diff options
Diffstat (limited to 'arch/arm64/kvm/pauth.c')
| -rw-r--r-- | arch/arm64/kvm/pauth.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/arch/arm64/kvm/pauth.c b/arch/arm64/kvm/pauth.c new file mode 100644 index 0000000000..d5eb3ae876 --- /dev/null +++ b/arch/arm64/kvm/pauth.c @@ -0,0 +1,206 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * Copyright (C) 2024 - Google LLC + * Author: Marc Zyngier <maz@kernel.org> + * + * Primitive PAuth emulation for ERETAA/ERETAB. + * + * This code assumes that is is run from EL2, and that it is part of + * the emulation of ERETAx for a guest hypervisor. That's a lot of + * baked-in assumptions and shortcuts. + * + * Do no reuse for anything else! + */ + +#include <linux/kvm_host.h> + +#include <asm/gpr-num.h> +#include <asm/kvm_emulate.h> +#include <asm/pointer_auth.h> + +/* PACGA Xd, Xn, Xm */ +#define PACGA(d,n,m) \ + asm volatile(__DEFINE_ASM_GPR_NUMS \ + ".inst 0x9AC03000 |" \ + "(.L__gpr_num_%[Rd] << 0) |" \ + "(.L__gpr_num_%[Rn] << 5) |" \ + "(.L__gpr_num_%[Rm] << 16)\n" \ + : [Rd] "=r" ((d)) \ + : [Rn] "r" ((n)), [Rm] "r" ((m))) + +static u64 compute_pac(struct kvm_vcpu *vcpu, u64 ptr, + struct ptrauth_key ikey) +{ + struct ptrauth_key gkey; + u64 mod, pac = 0; + + preempt_disable(); + + if (!vcpu_get_flag(vcpu, SYSREGS_ON_CPU)) + mod = __vcpu_sys_reg(vcpu, SP_EL2); + else + mod = read_sysreg(sp_el1); + + gkey.lo = read_sysreg_s(SYS_APGAKEYLO_EL1); + gkey.hi = read_sysreg_s(SYS_APGAKEYHI_EL1); + + __ptrauth_key_install_nosync(APGA, ikey); + isb(); + + PACGA(pac, ptr, mod); + isb(); + + __ptrauth_key_install_nosync(APGA, gkey); + + preempt_enable(); + + /* PAC in the top 32bits */ + return pac; +} + +static bool effective_tbi(struct kvm_vcpu *vcpu, bool bit55) +{ + u64 tcr = vcpu_read_sys_reg(vcpu, TCR_EL2); + bool tbi, tbid; + + /* + * Since we are authenticating an instruction address, we have + * to take TBID into account. If E2H==0, ignore VA[55], as + * TCR_EL2 only has a single TBI/TBID. If VA[55] was set in + * this case, this is likely a guest bug... + */ + if (!vcpu_el2_e2h_is_set(vcpu)) { + tbi = tcr & BIT(20); + tbid = tcr & BIT(29); + } else if (bit55) { + tbi = tcr & TCR_TBI1; + tbid = tcr & TCR_TBID1; + } else { + tbi = tcr & TCR_TBI0; + tbid = tcr & TCR_TBID0; + } + + return tbi && !tbid; +} + +static int compute_bottom_pac(struct kvm_vcpu *vcpu, bool bit55) +{ + static const int maxtxsz = 39; // Revisit these two values once + static const int mintxsz = 16; // (if) we support TTST/LVA/LVA2 + u64 tcr = vcpu_read_sys_reg(vcpu, TCR_EL2); + int txsz; + + if (!vcpu_el2_e2h_is_set(vcpu) || !bit55) + txsz = FIELD_GET(TCR_T0SZ_MASK, tcr); + else + txsz = FIELD_GET(TCR_T1SZ_MASK, tcr); + + return 64 - clamp(txsz, mintxsz, maxtxsz); +} + +static u64 compute_pac_mask(struct kvm_vcpu *vcpu, bool bit55) +{ + int bottom_pac; + u64 mask; + + bottom_pac = compute_bottom_pac(vcpu, bit55); + + mask = GENMASK(54, bottom_pac); + if (!effective_tbi(vcpu, bit55)) + mask |= GENMASK(63, 56); + + return mask; +} + +static u64 to_canonical_addr(struct kvm_vcpu *vcpu, u64 ptr, u64 mask) +{ + bool bit55 = !!(ptr & BIT(55)); + + if (bit55) + return ptr | mask; + + return ptr & ~mask; +} + +static u64 corrupt_addr(struct kvm_vcpu *vcpu, u64 ptr) +{ + bool bit55 = !!(ptr & BIT(55)); + u64 mask, error_code; + int shift; + + if (effective_tbi(vcpu, bit55)) { + mask = GENMASK(54, 53); + shift = 53; + } else { + mask = GENMASK(62, 61); + shift = 61; + } + + if (esr_iss_is_eretab(kvm_vcpu_get_esr(vcpu))) + error_code = 2 << shift; + else + error_code = 1 << shift; + + ptr &= ~mask; + ptr |= error_code; + + return ptr; +} + +/* + * Authenticate an ERETAA/ERETAB instruction, returning true if the + * authentication succeeded and false otherwise. In all cases, *elr + * contains the VA to ERET to. Potential exception injection is left + * to the caller. + */ +bool kvm_auth_eretax(struct kvm_vcpu *vcpu, u64 *elr) +{ + u64 sctlr = vcpu_read_sys_reg(vcpu, SCTLR_EL2); + u64 esr = kvm_vcpu_get_esr(vcpu); + u64 ptr, cptr, pac, mask; + struct ptrauth_key ikey; + + *elr = ptr = vcpu_read_sys_reg(vcpu, ELR_EL2); + + /* We assume we're already in the context of an ERETAx */ + if (esr_iss_is_eretab(esr)) { + if (!(sctlr & SCTLR_EL1_EnIB)) + return true; + + ikey.lo = __vcpu_sys_reg(vcpu, APIBKEYLO_EL1); + ikey.hi = __vcpu_sys_reg(vcpu, APIBKEYHI_EL1); + } else { + if (!(sctlr & SCTLR_EL1_EnIA)) + return true; + + ikey.lo = __vcpu_sys_reg(vcpu, APIAKEYLO_EL1); + ikey.hi = __vcpu_sys_reg(vcpu, APIAKEYHI_EL1); + } + + mask = compute_pac_mask(vcpu, !!(ptr & BIT(55))); + cptr = to_canonical_addr(vcpu, ptr, mask); + + pac = compute_pac(vcpu, cptr, ikey); + + /* + * Slightly deviate from the pseudocode: if we have a PAC + * match with the signed pointer, then it must be good. + * Anything after this point is pure error handling. + */ + if ((pac & mask) == (ptr & mask)) { + *elr = cptr; + return true; + } + + /* + * Authentication failed, corrupt the canonical address if + * PAuth2 isn't implemented, or some XORing if it is. + */ + if (!kvm_has_pauth(vcpu->kvm, PAuth2)) + cptr = corrupt_addr(vcpu, cptr); + else + cptr = ptr ^ (pac & mask); + + *elr = cptr; + return false; +} |