[81/89] KVM: arm64: Inject SIGSEGV on illegal accesses

Message ID	20220519134204.5379-82-will@kernel.org (mailing list archive)
State	New, archived
Headers	show Return-Path: <kvm-owner@kernel.org> From: Will Deacon <will@kernel.org> To: kvmarm@lists.cs.columbia.edu Cc: Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>, Sean Christopherson <seanjc@google.com>, Alexandru Elisei <alexandru.elisei@arm.com>, Andy Lutomirski <luto@amacapital.net>, Catalin Marinas <catalin.marinas@arm.com>, James Morse <james.morse@arm.com>, Chao Peng <chao.p.peng@linux.intel.com>, Quentin Perret <qperret@google.com>, Suzuki K Poulose <suzuki.poulose@arm.com>, Michael Roth <michael.roth@amd.com>, Mark Rutland <mark.rutland@arm.com>, Fuad Tabba <tabba@google.com>, Oliver Upton <oupton@google.com>, Marc Zyngier <maz@kernel.org>, kernel-team@android.com, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH 81/89] KVM: arm64: Inject SIGSEGV on illegal accesses Date: Thu, 19 May 2022 14:41:56 +0100 Message-Id: <20220519134204.5379-82-will@kernel.org> In-Reply-To: <20220519134204.5379-1-will@kernel.org> References: <20220519134204.5379-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk
Series	KVM: arm64: Base support for the pKVM hypervisor at EL2 \| expand [00/89] KVM: arm64: Base support for the pKVM hypervisor at EL2 [01/89] KVM: arm64: Handle all ID registers trapped for a protected VM [02/89] KVM: arm64: Remove redundant hyp_assert_lock_held() assertions [03/89] KVM: arm64: Return error from kvm_arch_init_vm() on allocation failure [04/89] KVM: arm64: Ignore 'kvm-arm.mode=protected' when using VHE [05/89] KVM: arm64: Extend comment in has_vhe() [06/89] KVM: arm64: Drop stale comment [07/89] KVM: arm64: Move hyp refcount manipulation helpers [08/89] KVM: arm64: Back hyp_vmemmap for all of memory [09/89] KVM: arm64: Unify identifiers used to distinguish host and hypervisor [10/89] KVM: arm64: Implement do_donate() helper for donating memory [11/89] KVM: arm64: Prevent the donation of no-map pages [12/89] KVM: arm64: Add helpers to pin memory shared with hyp [13/89] KVM: arm64: Include asm/kvm_mmu.h in nvhe/mem_protect.h [14/89] KVM: arm64: Add hyp_spinlock_t static initializer [15/89] KVM: arm64: Introduce shadow VM state at EL2 [16/89] KVM: arm64: Instantiate VM shadow data from EL1 [17/89] KVM: arm64: Make hyp stage-1 refcnt correct on the whole range [18/89] KVM: arm64: Factor out private range VA allocation [19/89] KVM: arm64: Add pcpu fixmap infrastructure at EL2 [20/89] KVM: arm64: Provide I-cache invalidation by VA at EL2 [21/89] KVM: arm64: Allow non-coallescable pages in a hyp_pool [22/89] KVM: arm64: Add generic hyp_memcache helpers [23/89] KVM: arm64: Instantiate guest stage-2 page-tables at EL2 [24/89] KVM: arm64: Return guest memory from EL2 via dedicated teardown memcache [25/89] KVM: arm64: Add flags to struct hyp_page [26/89] KVM: arm64: Provide a hypercall for the host to reclaim guest memory [27/89] KVM: arm64: Extend memory sharing to allow host-to-guest transitions [28/89] KVM: arm64: Consolidate stage-2 init in one function [29/89] KVM: arm64: Check for PTE validity when checking for executable/cacheable [30/89] KVM: arm64: Do not allow memslot changes after first VM run under pKVM [31/89] KVM: arm64: Disallow dirty logging and RO memslots with pKVM [32/89] KVM: arm64: Use the shadow vCPU structure in handle___kvm_vcpu_run() [33/89] KVM: arm64: Handle guest stage-2 page-tables entirely at EL2 [34/89] KVM: arm64: Don't access kvm_arm_hyp_percpu_base at EL1 [35/89] KVM: