From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id CD8D9CCF2F9 for ; Mon, 19 Jan 2026 12:48:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender:List-Subscribe:List-Help :List-Post:List-Archive:List-Unsubscribe:List-Id:Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-ID:Date:Subject:Cc:To:From: Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From: Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=tIV47WBNrHqABt0Xa8UoChkY5SMb1PFtx9Rlto78E0w=; b=ViPP+Roe4DV9aSjFQWbrwthcDJ zoDLWSBXNx0pssB4JueukMr37sDMf59ecDnPjEsnWigD6/gsYonoe6XC+Jt5/OzVik6zvlCw0U+2W KHa7RipQKSSHSgqpoEEQxRK4G8CEWnBRQKI/BEe1FoA1T/hspWXxpcal0Q8OqBa48HaefA5M3fCje ypAdctH7cz+PcxM6iDaLH0n5hvIo+OxxKy0BrAD/gzCcTJ/rk0WcDsB3LX5SpUbQd6Z6KNCIGIhml OJ3Ep06jgh/nUybGfCW7MvIxvz+qlxjKbrEJ1P6X2hXhnqFWD4kOUkMlBWQuQopKVb8ErtTEDNHTg dk3PzPCg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.98.2 #2 (Red Hat Linux)) id 1vhogD-0000000242Z-1oFQ; Mon, 19 Jan 2026 12:48:26 +0000 Received: from sea.source.kernel.org ([172.234.252.31]) by bombadil.infradead.org with esmtps (Exim 4.98.2 #2 (Red Hat Linux)) id 1vhofd-000000023ZF-0kty for linux-arm-kernel@lists.infradead.org; Mon, 19 Jan 2026 12:47:51 +0000 Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id CB320406D3; Mon, 19 Jan 2026 12:47:48 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2894EC19423; Mon, 19 Jan 2026 12:47:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768826868; bh=zDES7PBmjYxKgoDMaGizn1Ikw3zG7pldvral5SPcppg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=sr02XVH2bqzNmLw6OV/5IXNZDqgUZZ9DQZC+hd7HX7of2WdoexKw1/fiHjfLF5ETe a1I62zFdki/Dq7Xc1eZ6H8osQVwgf3QzOECUmddBrqaSwX2r3RQ4Eq9z3SQ1LhUJyW ph8g7AkVmcIC7OM2GguUnvCPM+tTMsbhPSm8+pQ/w9eJRSXvamWmOt9anpuT5p+/f9 FEsJqeTbT0pQBhoB6a2/PoqhIV5maz7pXIkh9SSJxktb5ANAK7L45Jx8Fzoo/mpA7e E4b2E1++23yhkjlKgvvtuBg0AA9018DzRMqXjeUPwvVqfFI0T2Y1r2mengyr1o5Vhn OoxlakWaZ5OtQ== From: Will Deacon To: kvmarm@lists.linux.dev Cc: linux-arm-kernel@lists.infradead.org, Will Deacon , Marc Zyngier , Oliver Upton , Joey Gouly , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Quentin Perret , Fuad Tabba , Vincent Donnefort , Mostafa Saleh Subject: [PATCH v2 18/35] KVM: arm64: Inject SIGSEGV on illegal accesses Date: Mon, 19 Jan 2026 12:46:11 +0000 Message-ID: <20260119124629.2563-19-will@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260119124629.2563-1-will@kernel.org> References: <20260119124629.2563-1-will@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260119_044750_149091_CBE17BB1 X-CRM114-Status: GOOD ( 21.16 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org From: Quentin Perret 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 Signed-off-by: Will Deacon --- arch/arm64/kvm/hyp/nvhe/mem_protect.c | 47 +++++++++++++++++++++++++++ arch/arm64/mm/fault.c | 22 +++++++++++++ 2 files changed, 69 insertions(+) diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c index ef21e8e7a734..41469df46e09 100644 --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c @@ -610,6 +610,50 @@ 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; @@ -633,6 +677,9 @@ void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt) addr = FIELD_GET(HPFAR_EL2_FIPA, fault.hpfar_el2) << 12; switch (host_stage2_idmap(addr)) { + case -EPERM: + host_inject_abort(host_ctxt); + fallthrough; case -EEXIST: case 0: break; diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index be9dab2c7d6a..2294f2061866 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -43,6 +43,7 @@ #include #include #include +#include struct fault_info { int (*fn)(unsigned long far, unsigned long esr, @@ -269,6 +270,15 @@ static inline bool is_el1_permission_fault(unsigned long addr, unsigned long 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 long esr, struct pt_regs *regs) @@ -279,6 +289,9 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr, if (!is_el1_data_abort(esr) || !esr_fsc_is_translation_fault(esr)) return false; + if (is_pkvm_stage2_abort(esr)) + return false; + local_irq_save(flags); asm volatile("at s1e1r, %0" :: "r" (addr)); isb(); @@ -395,6 +408,8 @@ static void __do_kernel_fault(unsigned long addr, unsigned long 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 (esr_fsc_is_translation_fault(esr) && kfence_handle_page_fault(addr, esr & ESR_ELx_WNR, regs)) @@ -621,6 +636,13 @@ static int __kprobes do_page_fault(unsigned long far, unsigned long 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); if (!(mm_flags & FAULT_FLAG_USER)) -- 2.52.0.457.g6b5491de43-goog