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 1BC002F60CD; Fri, 10 Oct 2025 13:17:47 +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=1760102268; cv=none; b=ffvpzEyh3IRFcPHwWUwVXr008g7MUJM9ahPfh2Zcu1Jxy0QtO63PSIjLmV0wAYiAe6KBr+J6BOO74gULeNU4zDNTJ8gbT01F9QQpcjlGiAiwnR0GAWL5b6XltA7lagkh0Pl/o0zy7Ja58LK6hq0qLzcLX4+YEVFQiJUU5Gwvuig= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760102268; c=relaxed/simple; bh=+lEpebIQQsG1H1UCUOg/C87FCT+edxk9ywzHNJAPb1w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=oiGCOv+B9OKbvD989ZX7stFugIA84p2v7EcttvJREG/dMvWPBvts/+5BrHODj1qXzJBuYJp21BBPAfk3QiwtiannaLPrNxRRsHXW4rQvPuTZZJh6F4Ss1Xmu7wj0psj6aXg/mAR3mkTPNa2E9KEqdDQslrA9Q1aSeBB2zpfe8BM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=jWr9j7er; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="jWr9j7er" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4947FC4CEF9; Fri, 10 Oct 2025 13:17:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1760102267; bh=+lEpebIQQsG1H1UCUOg/C87FCT+edxk9ywzHNJAPb1w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jWr9j7er7NJ5aYj/laE2wy5GxqUUSU4bVl0vBSaHsXg+WC1zyS8BrD8W5+Bk6WvMV UWcq7FCqgRcukgkNtPQv/IS+sZS7B26v2EvvkLfI73qS0DMzvrEaQ3ZmSN3afaIOUG OOtGRnDldLb17GXqHFTv9aW0fCp2+P6uBYmz6wp0= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+cc2032ba16cc2018ca25@syzkaller.appspotmail.com, Jim Mattson , Sean Christopherson Subject: [PATCH 6.17 24/26] KVM: x86: Dont (re)check L1 intercepts when completing userspace I/O Date: Fri, 10 Oct 2025 15:16:19 +0200 Message-ID: <20251010131332.085052566@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251010131331.204964167@linuxfoundation.org> References: <20251010131331.204964167@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson commit e750f85391286a4c8100275516973324b621a269 upstream. When completing emulation of instruction that generated a userspace exit for I/O, don't recheck L1 intercepts as KVM has already finished that phase of instruction execution, i.e. has already committed to allowing L2 to perform I/O. If L1 (or host userspace) modifies the I/O permission bitmaps during the exit to userspace, KVM will treat the access as being intercepted despite already having emulated the I/O access. Pivot on EMULTYPE_NO_DECODE to detect that KVM is completing emulation. Of the three users of EMULTYPE_NO_DECODE, only complete_emulated_io() (the intended "recipient") can reach the code in question. gp_interception()'s use is mutually exclusive with is_guest_mode(), and complete_emulated_insn_gp() unconditionally pairs EMULTYPE_NO_DECODE with EMULTYPE_SKIP. The bad behavior was detected by a syzkaller program that toggles port I/O interception during the userspace I/O exit, ultimately resulting in a WARN on vcpu->arch.pio.count being non-zero due to KVM no completing emulation of the I/O instruction. WARNING: CPU: 23 PID: 1083 at arch/x86/kvm/x86.c:8039 emulator_pio_in_out+0x154/0x170 [kvm] Modules linked in: kvm_intel kvm irqbypass CPU: 23 UID: 1000 PID: 1083 Comm: repro Not tainted 6.16.0-rc5-c1610d2d66b1-next-vm #74 NONE Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:emulator_pio_in_out+0x154/0x170 [kvm] PKRU: 55555554 Call Trace: kvm_fast_pio+0xd6/0x1d0 [kvm] vmx_handle_exit+0x149/0x610 [kvm_intel] kvm_arch_vcpu_ioctl_run+0xda8/0x1ac0 [kvm] kvm_vcpu_ioctl+0x244/0x8c0 [kvm] __x64_sys_ioctl+0x8a/0xd0 do_syscall_64+0x5d/0xc60 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Reported-by: syzbot+cc2032ba16cc2018ca25@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/68790db4.a00a0220.3af5df.0020.GAE@google.com Fixes: 8a76d7f25f8f ("KVM: x86: Add x86 callback for intercept check") Cc: stable@vger.kernel.org Cc: Jim Mattson Link: https://lore.kernel.org/r/20250715190638.1899116-1-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Greg Kroah-Hartman --- arch/x86/kvm/emulate.c | 9 ++++----- arch/x86/kvm/kvm_emulate.h | 3 +-- arch/x86/kvm/x86.c | 15 ++++++++------- 3 files changed, 13 insertions(+), 14 deletions(-) --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5107,12 +5107,11 @@ void init_decode_cache(struct x86_emulat ctxt->mem_read.end = 0; } -int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) +int x86_emulate_insn(struct x86_emulate_ctxt *ctxt, bool check_intercepts) { const struct x86_emulate_ops *ops = ctxt->ops; int rc = X86EMUL_CONTINUE; int saved_dst_type = ctxt->dst.type; - bool is_guest_mode = ctxt->ops->is_guest_mode(ctxt); ctxt->mem_read.pos = 0; @@ -5160,7 +5159,7 @@ int x86_emulate_insn(struct x86_emulate_ fetch_possible_mmx_operand(&ctxt->dst); } - if (unlikely(is_guest_mode) && ctxt->intercept) { + if (unlikely(check_intercepts) && ctxt->intercept) { rc = emulator_check_intercept(ctxt, ctxt->intercept, X86_ICPT_PRE_EXCEPT); if (rc != X86EMUL_CONTINUE) @@ -5189,7 +5188,7 @@ int x86_emulate_insn(struct x86_emulate_ goto done; } - if (unlikely(is_guest_mode) && (ctxt->d & Intercept)) { + if (unlikely(check_intercepts) && (ctxt->d & Intercept)) { rc = emulator_check_intercept(ctxt, ctxt->intercept, X86_ICPT_POST_EXCEPT); if (rc != X86EMUL_CONTINUE) @@ -5243,7 +5242,7 @@ int x86_emulate_insn(struct x86_emulate_ special_insn: - if (unlikely(is_guest_mode) && (ctxt->d & Intercept)) { + if (unlikely(check_intercepts) && (ctxt->d & Intercept)) { rc = emulator_check_intercept(ctxt, ctxt->intercept, X86_ICPT_POST_MEMACCESS); if (rc != X86EMUL_CONTINUE) --- a/arch/x86/kvm/kvm_emulate.h +++ b/arch/x86/kvm/kvm_emulate.h @@ -235,7 +235,6 @@ struct x86_emulate_ops { void (*set_nmi_mask)(struct x86_emulate_ctxt *ctxt, bool masked); bool (*is_smm)(struct x86_emulate_ctxt *ctxt); - bool (*is_guest_mode)(struct x86_emulate_ctxt *ctxt); int (*leave_smm)(struct x86_emulate_ctxt *ctxt); void (*triple_fault)(struct x86_emulate_ctxt *ctxt); int (*set_xcr)(struct x86_emulate_ctxt *ctxt, u32 index, u64 xcr); @@ -521,7 +520,7 @@ bool x86_page_table_writing_insn(struct #define EMULATION_RESTART 1 #define EMULATION_INTERCEPTED 2 void init_decode_cache(struct x86_emulate_ctxt *ctxt); -int x86_emulate_insn(struct x86_emulate_ctxt *ctxt); +int x86_emulate_insn(struct x86_emulate_ctxt *ctxt, bool check_intercepts); int emulator_task_switch(struct x86_emulate_ctxt *ctxt, u16 tss_selector, int idt_index, int reason, bool has_error_code, u32 error_code); --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8470,11 +8470,6 @@ static bool emulator_is_smm(struct x86_e return is_smm(emul_to_vcpu(ctxt)); } -static bool emulator_is_guest_mode(struct x86_emulate_ctxt *ctxt) -{ - return is_guest_mode(emul_to_vcpu(ctxt)); -} - #ifndef CONFIG_KVM_SMM static int emulator_leave_smm(struct x86_emulate_ctxt *ctxt) { @@ -8558,7 +8553,6 @@ static const struct x86_emulate_ops emul .guest_cpuid_is_intel_compatible = emulator_guest_cpuid_is_intel_compatible, .set_nmi_mask = emulator_set_nmi_mask, .is_smm = emulator_is_smm, - .is_guest_mode = emulator_is_guest_mode, .leave_smm = emulator_leave_smm, .triple_fault = emulator_triple_fault, .set_xcr = emulator_set_xcr, @@ -9143,7 +9137,14 @@ restart: ctxt->exception.address = 0; } - r = x86_emulate_insn(ctxt); + /* + * Check L1's instruction intercepts when emulating instructions for + * L2, unless KVM is re-emulating a previously decoded instruction, + * e.g. to complete userspace I/O, in which case KVM has already + * checked the intercepts. + */ + r = x86_emulate_insn(ctxt, is_guest_mode(vcpu) && + !(emulation_type & EMULTYPE_NO_DECODE)); if (r == EMULATION_INTERCEPTED) return 1;