arm64: Unmap kvm_arm_hyp_percpu_base from the host [36/89] KVM: arm64: Maintain a copy of 'kvm_arm_vmid_bits' at EL2 [37/89] KVM: arm64: Explicitly map kvm_vgic_global_state at EL2 [38/89] KVM: arm64: Don't map host sections in pkvm [39/89] KVM: arm64: Extend memory donation to allow host-to-guest transitions [40/89] KVM: arm64: Split up nvhe/fixed_config.h [41/89] KVM: arm64: Make vcpu_{read,write}_sys_reg available to HYP code [42/89] KVM: arm64: Simplify vgic-v3 hypercalls [43/89] KVM: arm64: Add the {flush,sync}_vgic_state() primitives [44/89] KVM: arm64: Introduce predicates to check for protected state [45/89] KVM: arm64: Add the {flush,sync}_timer_state() primitives [46/89] KVM: arm64: Introduce the pkvm_vcpu_{load,put} hypercalls [47/89] KVM: arm64: Add current vcpu and shadow_state lookup primitive [48/89] KVM: arm64: Skip __kvm_adjust_pc() for protected vcpus [49/89] KVM: arm64: Add hyp per_cpu variable to track current physical cpu number [50/89] KVM: arm64: Ensure that TLBs and I-cache are private to each vcpu [51/89] KVM: arm64: Introduce per-EC entry/exit handlers [52/89] KVM: arm64: Introduce lazy-ish state sync for non-protected VMs [53/89] KVM: arm64: Lazy host FP save/restore [54/89] KVM: arm64: Reduce host/shadow vcpu state copying [55/89] KVM: arm64: Do not pass the vcpu to __pkvm_host_map_guest() [56/89] KVM: arm64: Check directly whether the vcpu is protected [57/89] KVM: arm64: Trap debug break and watch from guest [58/89] KVM: arm64: Restrict protected VM capabilities [59/89] KVM: arm64: Do not support MTE for protected VMs [60/89] KVM: arm64: Refactor reset_mpidr to extract its computation [61/89] KVM: arm64: Reset sysregs for protected VMs [62/89] KVM: arm64: Move pkvm_vcpu_init_traps to shadow vcpu init [63/89] KVM: arm64: Fix initializing traps in protected mode [64/89] KVM: arm64: Advertise GICv3 sysreg interface to protected guests [65/89] KVM: arm64: Force injection of a data abort on NISV MMIO exit [66/89] KVM: arm64: Donate memory to protected guests [67/89] KVM: arm64: Add EL2 entry/exit handlers for pKVM guests [68/89] KVM: arm64: Move vgic state between host and shadow vcpu structures [69/89] KVM: arm64: Do not update virtual timer state for protected VMs [70/89] KVM: arm64: Refactor kvm_vcpu_enable_ptrauth() for hyp use [71/89] KVM: arm64: Initialize shadow vm state at hyp [72/89] KVM: arm64: Track the SVE state in the shadow vcpu [73/89] KVM: arm64: Add HVC handling for protected guests at EL2 [74/89] KVM: arm64: Move pstate reset values to kvm_arm.h [75/89] KVM: arm64: Move some kvm_psci functions to a shared header [76/89] KVM: arm64: Factor out vcpu_reset code for core registers and PSCI [77/89] KVM: arm64: Handle PSCI for protected VMs in EL2 [78/89] KVM: arm64: Don't expose TLBI hypercalls after de-privilege [79/89] KVM: arm64: Add is_pkvm_initialized() helper [80/89] KVM: arm64: Refactor enter_exception64() [81/89] KVM: arm64: Inject SIGSEGV on illegal accesses [82/89] KVM: arm64: Support TLB invalidation in guest context [83/89] KVM: arm64: Avoid BBM when changing only s/w bits in Stage-2 PTE [84/89] KVM: arm64: Extend memory sharing to allow guest-to-host transitions [85/89] KVM: arm64: Document the KVM/arm64-specific calls in hypercalls.rst [86/89] KVM: arm64: Reformat/beautify PTP hypercall documentation [87/89] KVM: arm64: Expose memory sharing hypercalls to protected guests [88/89] KVM: arm64: Introduce KVM_VM_TYPE_ARM_PROTECTED machine type for PVMs [89/89] Documentation: KVM: Add some documentation for Protected KVM on arm64

