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SubjectRe: [PATCH v8 7/9] KVM: arm/arm64: context-switch ptrauth registers
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Hi Kristina,

On 4/5/19 12:59 AM, Kristina Martsenko wrote:
> On 02/04/2019 03:27, Amit Daniel Kachhap wrote:
>> From: Mark Rutland <mark.rutland@arm.com>
>>
>> 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.
>
> [...]
>
>> diff --git a/arch/arm64/include/asm/kvm_ptrauth_asm.h b/arch/arm64/include/asm/kvm_ptrauth_asm.h
>> new file mode 100644
>> index 0000000..65f99e9
>> --- /dev/null
>> +++ b/arch/arm64/include/asm/kvm_ptrauth_asm.h
>> @@ -0,0 +1,106 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +/* arch/arm64/include/asm/kvm_ptrauth_asm.h: Guest/host ptrauth save/restore
>> + * Copyright 2019 Arm Limited
>> + * Author: Mark Rutland <mark.rutland@arm.com>
>> + * Amit Daniel Kachhap <amit.kachhap@arm.com>
>> + */
>> +
>> +#ifndef __ASM_KVM_PTRAUTH_ASM_H
>> +#define __ASM_KVM_PTRAUTH_ASM_H
>> +
>> +#ifndef __ASSEMBLY__
>> +
>> +#define __ptrauth_save_key(regs, key) \
>> +({ \
>> + regs[key ## KEYLO_EL1] = read_sysreg_s(SYS_ ## key ## KEYLO_EL1); \
>> + regs[key ## KEYHI_EL1] = read_sysreg_s(SYS_ ## key ## KEYHI_EL1); \
>> +})
>> +
>> +#define __ptrauth_save_state(ctxt) \
>> +({ \
>> + __ptrauth_save_key(ctxt->sys_regs, APIA); \
>> + __ptrauth_save_key(ctxt->sys_regs, APIB); \
>> + __ptrauth_save_key(ctxt->sys_regs, APDA); \
>> + __ptrauth_save_key(ctxt->sys_regs, APDB); \
>> + __ptrauth_save_key(ctxt->sys_regs, APGA); \
>> +})
>> +
>> +#else /* __ASSEMBLY__ */
>> +
>> +#include <asm/sysreg.h>
>> +
>> +#ifdef CONFIG_ARM64_PTR_AUTH
>> +
>> +#define PTRAUTH_REG_OFFSET(x) (x - CPU_APIAKEYLO_EL1)
>> +
>> +/*
>> + * CPU_AP*_EL1 values exceed immediate offset range (512) for stp instruction
>> + * so below macros takes CPU_APIAKEYLO_EL1 as base and calculates the offset of
>> + * the keys from this base to avoid an extra add instruction. These macros
>> + * assumes the keys offsets are aligned in a specific increasing order.
>> + */
>> +.macro ptrauth_save_state base, reg1, reg2
>> + mrs_s \reg1, SYS_APIAKEYLO_EL1
>> + mrs_s \reg2, SYS_APIAKEYHI_EL1
>> + stp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APIAKEYLO_EL1)]
>> + mrs_s \reg1, SYS_APIBKEYLO_EL1
>> + mrs_s \reg2, SYS_APIBKEYHI_EL1
>> + stp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APIBKEYLO_EL1)]
>> + mrs_s \reg1, SYS_APDAKEYLO_EL1
>> + mrs_s \reg2, SYS_APDAKEYHI_EL1
>> + stp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APDAKEYLO_EL1)]
>> + mrs_s \reg1, SYS_APDBKEYLO_EL1
>> + mrs_s \reg2, SYS_APDBKEYHI_EL1
>> + stp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APDBKEYLO_EL1)]
>> + mrs_s \reg1, SYS_APGAKEYLO_EL1
>> + mrs_s \reg2, SYS_APGAKEYHI_EL1
>> + stp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APGAKEYLO_EL1)]
>> +.endm
>> +
>> +.macro ptrauth_restore_state base, reg1, reg2
>> + ldp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APIAKEYLO_EL1)]
>> + msr_s SYS_APIAKEYLO_EL1, \reg1
>> + msr_s SYS_APIAKEYHI_EL1, \reg2
>> + ldp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APIBKEYLO_EL1)]
>> + msr_s SYS_APIBKEYLO_EL1, \reg1
>> + msr_s SYS_APIBKEYHI_EL1, \reg2
>> + ldp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APDAKEYLO_EL1)]
>> + msr_s SYS_APDAKEYLO_EL1, \reg1
>> + msr_s SYS_APDAKEYHI_EL1, \reg2
>> + ldp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APDBKEYLO_EL1)]
>> + msr_s SYS_APDBKEYLO_EL1, \reg1
>> + msr_s SYS_APDBKEYHI_EL1, \reg2
>> + ldp \reg1, \reg2, [\base, #PTRAUTH_REG_OFFSET(CPU_APGAKEYLO_EL1)]
>> + msr_s SYS_APGAKEYLO_EL1, \reg1
>> + msr_s SYS_APGAKEYHI_EL1, \reg2
>> +.endm
>> +
>> +.macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3
>> + ldr \reg1, [\g_ctxt, #CPU_HCR_EL2]
>> + and \reg1, \reg1, #(HCR_API | HCR_APK)
>> + cbz \reg1, 1f
>> + add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
>> + ptrauth_restore_state \reg1, \reg2, \reg3
>> +1:
>
> Nit: the label in assembly macros is usually a larger number (see
> assembler.h or alternative.h for example). I think this is to avoid
> future accidents like
>
> cbz x0, 1f
> ptrauth_switch_to_guest x1, x2, x3, x4
> add x5, x5, x6
> 1:
> ...
>
> where the code would incorrectly branch to the label inside
> ptrauth_switch_to_guest, instead of the one after it.
Yes agree that these kind of labels are problematic. I will update in
the next iteration.

