From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 E749D468C12; Mon, 14 Sep 2026 12:50:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789390209; cv=none; b=P/CfFwKRGXaIEj+FS2xahgdyuJep9R07/Na1rUudcYyYLfMjE9JOVAE+Cmc+Kb+J38EMXVrxiYFfr1oNNormyw+9cnGLky5JgI/gpLvLX28DYnLpkB8eKqyN2eZJOUZP/zbzkxj2xgT0SUHK8I0+fQR3aInkNuCVJFk2sOsVNGo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789390209; c=relaxed/simple; bh=J5+LWQZ2Pw7GZdx7OrTUfZuKENGPDom0WJ29M3Y/A08=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=HgGv7fm/ggQftjF0PwF48OGtMkpyy2xbDPW8rof6HvYfVQoiqCVJzFm+3s1NrovBXNf9R3zZhGk/cyB1XyqdnaHMPXanvGVaq0yP4MQBuyKYZxLXvnKvO+f/ZRYO5xODFVwLCiHnW7UgGFpt6guDJU/9XzfFakXJ4GKq5UCjycM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Kzv3MTv9; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="Kzv3MTv9" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 35D411F008A0; Mon, 14 Sep 2026 12:50:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1789390206; bh=M67P/7heE2Mo2dh13Rp/Xbz4pdwd47nfGB122TYaZO8=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=Kzv3MTv9G365yCOp7cZk3m1qFsw9IR5dpIVAnxfe4qVYWb14sEDkTI0ECSuAAWVQm CU61ag/pNTMR0KU5S81okPgXIdzr1bygNHPMmiE47jbqBgQhlngXu4C5C+mQrV2oix BWbfn2onei0y0BqdzrFo9hyQe/gx/L1EECESRD1wYB1mNkWZpAquM0OVmeqevF5d1F OBng9K8VTMPr814/qM5ZM+nLn0rxNk8XXjaGNiajfjhklt24WvW9fPSJ9SD5UwqFCN 9sk4ZO1kMNy9EAYZjGMfAzxXOIAN9A4jfJZ+EUkpN7d4FfSdrb6TcrOXIO60uHMxnz 7OomvAb31F3Zw== From: "Masami Hiramatsu (Google)" To: Steven Rostedt , Peter Zijlstra , Ingo Molnar , x86@kernel.org Cc: Jinchao Wang , Mathieu Desnoyers , Masami Hiramatsu , Thomas Gleixner , Borislav Petkov , Dave Hansen , "H . Peter Anvin" , Alexander Shishkin , Ian Rogers , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-perf-users@vger.kernel.org, Sean Christopherson , Paolo Bonzini , kvm@vger.kernel.org Subject: [PATCH v16 02/13] KVM: x86: Prevent host DR7 debug register leak into guest OS on NMI Date: Mon, 14 Sep 2026 21:49:59 +0900 Message-ID: <178939019982.94750.4441254006258061798.stgit@devnote2> X-Mailer: git-send-email 2.43.0 In-Reply-To: <178939017565.94750.9431053336761330458.stgit@devnote2> References: <178939017565.94750.9431053336761330458.stgit@devnote2> User-Agent: StGit/0.19 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit From: Masami Hiramatsu (Google) When KVM enters a guest OS, host hardware breakpoints are disabled before running the guest. However, an NMI can occur during guest execution, where local_db_save() or arch_install_hw_breakpoint() can be invoked. In particular, if local_db_save() or arch_install_hw_breakpoint() is executed from NMI, hardware DR7 can be modified or restored with host breakpoint settings, leaking host breakpoints into the guest OS or clobbering the guest's debug registers. Introduce a per-CPU flag, cpu_dr_in_guest, to indicate that the CPU is executing in guest mode. Set this flag in vcpu_enter_guest() during entering the guest with disabling host breakpoints. If this flag is set, local_db_save() and local_db_restore() return immediately, and