On 21/03/2019 06:08, Amit Daniel Kachhap wrote: > Hi Julien, > > On 3/20/19 5:43 PM, Julien Thierry wrote: >> Hi Amit, >> >> On 19/03/2019 08:30, Amit Daniel Kachhap wrote: >>> From: Mark Rutland <mark.rutland@xxxxxxx> >>> >>> When pointer authentication is supported, a guest may wish to use it. >>> This patch adds the necessary KVM infrastructure for this to work, with >>> a semi-lazy context switch of the pointer auth state. >>> >>> Pointer authentication feature is only enabled when VHE is built >>> in the kernel and present in the CPU implementation so only VHE code >>> paths are modified. >>> >>> When we schedule a vcpu, we disable guest usage of pointer >>> authentication instructions and accesses to the keys. While these are >>> disabled, we avoid context-switching the keys. When we trap the guest >>> trying to use pointer authentication functionality, we change to eagerly >>> context-switching the keys, and enable the feature. The next time the >>> vcpu is scheduled out/in, we start again. However the host key save is >>> optimized and implemented inside ptrauth instruction/register access >>> trap. >>> >>> Pointer authentication consists of address authentication and generic >>> authentication, and CPUs in a system might have varied support for >>> either. Where support for either feature is not uniform, it is hidden >>> from guests via ID register emulation, as a result of the cpufeature >>> framework in the host. >>> >>> Unfortunately, address authentication and generic authentication cannot >>> be trapped separately, as the architecture provides a single EL2 trap >>> covering both. If we wish to expose one without the other, we cannot >>> prevent a (badly-written) guest from intermittently using a feature >>> which is not uniformly supported (when scheduled on a physical CPU which >>> supports the relevant feature). Hence, this patch expects both type of >>> authentication to be present in a cpu. >>> >>> This switch of key is done from guest enter/exit assembly as preperation >>> for the upcoming in-kernel pointer authentication support. Hence, these >>> key switching routines are not implemented in C code as they may cause >>> pointer authentication key signing error in some situations. >>> >>> Signed-off-by: Mark Rutland <mark.rutland@xxxxxxx> >>> [Only VHE, key switch in full assembly, vcpu_has_ptrauth checks >>> , save host key in ptrauth exception trap] >>> Signed-off-by: Amit Daniel Kachhap <amit.kachhap@xxxxxxx> >>> Reviewed-by: Julien Thierry <julien.thierry@xxxxxxx> >>> Cc: Marc Zyngier <marc.zyngier@xxxxxxx> >>> Cc: Christoffer Dall <christoffer.dall@xxxxxxx> >>> Cc: kvmarm@xxxxxxxxxxxxxxxxxxxxx >>> --- >>> arch/arm64/include/asm/kvm_host.h | 17 ++++++ >>> arch/arm64/include/asm/kvm_ptrauth_asm.h | 100 >>> +++++++++++++++++++++++++++++++ >>> arch/arm64/kernel/asm-offsets.c | 6 ++ >>> arch/arm64/kvm/guest.c | 14 +++++ >>> arch/arm64/kvm/handle_exit.c | 24 +++++--- >>> arch/arm64/kvm/hyp/entry.S | 7 +++ >>> arch/arm64/kvm/reset.c | 7 +++ >>> arch/arm64/kvm/sys_regs.c | 46 +++++++++++++- >>> virt/kvm/arm/arm.c | 2 + >>> 9 files changed, 212 insertions(+), 11 deletions(-) >>> create mode 100644 arch/arm64/include/asm/kvm_ptrauth_asm.h >>> > [...] >>> +#ifdef CONFIG_ARM64_PTR_AUTH >>> + >>> +#define PTRAUTH_REG_OFFSET(x) (x - CPU_APIAKEYLO_EL1) >> >> I don't really see the point of this macro. You move the pointers of >> kvm_cpu_contexts to point to where the ptr auth registers are (which is >> in the middle of an array) by adding the offset of APIAKEYLO and then we >> have to recompute all offsets with this macro. >> >> Why not just pass the kvm_cpu_context pointers to >> ptrauth_save/restore_state and use the already defined offsets >> (CPU_AP*_EL1) directly? >> >> I think this would also allow to use one less register for the >> ptrauth_switch_to_* macros. > Actually the values of CPU_AP*_EL1 are exceeding the immediate range > (i.e 512), so this was done to keep the immediate offset within the range. > The other way would have been to calculate the destination register but > these would add one more add instruction everywhere. > I should have mentioned them as comments somewhere. Oh, I see. Yes, it would definitely be worth a comment. Thanks, -- Julien Thierry _______________________________________________ kvmarm mailing list kvmarm@xxxxxxxxxxxxxxxxxxxxx https://lists.cs.columbia.edu/mailman/listinfo/kvmarm
