On Tue, Oct 17, 2017 at 10:23:49PM +0800, Dongjiu Geng wrote:
> When a exception is trapped to EL2, hardware uses ELR_ELx to hold
> the current fault instruction address. If KVM wants to inject a
> abort to 32 bit guest, it needs to set the LR register for the
> guest to emulate this abort happened in the guest. Because ARM32
> architecture is pipelined execution, so the LR value has an offset to
> the fault instruction address.
>
> The offsets applied to Link value for exceptions as shown below,
> which should be added for the ARM32 link register(LR).
>
> Table taken from ARMv8 ARM DDI0487B-B, table G1-10:
> Exception Offset, for PE state of:
> A32 T32
> Undefined Instruction +4 +2
> Prefetch Abort +4 +4
> Data Abort +8 +8
> IRQ or FIQ +4 +4
>
> Signed-off-by: Dongjiu Geng <gengdongjiu@xxxxxxxxxx>
> Tested-by: Haibin Zhang <zhanghaibin7@xxxxxxxxxx>
>
> ---
> Have tested in both arm32 and arm64
>
> For example, in the arm64 platform, to the undefined instruction injection:
>
> 1. Guest OS call SMC(Secure Monitor Call) instruction in the address
> 0xc025405c, then Guest traps to hypervisor
>
> c0254050: e59d5028 ldr r5, [sp, #40] ; 0x28
> c0254054: e3a03001 mov r3, #1
> c0254058: e1a01003 mov r1, r3
> c025405c: e1600070 smc 0
> c0254060: e30a0270 movw r0, #41584 ; 0xa270
> c0254064: e34c00bf movt r0, #49343 ; 0xc0bf
>
> 2. KVM injects undefined abort to guest
> 3. We will find the fault PC is 0xc0254058, not 0xc025405c.
>
> [ 12.348072] Internal error: Oops - undefined instruction: 0 [#1] SMP ARM
> [ 12.349786] Modules linked in:
> [ 12.350563] CPU: 1 PID: 71 Comm: cat Not tainted 4.1.0-dirty #25
> [ 12.352061] Hardware name: Generic DT based system
> [ 12.353275] task: d9d08000 ti: d9cfe000 task.ti: d9cfe000
> [ 12.354637] PC is at proc_dointvec+0x20/0x60
> [ 12.355717] LR is at proc_sys_call_handler+0xb0/0xc4
> [ 12.356972] pc : [<c0254058>] lr : [<c035699c>] psr: a0060013
> [ 12.356972] sp : d9cffe90 ip : c0254038 fp : 00000001
> [ 12.359824] r10: d9cfff80 r9 : 00000004 r8 : 00000000
> [ 12.361132] r7 : bec21cb0 r6 : d9cffec4 r5 : d9cfff80 r4 : c0e82de0
> [ 12.362766] r3 : 00000001 r2 : bec21cb0 r1 : 00000001 r0 : c0e82de0
> [ 12.364400] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
> [ 12.366183] Control: 10c5383d Table: 59d3406a DAC: 00000015
> [ 12.367623] Process cat (pid: 71, stack limit = 0xd9cfe220)
>
> 4. After correct the LR register, it will have right value
>
> [ 125.763370] Internal error: Oops - undefined instruction: 0 [#2] SMP ARM
> [ 125.767010] Modules linked in:
> [ 125.768472] CPU: 1 PID: 74 Comm: cat Tainted: G D 4.1.0-dirty #25
> [ 125.771854] Hardware name: Generic DT based system
> [ 125.774053] task: db0bb900 ti: d9d10000 task.ti: d9d10000
> [ 125.776821] PC is at proc_dointvec+0x24/0x60
> [ 125.778919] LR is at proc_sys_call_handler+0xb0/0xc4
> [ 125.781269] pc : [<c025405c>] lr : [<c035699c>] psr: a0060013
> [ 125.781269] sp : d9d11e90 ip : c0254038 fp : 00000001
> [ 125.786581] r10: d9d11f80 r9 : 00000004 r8 : 00000000
> [ 125.789673] r7 : be92ccb0 r6 : d9d11ec4 r5 : d9d11f80 r4 : c0e82de0
> [ 125.792828] r3 : 00000001 r2 : be92ccb0 r1 : 00000001 r0 : c0e82de0
> [ 125.795890] Flags: NzCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user
>
> For other exception injection, such as Data/Prefetch abort, also needs to correct
> ---
> arch/arm/kvm/emulate.c | 4 ++--
> arch/arm64/kvm/inject_fault.c | 16 +++++++++++++++-
> 2 files changed, 17 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/kvm/emulate.c b/arch/arm/kvm/emulate.c
> index 0064b86..2419328 100644
> --- a/arch/arm/kvm/emulate.c
> +++ b/arch/arm/kvm/emulate.c
> @@ -227,7 +227,7 @@ void kvm_inject_undefined(struct kvm_vcpu *vcpu)
> u32 return_offset = (is_thumb) ? 2 : 4;
>
> kvm_update_psr(vcpu, UND_MODE);
> - *vcpu_reg(vcpu, 14) = *vcpu_pc(vcpu) - return_offset;
> + *vcpu_reg(vcpu, 14) = *vcpu_pc(vcpu) + return_offset;
>
> /* Branch to exception vector */
> *vcpu_pc(vcpu) = exc_vector_base(vcpu) + vect_offset;
> @@ -242,7 +242,7 @@ static void inject_abt(struct kvm_vcpu *vcpu, bool is_pabt, unsigned long addr)
> unsigned long cpsr = *vcpu_cpsr(vcpu);
> bool is_thumb = (cpsr & PSR_T_BIT);
> u32 vect_offset;
> - u32 return_offset = (is_thumb) ? 4 : 0;
> + u32 return_offset = (is_pabt) ? 4 : 8;
> bool is_lpae;
>
> kvm_update_psr(vcpu, ABT_MODE);
> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> index da6a8cf..0416f18 100644
> --- a/arch/arm64/kvm/inject_fault.c
> +++ b/arch/arm64/kvm/inject_fault.c
> @@ -33,12 +33,26 @@
> #define LOWER_EL_AArch64_VECTOR 0x400
> #define LOWER_EL_AArch32_VECTOR 0x600
>
> +/*
> + * Table taken from ARMv8 ARM DDI0487B-B, table G1-10.
> + */
> +static u8 return_offsets[8][2] = {
> + [0] = { 0, 0 }, /* Reset, unused */
> + [1] = { 4, 2 }, /* Undefined */
> + [2] = { 0, 0 }, /* SVC, unused */
> + [3] = { 4, 4 }, /* Prefetch abort */
> + [4] = { 8, 8 }, /* Data abort */
> + [5] = { 0, 0 }, /* HVC, unused */
> + [6] = { 4, 4 }, /* IRQ, unused */
> + [7] = { 4, 4 }, /* FIQ, unused */
> +};
> +
> static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset)
> {
> unsigned long cpsr;
> unsigned long new_spsr_value = *vcpu_cpsr(vcpu);
> bool is_thumb = (new_spsr_value & COMPAT_PSR_T_BIT);
> - u32 return_offset = (is_thumb) ? 4 : 0;
> + u32 return_offset = return_offsets[vect_offset >> 2][is_thumb];
> u32 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
>
> cpsr = mode | COMPAT_PSR_I_BIT;
> --
> 2.10.1
>
Applied, thanks.
-Christoffer
