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 0CD7E202997 for ; Mon, 13 Oct 2025 19:30:12 +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=1760383812; cv=none; b=GHSpwCCiY3IyupzOQYOkK3NG2Xs2QXiUQGUtVKyKkour9q2sSTh2LYvg8z1h15F6TigYMSs7IA0JyWTdhiH+tY/6FcBJjzKr9D1zCupJlwsyxZPd4yzqvVfgqP8ksETgeOvn8lVUAGs0COncZ2hhDzLvnOPujWXTbfJZG3oHQik= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1760383812; c=relaxed/simple; bh=sGMWwAB/pM3wc5UMlRwvhLCPKJKicPgPleX7t8Keogk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=J02TcbkTNJH78gu3vvTcCvBSp9oEj38GLZNhgIGVsgGyZl6jKzHQ9tO3vXS12yrhR/mn6cGhsY1/0moFmRLTqvk4ir39TmgThE9lRI5xVkI4ugj1c5GeujDcqsUU6f4v+rNEsqKG4FxqCqCN1HDpD7uXErNd+zBAqjOle2dP5T8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FzVog7SC; 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="FzVog7SC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 463B4C4CEE7; Mon, 13 Oct 2025 19:30:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1760383811; bh=sGMWwAB/pM3wc5UMlRwvhLCPKJKicPgPleX7t8Keogk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FzVog7SC6+JtMrXwnjMtDdayCUavHEAuj8za9xCd0Svc4ipgpRUoFYnvpil2lz/XK nMmU+rrqfFuPd1+4C23kuGxD3avGlzQ+4QWyub75Y4wD7HLVXtlp9ccib5/5ODu59s H4k7o8ss1dpUKNB/iFQ9JfX6hiYvzowxeYH3dEl7wMEimKZRQRtU243WQ16lMkmHBR e0hDYJWeEqlyaUfeODokDfzKM3KOR2KlX70Qn4g9qbvF0h0vvhqJS9lmu5Yu+mZgOb ZV9SjPRNX5sASpQ13Zt2x1QT3fzA0snfovhLnRnA0+cKBFYdl9YsJgze6GfCraN0QJ cPQ6A0fjZYv+Q== From: Sasha Levin To: stable@vger.kernel.org Cc: Sean Christopherson , syzbot+cc2032ba16cc2018ca25@syzkaller.appspotmail.com, Jim Mattson , Sasha Levin Subject: [PATCH 5.4.y] KVM: x86: Don't (re)check L1 intercepts when completing userspace I/O Date: Mon, 13 Oct 2025 15:30:09 -0400 Message-ID: <20251013193009.3567346-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025101008-embezzle-energize-3957@gregkh> References: <2025101008-embezzle-energize-3957@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/include/asm/kvm_emulate.h | 2 +- arch/x86/kvm/emulate.c | 10 ++++------ arch/x86/kvm/x86.c | 9 ++++++++- 3 files changed, 13 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/kvm_emulate.h b/arch/x86/include/asm/kvm_emulate.h index 77cf6c11f66bd..f8e8799a8757d 100644 --- a/arch/x86/include/asm/kvm_emulate.h +++ b/arch/x86/include/asm/kvm_emulate.h @@ -448,7 +448,7 @@ 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/emulate.c b/arch/x86/kvm/emulate.c index 1a9fa29038526..90c495b870702 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -5605,12 +5605,11 @@ 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; @@ -5625,7 +5624,6 @@ int x86_emulate_insn(struct x86_emulate_ctxt *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)) || @@ -5659,7 +5657,7 @@ int x86_emulate_insn(struct x86_emulate_ctxt *ctxt) fetch_possible_mmx_operand(ctxt, &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) @@ -5688,7 +5686,7 @@ 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) @@ -5742,7 +5740,7 @@ 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/x86.c b/arch/x86/kvm/x86.c index 8eb62dbb3a186..9c53bc25aa36d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6855,7 +6855,14 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, /* Save the faulting GPA (cr2) in the address field */ ctxt->exception.address = cr2_or_gpa; - 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