Message ID

20220519134204.5379-82-will@kernel.org (mailing list archive)

State

New, archived

Headers

From: Will Deacon <will@kernel.org>
To: kvmarm@lists.cs.columbia.edu
Cc: Will Deacon <will@kernel.org>, Ard Biesheuvel <ardb@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Andy Lutomirski <luto@amacapital.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        James Morse <james.morse@arm.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Quentin Perret <qperret@google.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Michael Roth <michael.roth@amd.com>,
        Mark Rutland <mark.rutland@arm.com>,
        Fuad Tabba <tabba@google.com>,
        Oliver Upton <oupton@google.com>,
        Marc Zyngier <maz@kernel.org>, kernel-team@android.com,
        kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: [PATCH 81/89] KVM: arm64: Inject SIGSEGV on illegal accesses
Date: Thu, 19 May 2022 14:41:56 +0100
Message-Id: <20220519134204.5379-82-will@kernel.org>
In-Reply-To: <20220519134204.5379-1-will@kernel.org>
References: <20220519134204.5379-1-will@kernel.org>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

Series

KVM: arm64: Base support for the pKVM hypervisor at EL2 | expand

Commit Message

Will Deacon May 19, 2022, 1:41 p.m. UTC

From: Quentin Perret <qperret@google.com>

The pKVM hypervisor will currently panic if the host tries to access
memory that it doesn't own (e.g. protected guest memory). Sadly, as
guest memory can still be mapped into the VMM's address space, userspace
can trivially crash the kernel/hypervisor by poking into guest memory.

To prevent this, inject the abort back in the host with S1PTW set in the
ESR, hence allowing the host to differentiate this abort from normal
userspace faults and inject a SIGSEGV cleanly.

Signed-off-by: Quentin Perret <qperret@google.com>
---
 arch/arm64/kvm/hyp/nvhe/mem_protect.c | 50 ++++++++++++++++++++++++++-
 arch/arm64/mm/fault.c                 | 22 ++++++++++++
 2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
index d0544259eb01..8459dc33e460 100644
--- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c
+++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c
@@ -549,6 +549,50 @@  static int host_stage2_idmap(u64 addr)
 	return ret;
 }
 
+static void host_inject_abort(struct kvm_cpu_context *host_ctxt)
+{
+	u64 spsr = read_sysreg_el2(SYS_SPSR);
+	u64 esr = read_sysreg_el2(SYS_ESR);
+	u64 ventry, ec;
+
+	/* Repaint the ESR to report a same-level fault if taken from EL1 */
+	if ((spsr & PSR_MODE_MASK) != PSR_MODE_EL0t) {
+		ec = ESR_ELx_EC(esr);
+		if (ec == ESR_ELx_EC_DABT_LOW)
+			ec = ESR_ELx_EC_DABT_CUR;
+		else if (ec == ESR_ELx_EC_IABT_LOW)
+			ec = ESR_ELx_EC_IABT_CUR;
+		else
+			WARN_ON(1);
+		esr &= ~ESR_ELx_EC_MASK;
+		esr |= ec << ESR_ELx_EC_SHIFT;
+	}
+
+	/*
+	 * Since S1PTW should only ever be set for stage-2 faults, we're pretty
+	 * much guaranteed that it won't be set in ESR_EL1 by the hardware. So,
+	 * let's use that bit to allow the host abort handler to differentiate
+	 * this abort from normal userspace faults.
+	 *
+	 * Note: although S1PTW is RES0 at EL1, it is guaranteed by the
+	 * architecture to be backed by flops, so it should be safe to use.
+	 */
+	esr |= ESR_ELx_S1PTW;
+
+	write_sysreg_el1(esr, SYS_ESR);
+	write_sysreg_el1(spsr, SYS_SPSR);
+	write_sysreg_el1(read_sysreg_el2(SYS_ELR), SYS_ELR);
+	write_sysreg_el1(read_sysreg_el2(SYS_FAR), SYS_FAR);
+
+	ventry = read_sysreg_el1(SYS_VBAR);
+	ventry += get_except64_offset(spsr, PSR_MODE_EL1h, except_type_sync);
+	write_sysreg_el2(ventry, SYS_ELR);
+
+	spsr = get_except64_cpsr(spsr, system_supports_mte(),
+				 read_sysreg_el1(SYS_SCTLR), PSR_MODE_EL1h);
+	write_sysreg_el2(spsr, SYS_SPSR);
+}
+
 void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 {
 	struct kvm_vcpu_fault_info fault;
@@ -560,7 +604,11 @@  void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt)
 
