Messages in this thread | | | Subject | Re: [PATCH v5 10/20] RISC-V: KVM: Handle MMIO exits for VCPU | From | Alexander Graf <> | Date | Thu, 22 Aug 2019 15:25:41 +0200 |
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On 22.08.19 14:33, Anup Patel wrote: > On Thu, Aug 22, 2019 at 5:44 PM Alexander Graf <graf@amazon.com> wrote: >> >> On 22.08.19 10:44, Anup Patel wrote: >>> We will get stage2 page faults whenever Guest/VM access SW emulated >>> MMIO device or unmapped Guest RAM. >>> >>> This patch implements MMIO read/write emulation by extracting MMIO >>> details from the trapped load/store instruction and forwarding the >>> MMIO read/write to user-space. The actual MMIO emulation will happen >>> in user-space and KVM kernel module will only take care of register >>> updates before resuming the trapped VCPU. >>> >>> The handling for stage2 page faults for unmapped Guest RAM will be >>> implemeted by a separate patch later. >>> >>> Signed-off-by: Anup Patel <anup.patel@wdc.com> >>> Acked-by: Paolo Bonzini <pbonzini@redhat.com> >>> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com> >>> --- >>> arch/riscv/include/asm/kvm_host.h | 11 + >>> arch/riscv/kvm/mmu.c | 7 + >>> arch/riscv/kvm/vcpu_exit.c | 436 +++++++++++++++++++++++++++++- >>> 3 files changed, 451 insertions(+), 3 deletions(-) >>> >>> diff --git a/arch/riscv/include/asm/kvm_host.h b/arch/riscv/include/asm/kvm_host.h >>> index 18f1097f1d8d..4388bace6d70 100644 >>> --- a/arch/riscv/include/asm/kvm_host.h >>> +++ b/arch/riscv/include/asm/kvm_host.h >>> @@ -53,6 +53,12 @@ struct kvm_arch { >>> phys_addr_t pgd_phys; >>> }; >>> >>> +struct kvm_mmio_decode { >>> + unsigned long insn; >>> + int len; >>> + int shift; >>> +}; >>> + >>> struct kvm_cpu_context { >>> unsigned long zero; >>> unsigned long ra; >>> @@ -141,6 +147,9 @@ struct kvm_vcpu_arch { >>> unsigned long irqs_pending; >>> unsigned long irqs_pending_mask; >>> >>> + /* MMIO instruction details */ >>> + struct kvm_mmio_decode mmio_decode; >>> + >>> /* VCPU power-off state */ >>> bool power_off; >>> >>> @@ -160,6 +169,8 @@ static inline void kvm_arch_vcpu_block_finish(struct kvm_vcpu *vcpu) {} >>> int kvm_riscv_setup_vsip(void); >>> void kvm_riscv_cleanup_vsip(void); >>> >>> +int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long hva, >>> + bool is_write); >>> void kvm_riscv_stage2_flush_cache(struct kvm_vcpu *vcpu); >>> int kvm_riscv_stage2_alloc_pgd(struct kvm *kvm); >>> void kvm_riscv_stage2_free_pgd(struct kvm *kvm); >>> diff --git a/arch/riscv/kvm/mmu.c b/arch/riscv/kvm/mmu.c >>> index 04dd089b86ff..2b965f9aac07 100644 >>> --- a/arch/riscv/kvm/mmu.c >>> +++ b/arch/riscv/kvm/mmu.c >>> @@ -61,6 +61,13 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, >>> return 0; >>> } >>> >>> +int kvm_riscv_stage2_map(struct kvm_vcpu *vcpu, gpa_t gpa, unsigned long hva, >>> + bool is_write) >>> +{ >>> + /* TODO: */ >>> + return 0; >>> +} >>> + >>> void kvm_riscv_stage2_flush_cache(struct kvm_vcpu *vcpu) >>> { >>> /* TODO: */ >>> diff --git a/arch/riscv/kvm/vcpu_exit.c b/arch/riscv/kvm/vcpu_exit.c >>> index e4d7c8f0807a..efc06198c259 100644 >>> --- a/arch/riscv/kvm/vcpu_exit.c >>> +++ b/arch/riscv/kvm/vcpu_exit.c >>> @@ -6,9 +6,371 @@ >>> * Anup Patel <anup.patel@wdc.com> >>> */ >>> >>> +#include <linux/bitops.h> >>> #include <linux/errno.h> >>> #include <linux/err.h> >>> #include <linux/kvm_host.h> >>> +#include <asm/csr.h> >>> + >>> +#define INSN_MATCH_LB 0x3 >>> +#define INSN_MASK_LB 0x707f >>> +#define INSN_MATCH_LH 0x1003 >>> +#define INSN_MASK_LH 0x707f >>> +#define INSN_MATCH_LW 0x2003 >>> +#define INSN_MASK_LW 0x707f >>> +#define INSN_MATCH_LD 0x3003 >>> +#define INSN_MASK_LD 0x707f >>> +#define INSN_MATCH_LBU 0x4003 >>> +#define INSN_MASK_LBU 0x707f >>> +#define INSN_MATCH_LHU 0x5003 >>> +#define INSN_MASK_LHU 0x707f >>> +#define INSN_MATCH_LWU 0x6003 >>> +#define INSN_MASK_LWU 0x707f >>> +#define INSN_MATCH_SB 0x23 >>> +#define INSN_MASK_SB 0x707f >>> +#define INSN_MATCH_SH 0x1023 >>> +#define INSN_MASK_SH 0x707f >>> +#define INSN_MATCH_SW 0x2023 >>> +#define INSN_MASK_SW 0x707f >>> +#define INSN_MATCH_SD 0x3023 >>> +#define INSN_MASK_SD 0x707f >>> + >>> +#define INSN_MATCH_C_LD 0x6000 >>> +#define INSN_MASK_C_LD 0xe003 >>> +#define INSN_MATCH_C_SD 0xe000 >>> +#define INSN_MASK_C_SD 0xe003 >>> +#define INSN_MATCH_C_LW 0x4000 >>> +#define INSN_MASK_C_LW 0xe003 >>> +#define INSN_MATCH_C_SW 0xc000 >>> +#define INSN_MASK_C_SW 0xe003 >>> +#define INSN_MATCH_C_LDSP 0x6002 >>> +#define INSN_MASK_C_LDSP 0xe003 >>> +#define INSN_MATCH_C_SDSP 0xe002 >>> +#define INSN_MASK_C_SDSP 0xe003 >>> +#define INSN_MATCH_C_LWSP 0x4002 >>> +#define INSN_MASK_C_LWSP 0xe003 >>> +#define INSN_MATCH_C_SWSP 0xc002 >>> +#define INSN_MASK_C_SWSP 0xe003 >>> + >>> +#define INSN_LEN(insn) ((((insn) & 0x3) < 0x3) ? 2 : 4) >>> + >>> +#ifdef CONFIG_64BIT >>> +#define LOG_REGBYTES 3 >>> +#else >>> +#define LOG_REGBYTES 2 >>> +#endif >>> +#define REGBYTES (1 << LOG_REGBYTES) >>> + >>> +#define SH_RD 7 >>> +#define SH_RS1 15 >>> +#define SH_RS2 20 >>> +#define SH_RS2C 2 >>> + >>> +#define RV_X(x, s, n) (((x) >> (s)) & ((1 << (n)) - 1)) >>> +#define RVC_LW_IMM(x) ((RV_X(x, 6, 1) << 2) | \ >>> + (RV_X(x, 10, 3) << 3) | \ >>> + (RV_X(x, 5, 1) << 6)) >>> +#define RVC_LD_IMM(x) ((RV_X(x, 10, 3) << 3) | \ >>> + (RV_X(x, 5, 2) << 6)) >>> +#define RVC_LWSP_IMM(x) ((RV_X(x, 4, 3) << 2) | \ >>> + (RV_X(x, 12, 1) << 5) | \ >>> + (RV_X(x, 2, 2) << 6)) >>> +#define RVC_LDSP_IMM(x) ((RV_X(x, 5, 2) << 3) | \ >>> + (RV_X(x, 12, 1) << 5) | \ >>> + (RV_X(x, 2, 3) << 6)) >>> +#define RVC_SWSP_IMM(x) ((RV_X(x, 9, 4) << 2) | \ >>> + (RV_X(x, 7, 2) << 6)) >>> +#define RVC_SDSP_IMM(x) ((RV_X(x, 10, 3) << 3) | \ >>> + (RV_X(x, 7, 3) << 6)) >>> +#define RVC_RS1S(insn) (8 + RV_X(insn, SH_RD, 3)) >>> +#define RVC_RS2S(insn) (8 + RV_X(insn, SH_RS2C, 3)) >>> +#define RVC_RS2(insn) RV_X(insn, SH_RS2C, 5) >>> + >>> +#define SHIFT_RIGHT(x, y) \ >>> + ((y) < 0 ? ((x) << -(y)) : ((x) >> (y))) >>> + >>> +#define REG_MASK \ >>> + ((1 << (5 + LOG_REGBYTES)) - (1 << LOG_REGBYTES)) >>> + >>> +#define REG_OFFSET(insn, pos) \ >>> + (SHIFT_RIGHT((insn), (pos) - LOG_REGBYTES) & REG_MASK) >>> + >>> +#define REG_PTR(insn, pos, regs) \ >>> + (ulong *)((ulong)(regs) + REG_OFFSET(insn, pos)) >>> + >>> +#define GET_RM(insn) (((insn) >> 12) & 7) >>> + >>> +#define GET_RS1(insn, regs) (*REG_PTR(insn, SH_RS1, regs)) >>> +#define GET_RS2(insn, regs) (*REG_PTR(insn, SH_RS2, regs)) >>> +#define GET_RS1S(insn, regs) (*REG_PTR(RVC_RS1S(insn), 0, regs)) >>> +#define GET_RS2S(insn, regs) (*REG_PTR(RVC_RS2S(insn), 0, regs)) >>> +#define GET_RS2C(insn, regs) (*REG_PTR(insn, SH_RS2C, regs)) >>> +#define GET_SP(regs) (*REG_PTR(2, 0, regs)) >>> +#define SET_RD(insn, regs, val) (*REG_PTR(insn, SH_RD, regs) = (val)) >>> +#define IMM_I(insn) ((s32)(insn) >> 20) >>> +#define IMM_S(insn) (((s32)(insn) >> 25 << 5) | \ >>> + (s32)(((insn) >> 7) & 0x1f)) >>> +#define MASK_FUNCT3 0x7000 >>> + >>> +#define STR(x) XSTR(x) >>> +#define XSTR(x) #x >>> + >>> +/* TODO: Handle traps due to unpriv load and redirect it back to VS-mode */ >>> +static ulong get_insn(struct kvm_vcpu *vcpu) >>> +{ >>> + ulong __sepc = vcpu->arch.guest_context.sepc; >>> + ulong __hstatus, __sstatus, __vsstatus; >>> +#ifdef CONFIG_RISCV_ISA_C >>> + ulong rvc_mask = 3, tmp; >>> +#endif >>> + ulong flags, val; >>> + >>> + local_irq_save(flags); >>> + >>> + __vsstatus = csr_read(CSR_VSSTATUS); >>> + __sstatus = csr_read(CSR_SSTATUS); >>> + __hstatus = csr_read(CSR_HSTATUS); >>> + >>> + csr_write(CSR_VSSTATUS, __vsstatus | SR_MXR); >>> + csr_write(CSR_SSTATUS, vcpu->arch.guest_context.sstatus | SR_MXR); >>> + csr_write(CSR_HSTATUS, vcpu->arch.guest_context.hstatus | HSTATUS_SPRV); >> >> What happens when the insn load triggers a page fault, maybe because the >> guest was malicious and did >> >> 1) Run on page 0x1000 >> 2) Remove map for 0x1000, do *not* flush TLB >> 3) Trigger MMIO >> >> That would DOS the host here, as the host kernel would continue running >> in guest address space, right? > > Yes, we can certainly fault while accessing Guest instruction. We will > be fixing this issue in a followup series. We have mentioned this in cover > letter as well.
I don't think the cover letter is the right place for such a comment. Please definitely put it into the code as well, pointing out that this is a known bug. Or even better yet: Fix it up properly :).
In fact, with a bug that dramatic, I'm not even sure we can safely include the code. We're consciously allowing user space to DOS the kernel.
> > BTW, RISC-V spec is going to further improve to provide easy > access of faulting instruction to Hypervisor. > (Refer, https://github.com/riscv/riscv-isa-manual/issues/431)
Yes, we have similar extensions on other archs. Is this going to be an optional addition or a mandatory bit of the hypervisor spec? If it's not mandatory, we can not rely on it, so the current path has to be safe.
Alex
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