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

From: gengdongjiu
Date: Sat Oct 14 2017 - 23:12:27 EST

Next message: Kees Cook: "[PATCH] Makefile: Another fix for stackprotector _AUTO mode"
Previous message: kbuild test robot: "Re: [PATCH v5 03/10] kexec_file: factor out arch_kexec_kernel_*() from x86, powerpc"
In reply to: Marc Zyngier: "Re: [PATCH] arm64: KVM: set right LR register value for 32 bit guest when inject abort"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

Hi Marc,

On 2017/10/13 23:12, Marc Zyngier wrote:
> On 13/10/17 15:29, gengdongjiu wrote:
>> Hi Marc,
>> Thank you very much for your time to review it.
>>
>>> On 12/10/17 17:44, 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
>>>> Multi-pipeline, so the LR value has an offset to
>>>
>>> What does "Multi-pipeline" mean?
>>
>> I mean the ARM's single-cycle instruction 3-stage pipeline operation, as shown below:
>>
>> fetch decode execute
>> fetch decode execute
>> fetch decode execute
>>
>> when CPU finish instructions fetch, PC=PC + 4
>> when CPU finish instructions decode, PC=PC + 8
>> when CPU finish instructions execution, PC=PC+12
>
> Yeah, and that's called pipelined execution. "Multi-pipeline" doesn't
> mean anything. Also, that's an artefact of the original ARM1
> implementation, and not how modern CPUs work anymore.
Ok, thanks for the clarification.

>
>>
>> that is to say, when happen data abort,
>> the PC = fault instruction address + 12, LR_abt = fault instruction address + 8
>>
>> In order to emulate this abort for KVM, LR_abt needs to add an offset 8 when inject data abort.
>>
>>>
>>>> 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).
>>>>
>>>> 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
>>>
>>> Please document where this table is coming from.
>>
>>
>> Thanks for pointing out. Will add it.
>> It come from: DDI0487A_k_armv8_arm_iss10775, "G1.12.3 Overview of exception entry", Table G1-10 Offsets applied to Link value for exceptions taken to non-EL2 modes
>>
>>>
>>>>
>>>> Signed-off-by: Dongjiu Geng <gengdongjiu@xxxxxxxxxx>
>>>> Signed-off-by: Haibin Zhang <zhanghaibin7@xxxxxxxxxx>
>>>>
>>>> ---
>>>> For example, 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/arm64/kvm/inject_fault.c | 18 ++++++++++++------
>>>> 1 file changed, 12 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/arch/arm64/kvm/inject_fault.c
>>>> b/arch/arm64/kvm/inject_fault.c index da6a8cf..da93508 100644
>>>> --- a/arch/arm64/kvm/inject_fault.c
>>>> +++ b/arch/arm64/kvm/inject_fault.c
>>>> @@ -33,12 +33,11 @@
>>>> #define LOWER_EL_AArch64_VECTOR 0x400
>>>> #define LOWER_EL_AArch32_VECTOR 0x600
>>>>
>>>> -static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32
>>>> vect_offset)
>>>> +static void prepare_fault32(struct kvm_vcpu *vcpu, u32 mode, u32 vect_offset,
>>>> + u32 return_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 sctlr = vcpu_cp15(vcpu, c1_SCTLR);
>>>>
>>>> cpsr = mode | COMPAT_PSR_I_BIT;
>>>> @@ -65,7 +64,11 @@ static void prepare_fault32(struct kvm_vcpu *vcpu,
>>>> u32 mode, u32 vect_offset)
>>>>
>>>> static void inject_undef32(struct kvm_vcpu *vcpu) {
>>>> - prepare_fault32(vcpu, COMPAT_PSR_MODE_UND, 4);
>>>> + unsigned long spsr_value = *vcpu_cpsr(vcpu);
>>>> + bool is_thumb = (spsr_value & COMPAT_PSR_T_BIT);
>>>> + u32 return_offset = (is_thumb) ? 2 : 4;
>>>> +
>>>> + prepare_fault32(vcpu, COMPAT_PSR_MODE_UND, 4, return_offset);
>>>> }
>>>>
>>>> /*
>>>> @@ -75,21 +78,24 @@ static void inject_undef32(struct kvm_vcpu *vcpu)
>>>> static void inject_abt32(struct kvm_vcpu *vcpu, bool is_pabt,
>>>> unsigned long addr)
>>>> {
>>>> - u32 vect_offset;
>>>> + u32 vect_offset, return_offset;
>>>> u32 *far, *fsr;
>>>> bool is_lpae;
>>>>
>>>> if (is_pabt) {
>>>> vect_offset = 12;
>>>> + return_offset = 4;
>>>> far = &vcpu_cp15(vcpu, c6_IFAR);
>>>> fsr = &vcpu_cp15(vcpu, c5_IFSR);
>>>> } else { /* !iabt */
>>>> vect_offset = 16;
>>>> + return_offset = 8;
>>>> far = &vcpu_cp15(vcpu, c6_DFAR);
>>>> fsr = &vcpu_cp15(vcpu, c5_DFSR);
>>>> }
>>>>
>>>> - prepare_fault32(vcpu, COMPAT_PSR_MODE_ABT | COMPAT_PSR_A_BIT, vect_offset);
>>>> + prepare_fault32(vcpu, COMPAT_PSR_MODE_ABT | COMPAT_PSR_A_BIT,
>>>> + vect_offset, return_offset);
>>>>
>>>> *far = addr;
>>>>
>>>>
>>>
>>> So instead of adding this extra parameter and littering the code with random constants, why don't you actually implement the table you've
>>> put in the commit log and compute the offset in a single place (which is likely to be prepare_fault32)?
>>
>> Marc,
>> It because multiple abort(Undefined Abort/Prefetch Abort/Data Abort) call the prepare_fault32(), if adding to a single place in prepare_fault32(),prepare_fault32() will
>> not know whether the Abort injection is for Prefetch Abort or Data Abort or Undefined Abort, then will be confused for the value of "return_offset"
>>
>> For example:
>> inject_abt32() is used to inject prefetch Abort or Data Abort, it passes same parameters to call prepare_fault32() for the two Abort. If adding and computing the offset in a prepare_fault32(),
>> it will be confused to compute the offset, because it does not know whether this function call is for prefetch Abort or Data Abort. [1]
>>
>> If computing the offset in a single place, do you have better idea for that?
>
> Yes. Realise that vect_offset uniquely identify the type of fault we're
> trying to inject:
Good suggestion, I will follow that.

>
> diff --git a/arch/arm64/kvm/inject_fault.c b/arch/arm64/kvm/inject_fault.c
> index da6a8cfa54a0..0416f1857c68 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;

Thanks for the example.

>
> Please also update the 32bit code accordingly, as it looks broken too.
yes, I also notice that 32 bit code has the same issue, I will update them too.

>
> Thanks,
>
> M.
>

Next message: Kees Cook: "[PATCH] Makefile: Another fix for stackprotector _AUTO mode"
Previous message: kbuild test robot: "Re: [PATCH v5 03/10] kexec_file: factor out arch_kexec_kernel_*() from x86, powerpc"
In reply to: Marc Zyngier: "Re: [PATCH] arm64: KVM: set right LR register value for 32 bit guest when inject abort"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]