 or only partially supported at EL2: in nVHE (or pKVM), > CONFIG_CFI_CLANG gets filtered out at build time, preventing the compiler from > injecting the checks. In VHE (or hVHE), EL2 code gets compiled with the checks Are you sure about hVHE? hVHE is essentially the nVHE object running with a slightly different HCR_EL2 configuration. So if you don't have the checks in the nVHE code, you don't have them for hVHE either. Or am I missing something obvious? Thanks, M.
Hi Marc, On Thu, Mar 14, 2024 at 10:40:47PM +0000, Marc Zyngier wrote: > Hi Pierre-Clément, > > On Thu, 14 Mar 2024 20:23:00 +0000, > Pierre-Clément Tosi <ptosi@google.com> 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. > > > > 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 or only partially supported at EL2: in nVHE (or pKVM), > > CONFIG_CFI_CLANG gets filtered out at build time, preventing the compiler from > > injecting the checks. In VHE (or hVHE), EL2 code gets compiled with the checks > > Are you sure about hVHE? hVHE is essentially the nVHE object running > with a slightly different HCR_EL2 configuration. So if you don't have > the checks in the nVHE code, you don't have them for hVHE either. No, I am not and my assumption that hVHE was running the VHE hyp code was wrong. FYI, these patches were tested in VHE, nVHE, and pKVM (with NVHE_EL2_DEBUG set and unset) but not in hVHE (clearly!). Thanks for pointing this out. > > Or am I missing something obvious? > > Thanks, > > M. > > -- > Without deviation from the norm, progress is not possible.
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 or only partially supported at EL2: in nVHE (or pKVM), CONFIG_CFI_CLANG gets filtered out at build time, preventing the compiler from injecting the checks. In VHE (or hVHE), EL2 code gets compiled with the checks but the handlers in VBAR_EL2 are not aware of kCFI and will produce a generic and not-so-helpful panic message such as [ 36.456088][ T200] Kernel panic - not syncing: HYP panic: [ 36.456088][ T200] PS:204003c9 PC:ffffffc080092310 ESR:f2008228 [ 36.456088][ T200] FAR:0000000081a50000 HPFAR:000000000081a500 PAR:1de7ec7edbadc0de [ 36.456088][ T200] VCPU:00000000e189c7cf To address this, - [01/10] 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. - [02/10] & [03/10] (resp.) fix and improve __pkvm_init_switch_pgd for kCFI - [04/10] to [06/10] prepare nVHE for CONFIG_CFI_CLANG and [09/10] enables it - [10/10] improves kCFI error messages by saving then parsing the CPU context As a result, an informative kCFI panic message is printed by or on behalf of EL2 giving the expected type and target address (possibly resolved to a symbol) for VHE/hVHE, nVHE, and pKVM (iff CONFIG_NVHE_EL2_DEBUG=y). Note that kCFI errors remain fatal at EL2, even when CONFIG_CFI_PERMISSIVE=y. Pierre-Clément Tosi (10): KVM: arm64: Fix clobbered ELR in sync abort KVM: arm64: Fix __pkvm_init_switch_pgd C signature KVM: arm64: Pass pointer to __pkvm_init_switch_pgd KVM: arm64: nVHE: Simplify __guest_exit_panic path KVM: arm64: nVHE: Add EL2 sync exception handler KVM: arm64: nVHE: gen-hyprel: Skip R_AARCH64_ABS32 KVM: arm64: VHE: Mark __hyp_call_panic __noreturn arm64: Move esr_comment() to <asm/esr.h> KVM: arm64: nVHE: Support CONFIG_CFI_CLANG at EL2 KVM: arm64: Improve CONFIG_CFI_CLANG error message 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 | 2 -- arch/arm64/kvm/handle_exit.c | 39 +++++++++++++++++++++- arch/arm64/kvm/hyp/entry.S | 43 ++++++++++++++++++++++--- arch/arm64/kvm/hyp/hyp-entry.S | 4 +-- arch/arm64/kvm/hyp/include/hyp/switch.h | 6 ++-- arch/arm64/kvm/hyp/nvhe/Makefile | 6 ++-- arch/arm64/kvm/hyp/nvhe/gen-hyprel.c | 6 ++++ arch/arm64/kvm/hyp/nvhe/host.S | 19 ++++++----- arch/arm64/kvm/hyp/nvhe/hyp-init.S | 11 ++++--- arch/arm64/kvm/hyp/nvhe/setup.c | 6 ++-- arch/arm64/kvm/hyp/vhe/switch.c | 27 ++++++++++++++-- 15 files changed, 149 insertions(+), 40 deletions(-)