From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BFD153A9611 for ; Thu, 5 Mar 2026 14:45:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772721913; cv=none; b=DTiLCE4pzWNAea1DgkLveHpvaGMocb1BNh2+yy2x6StECwBnTlGqcbTcl1PCf3Bk4pTShMMpBEmBr40FOrCJpDzVzNPPVH1g8N+v07Oa+BmiT9O0QX8ddkFw2iz0gtQpoZ1EMVa3K8nEBlCLeXY8RAY+WaOBtG07ihlJyUjh0+c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772721913; c=relaxed/simple; bh=UkCoLH1y0Fdpy6NDuesWGah04WOm1Qx14uAjVSe9gyo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=hTBuXHTe/LE9IrwsWkzdgS0hj0Gt+Xk6iw9aqIclC6uu7rVVtEKTkljFW2T+V8GlNHgBl6M7+eeEx/IZ0eGy0c7La5JwXDAXMMcsqQpNtVZ5N1aLdNFm25HCJIGdEq4zGfxpcSBaTFOtkGI2y0UiZC7amMVUiwpZEc1PupRZNrY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pqBiaYh5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pqBiaYh5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7D595C2BC9E; Thu, 5 Mar 2026 14:45:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772721913; bh=UkCoLH1y0Fdpy6NDuesWGah04WOm1Qx14uAjVSe9gyo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pqBiaYh5VU8eYBlwYb4haKMMGCfdOryKJHqX2dg5znI/WP/odcSYGSxUQ4Waux71Q oABcuMQjFSbg/wDsPcaOzenOdBsa1SxOpSjO2GF19OE3vAlhxTHCX6GFpYJjhGpoQ0 0vNPHdOqWtv4hMTiw3NbPn0XfSFApwbZbKLs5dH3lhRVUZgB2c/TqT1h1cfH/ADNBo LEu5mCH8ENqXCIchCVjO2+VSVCU8nK3WAZz7bP++zrte+swDGlGP0kDhmNpgLyVrLl 0gquN0L9QSj6KzpPCDB6YtonovHwCjkRuwrV/ft7++eNmH8/jssZijgKHt1O3FJ2NJ 5HHzk5JnBu5Ng== 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 , Alexandru Elisei Subject: [PATCH v3 18/36] KVM: arm64: Inject SIGSEGV on illegal accesses Date: Thu, 5 Mar 2026 14:43:31 +0000 Message-ID: <20260305144351.17071-19-will@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260305144351.17071-1-will@kernel.org> References: <20260305144351.17071-1-will@kernel.org> Precedence: bulk X-Mailing-List: kvmarm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 | 37 +++++++++++++++++++++++++++ arch/arm64/mm/fault.c | 22 ++++++++++++++++ 2 files changed, 59 insertions(+) diff --git a/arch/arm64/kvm/hyp/nvhe/mem_protect.c b/arch/arm64/kvm/hyp/nvhe/mem_protect.c index 31b6a52e5e4c..0dc1d6fc546c 100644 --- a/arch/arm64/kvm/hyp/nvhe/mem_protect.c +++ b/arch/arm64/kvm/hyp/nvhe/mem_protect.c @@ -18,6 +18,7 @@ #include #include #include +#include #define KVM_HOST_S2_FLAGS (KVM_PGTABLE_S2_AS_S1 | KVM_PGTABLE_S2_IDMAP) @@ -612,6 +613,39 @@ static int host_stage2_idmap(u64 addr) return ret; } +static void host_inject_mem_abort(struct kvm_cpu_context *host_ctxt) +{ + u64 ec, esr, spsr; + + esr = read_sysreg_el2(SYS_ESR); + spsr = read_sysreg_el2(SYS_SPSR); + + /* 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; + inject_host_exception(esr); +} + void handle_host_mem_abort(struct kvm_cpu_context *host_ctxt) { struct kvm_vcpu_fault_info fault; @@ -635,6 +669,9 @@ 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_mem_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..3abfc7272d63 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_mem_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)) -- 2.53.0.473.g4a7958ca14-goog