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 8C2303328EE; Fri, 17 Oct 2025 15:02:37 +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=1760713357; cv=none; b=KZxK/uSipCyuzA+cHoDAezQJgEXGcun1DfUANjwf3cGNfcboUASx1TEgSFdzEqpwxrPIcxK2yqG8fIfgh+M26uqazhzCg/QrizvtiqcOMz8JU/KT2/llzztczboHsB0cNPw3g4KNYvC6X9wTIiQm67N+auKbzQiK604tmkAn7IY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760713357; c=relaxed/simple; bh=UPmKGknb+K7BifERug2FX2igtQrkzVmiJACqiRUs7K0=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=bbfIYIMUkz4IbpOpjbjOFykVUrx2tnjDYQgBXfYfri/x9+GAUPEKEjR6teD1KZKrk0dL0bpor2NPtGz3bf5DoO5VL64gkWS48Z0Y53RQlUXcrzp408w9/pTMvdoW+HG4py3BdJF7ARdiud7Zemk7GjW7Mbf3wRAXMMGKxYLSE5g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=DGvBlgpt; 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="DGvBlgpt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 14FB8C4CEE7; Fri, 17 Oct 2025 15:02:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1760713357; bh=UPmKGknb+K7BifERug2FX2igtQrkzVmiJACqiRUs7K0=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=DGvBlgptboY60Hb6/igyeqPvr2p3rLJlSdYiLpQpkUE2C1+bD9Qxrj2elCc+fdhBJ DWZRdYd32oU42WplHrlOwVFHR28PM/mf5eARt5dKpwzl4mWttB/5VDsxy4lpABLeVX Z3Tu3ecGSi7B783gglA01+MyFkQosJzhATzZdEUA= 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 , Sasha Levin Subject: [PATCH 6.1 138/168] KVM: x86: Dont (re)check L1 intercepts when completing userspace I/O Date: Fri, 17 Oct 2025 16:53:37 +0200 Message-ID: <20251017145134.113541006@linuxfoundation.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20251017145129.000176255@linuxfoundation.org> References: <20251017145129.000176255@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.1-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Greg Kroah-Hartman --- 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(-) --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5478,12 +5478,11 @@ 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; - unsigned emul_flags; ctxt->mem_read.pos = 0; @@ -5497,8 +5496,6 @@ int x86_emulate_insn(struct x86_emulate_ 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)) || @@ -5532,7 +5529,7 @@ int x86_emulate_insn(struct x86_emulate_ 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) @@ -5561,7 +5558,7 @@ int x86_emulate_insn(struct x86_emulate_ 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) @@ -5615,7 +5612,7 @@ int x86_emulate_insn(struct x86_emulate_ 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) --- a/arch/x86/kvm/kvm_emulate.h +++ b/arch/x86/kvm/kvm_emulate.h @@ -517,7 +517,7 @@ 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 @@ -8976,7 +8976,14 @@ 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;