Thanks,
Amit Daniel
>
> Thanks,
> Kristina
>
>> +.endm
>> +
>> +.macro ptrauth_switch_to_host g_ctxt, h_ctxt, reg1, reg2, reg3
>> + ldr \reg1, [\g_ctxt, #CPU_HCR_EL2]
>> + and \reg1, \reg1, #(HCR_API | HCR_APK)
>> + cbz \reg1, 2f
>> + add \reg1, \g_ctxt, #CPU_APIAKEYLO_EL1
>> + ptrauth_save_state \reg1, \reg2, \reg3
>> + add \reg1, \h_ctxt, #CPU_APIAKEYLO_EL1
>> + ptrauth_restore_state \reg1, \reg2, \reg3
>> + isb
>> +2:
>> +.endm
>> +
>> +#else /* !CONFIG_ARM64_PTR_AUTH */
>> +.macro ptrauth_switch_to_guest g_ctxt, reg1, reg2, reg3
>> +.endm
>> +.macro ptrauth_switch_to_host g_ctxt, h_ctxt, reg1, reg2, reg3
>> +.endm
>> +#endif /* CONFIG_ARM64_PTR_AUTH */
>> +#endif /* __ASSEMBLY__ */
>> +#endif /* __ASM_KVM_PTRAUTH_ASM_H */
>
>> diff --git a/arch/arm64/kvm/hyp/entry.S b/arch/arm64/kvm/hyp/entry.S
>> index 675fdc1..3a70213 100644
>> --- a/arch/arm64/kvm/hyp/entry.S
>> +++ b/arch/arm64/kvm/hyp/entry.S
>> @@ -24,6 +24,7 @@
>> #include <asm/kvm_arm.h>
>> #include <asm/kvm_asm.h>
>> #include <asm/kvm_mmu.h>
>> +#include <asm/kvm_ptrauth_asm.h>
>>
>> #define CPU_GP_REG_OFFSET(x) (CPU_GP_REGS + x)
>> #define CPU_XREG_OFFSET(x) CPU_GP_REG_OFFSET(CPU_USER_PT_REGS + 8*x)
>> @@ -64,6 +65,9 @@ ENTRY(__guest_enter)
>>
>> add x18, x0, #VCPU_CONTEXT
>>
>> + // Macro ptrauth_switch_to_guest(guest cxt, tmp1, tmp2, tmp3).
>> + ptrauth_switch_to_guest x18, x0, x1, x2
>> +
>> // Restore guest regs x0-x17
>> ldp x0, x1, [x18, #CPU_XREG_OFFSET(0)]
>> ldp x2, x3, [x18, #CPU_XREG_OFFSET(2)]
>> @@ -118,6 +122,9 @@ ENTRY(__guest_exit)
>>
>> get_host_ctxt x2, x3
>>
>> + // Macro ptrauth_switch_to_host(guest cxt, host cxt, tmp1, tmp2, tmp3).
>> + ptrauth_switch_to_host x1, x2, x3, x4, x5
>> +
>> // Now restore the host regs
>> restore_callee_saved_regs x2
>>

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