 	addr = (fault.hpfar_el2 & HPFAR_MASK) << 8;
 	ret = host_stage2_idmap(addr);
-	BUG_ON(ret && ret != -EAGAIN);
+
+	if (ret == -EPERM)
+		host_inject_abort(host_ctxt);
+	else
+		BUG_ON(ret && ret != -EAGAIN);
 }
 
 struct pkvm_mem_transition {
diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
index 77341b160aca..2b2c16a2535c 100644
--- a/arch/arm64/mm/fault.c
+++ b/arch/arm64/mm/fault.c
@@ -41,6 +41,7 @@ 
 #include <asm/system_misc.h>
 #include <asm/tlbflush.h>
 #include <asm/traps.h>
+#include <asm/virt.h>
 
 struct fault_info {
 	int	(*fn)(unsigned long far, unsigned int esr,
@@ -257,6 +258,15 @@  static inline bool is_el1_permission_fault(unsigned long addr, unsigned int esr,
 	return false;
 }
 
+static bool is_pkvm_stage2_abort(unsigned int esr)
+{
+	/*
+	 * S1PTW should only ever be set in ESR_EL1 if the pkvm hypervisor
+	 * injected a stage-2 abort -- see host_inject_abort().
+	 */
+	return is_pkvm_initialized() && (esr & ESR_ELx_S1PTW);
+}
+
 static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
 							unsigned int esr,
 							struct pt_regs *regs)
@@ -268,6 +278,9 @@  static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
 	    (esr & ESR_ELx_FSC_TYPE) != ESR_ELx_FSC_FAULT)
 		return false;
 
+	if (is_pkvm_stage2_abort(esr))
+		return false;
+
 	local_irq_save(flags);
 	asm volatile("at s1e1r, %0" :: "r" (addr));
 	isb();
@@ -383,6 +396,8 @@  static void __do_kernel_fault(unsigned long addr, unsigned int esr,
 			msg = "read from unreadable memory";
 	} else if (addr < PAGE_SIZE) {
 		msg = "NULL pointer dereference";
+	} else if (is_pkvm_stage2_abort(esr)) {
+		msg = "access to hypervisor-protected memory";
 	} else {
 		if (kfence_handle_page_fault(addr, esr & ESR_ELx_WNR, regs))
 			return;
@@ -572,6 +587,13 @@  static int __kprobes do_page_fault(unsigned long far, unsigned int esr,
 					 addr, esr, regs);
 	}
 
+	if (is_pkvm_stage2_abort(esr)) {
+		if (!user_mode(regs))
+			goto no_context;
+		arm64_force_sig_fault(SIGSEGV, SEGV_ACCERR, far, "stage-2 fault");
+		return 0;
+	}
+
 	perf_sw_event(PERF_COUNT_SW_PAGE_FAULTS, 1, regs, addr);
 
 	/*

[81/89] KVM: arm64: Inject SIGSEGV on illegal accesses

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