arch_install_hw_breakpoint() returns an error. In addition, protect cpu_dr_in_guest in within_cpu_entry() to prevent recursive #DB exceptions. Fixes: f85d40160691 ("KVM: X86: Disable hardware breakpoints unconditionally before kvm_x86->run()") Assisted-by: Antigravity:gemini-3.8-flash Signed-off-by: Masami Hiramatsu (Google) --- Changes in v16: - Newly added. --- arch/x86/include/asm/debugreg.h | 6 ++++++ arch/x86/kernel/hw_breakpoint.c | 10 ++++++++++ arch/x86/kvm/x86.c | 7 +++++++ 3 files changed, 23 insertions(+) diff --git a/arch/x86/include/asm/debugreg.h b/arch/x86/include/asm/debugreg.h index 854d82b88ff4..50f830972698 100644 --- a/arch/x86/include/asm/debugreg.h +++ b/arch/x86/include/asm/debugreg.h @@ -18,6 +18,7 @@ #define DR7_FIXED_1 0x00000400 DECLARE_PER_CPU(unsigned long, cpu_dr7); +DECLARE_PER_CPU(bool, cpu_dr_in_guest); #ifndef CONFIG_PARAVIRT_XXL /* @@ -129,6 +130,9 @@ static __always_inline unsigned long local_db_save(void) { unsigned long dr7; + if (this_cpu_read(cpu_dr_in_guest)) + return 0; + if (cpu_feature_enabled(X86_FEATURE_HYPERVISOR) && !hw_breakpoint_active()) return 0; @@ -157,6 +161,8 @@ static __always_inline void local_db_restore(unsigned long dr7) * not be good. */ barrier(); + if (this_cpu_read(cpu_dr_in_guest)) + return; if (dr7) set_debugreg(dr7, 7); } diff --git a/arch/x86/kernel/hw_breakpoint.c b/arch/x86/kernel/hw_breakpoint.c index f846c15f21ca..68de7ed79d88 100644 --- a/arch/x86/kernel/hw_breakpoint.c +++ b/arch/x86/kernel/hw_breakpoint.c @@ -40,6 +40,9 @@ DEFINE_PER_CPU(unsigned long, cpu_dr7); EXPORT_PER_CPU_SYMBOL(cpu_dr7); +DEFINE_PER_CPU(bool, cpu_dr_in_guest); +EXPORT_PER_CPU_SYMBOL_GPL(cpu_dr_in_guest); + /* Per cpu debug address registers values */ static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]); @@ -102,6 +105,9 @@ int arch_install_hw_breakpoint(struct perf_event *bp) lockdep_assert_irqs_disabled(); + if (this_cpu_read(cpu_dr_in_guest)) + return -EBUSY; + for (i = 0; i < HBP_NUM; i++) { struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]); @@ -316,6 +322,10 @@ static inline bool within_cpu_entry(unsigned long addr, unsigned long end) if (within_area(addr, end, (unsigned long)&per_cpu(cpu_dr7, cpu), sizeof(cpu_dr7))) return true; + if (within_area(addr, end, + (unsigned long)&per_cpu(cpu_dr_in_guest, cpu), + sizeof(cpu_dr_in_guest))) + return true; } return false; diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 79468ddfe473..5e046924ab76 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8318,6 +8318,9 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_load_xfeatures(vcpu, true); + this_cpu_write(cpu_dr_in_guest, true); + barrier(); + if (unlikely(vcpu->arch.switch_db_regs && !(vcpu->arch.switch_db_regs & KVM_DEBUGREG_AUTO_SWITCH))) { set_debugreg(DR7_FIXED_1, 7); @@ -8400,6 +8403,10 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) kvm_update_dr7(vcpu); } + barrier(); + this_cpu_write(cpu_dr_in_guest, false); + barrier(); + /* * If the guest has used debug registers, at least dr7 * will be disabled while returning to the host.