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

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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