Re: [PATCH RESEND v2] arm/arm64: KVM: set right LR register value for 32 bit guest when inject abort

[Christoffer Dall]

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