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 0A3ED13AD26 for ; Mon, 13 Oct 2025 17:36:44 +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=1760377005; cv=none; b=E2NVJl8cgkyB72J/ifTBLAFFhBFgQnxGXrGobGTKCN0/00DBR/GnW3brCpuUYwsUkfa4LVzWQfSZoSApUoeMvB6Rp/xQmSvhtg16Xq4nFvmRsa8F26GT9Hbpmd71t96OvNlu4Tu8yIKFgtq2B0mx43l6+u3756aDk27e0z0C/Yg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760377005; c=relaxed/simple; bh=yfryrst7aMAI7pNNcfPWfpYJk1n7ro4eOjd5sJGJuLM=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=ScZ6ubAqq+HleWi0a4eF9meSgwBvFpCHLvbmGahOOSIKhrLoAjo/zzsLYVuaiZZGpaIfTuumTriGjHs4tnEZxRmnB/BjLwuEdB1MYMjfvkVhrUbQdhQZ4HYUmJaDs3z8bVUielZKg5cDgmlFtDFX3nIGTgHfpyLppy/44/zc3PY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GsRSYJnm; 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="GsRSYJnm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F321CC4CEE7; Mon, 13 Oct 2025 17:36:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760377004; bh=yfryrst7aMAI7pNNcfPWfpYJk1n7ro4eOjd5sJGJuLM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=GsRSYJnmAYGKSsrJhkKfpK5DYtwYSYAo21mzJalIYZ94ZUU/X34MQ7msjKKhKTpn8 a5mQ9LZzdDys+wcBfXWtDaCgx/nB2foFZBZ42C7kpkeLu2gZwANdbVlWaVTHrNYtOG 3RjaF/4AYP415F35Ux500oROTwQg6z/L3msD2xf1k7GfZjnpUsBiTY7skMoxjuVSI+ 32xXjtz6wd6+mBe8kFsfG8wmOBQomkRYPLjWwwHCs51j6164raKxx0uICBSqIXPd0S l6jH/qJNWapkbvyUQmmLTo3fz0PdrG1XkIFse787QLYAfyK4nDaDgaP9pm50jPqLvG ln1keGLpyIiWg== From: Sasha Levin To: stable@vger.kernel.org Cc: Sean Christopherson , syzbot+cc2032ba16cc2018ca25@syzkaller.appspotmail.com, Jim Mattson , Sasha Levin Subject: [PATCH 5.15.y] KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O Date: Mon, 13 Oct 2025 13:36:41 -0400 Message-ID: <20251013173641.3404405-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025101006-moonwalk-smilingly-3725@gregkh> References: <2025101006-moonwalk-smilingly-3725@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Sean Christopherson [ Upstream commit e750f85391286a4c8100275516973324b621a269 ] 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 [ is_guest_mode() was open coded ] Signed-off-by: Sasha Levin --- arch/x86/kvm/emulate.c | 11 ++++------- arch/x86/kvm/kvm_emulate.h | 2 +- arch/x86/kvm/x86.c | 9 ++++++++- 3 files changed, 13 insertions(+), 9 deletions(-) diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 98b25a7af8ce8..dae68691f4248 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5452,12 +5452,11 @@ void init_decode_cache(struct x86_emulate_ctxt *ctxt) 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; - unsigned emul_flags; ctxt->mem_read.pos = 0; @@ -5471,8 +5470,6 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) rc = emulate_ud(ctxt); goto done; } - - emul_flags = ctxt->ops->get_hflags(ctxt); if (unlikely(ctxt->d & (No64|Undefined|Sse|Mmx|Intercept|CheckPerm|Priv|Prot|String))) { if ((ctxt->mode == X86EMUL_MODE_PROT64 && (ctxt->d & No64)) || @@ -5506,7 +5503,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) fetch_possible_mmx_operand(&ctxt->dst); } - if (unlikely(emul_flags & X86EMUL_GUEST_MASK) && ctxt->intercept) { + if (unlikely(check_intercepts) && ctxt->intercept) { rc = emulator_check_intercept(ctxt, ctxt->intercept, X86_ICPT_PRE_EXCEPT); if (rc != X86EMUL_CONTINUE) @@ -5535,7 +5532,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) goto done; } - if (unlikely(emul_flags & X86EMUL_GUEST_MASK) && (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) @@ -5589,7 +5586,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) special_insn: - if (unlikely(emul_flags & X86EMUL_GUEST_MASK) && (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) diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h index fb09cd22cb7f5..6507340513cdd 100644 --- a/arch/x86/kvm/kvm_emulate.h +++ b/arch/x86/kvm/kvm_emulate.h @@ -496,7 +496,7 @@ bool x86_page_table_writing_insn(struct x86_emulate_ctxt *ctxt); #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); diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2ba297da7bdec..648f80f73e66c 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8209,7 +8209,14 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, 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; -- 2.51.0