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 29D2882899; Sun, 1 Mar 2026 01:31:15 +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=1772328675; cv=none; b=NYxtf7KdeMW6rGQMlt/Peh8bmGoIDdlmsfU0tFrMcLYNGYmr3L/XZExkMoqdtmAgoFt0M1fT1ps9ydG5YMOkATHhKKFNzQb3zf62EFzOIOE1URjHZ6uXgUC4C6nxF3GqdaDSREMnCDuVYL/ScZLbRmffvjjIDJ3UY3LE9EHu6Bg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772328675; c=relaxed/simple; bh=8bb/Me4499dWoX8UJjOmDFjDFiMysoGa7pT3I9yCcas=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=flZbOtmYKU2iMm6ON7RZhO7R85XcCAlvis5JulTahhWHOCp6aMnCOwDNuiIg0xWJ+Cv9K53QJ5eqj8ETyQCjMaWNi+Xg60kWrhBdmtvjMy6ikDWvhPcgwiP65uUmvC2Gep/92lCJyYWlcvffTyhm0T851gl27rtD0TZRboj+t4M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=GDru5KG1; 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="GDru5KG1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 90560C19424; Sun, 1 Mar 2026 01:31:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772328675; bh=8bb/Me4499dWoX8UJjOmDFjDFiMysoGa7pT3I9yCcas=; h=From:To:Cc:Subject:Date:From; b=GDru5KG1KhLBjyPmW3o+wG0xIdYP25WMWCbWDROwwUo8Ubx74tmeUBQmkpd2bduxR Vz12kFBZEfJBiO4e+YixflsCGLL6iZQ6B7QmhwFcX1REXi7iitE4uKtfAIsy5vW39F H9OhjBCryTJHrAAprWt0lP5lvpFplyc0CbPCH8lONTjmhoxPYQ18EeYR3Ge4OdG+Hq xtdy5K0iJz532S+X/rwJknIm3oSxYOno5vBMQ7gnnKAQucx942NC7F2sPAYGUi0oZE c1zzxSUqVgQ8gJYQtej6IXWgFl9oThpFhu7YA7OKOZ5PoCqo43J5mfAoleYCjdr026 spiwnu1H+XX0A== From: Sasha Levin To: stable@vger.kernel.org, seanjc@google.com Cc: Yosry Ahmed , kvm@vger.kernel.org Subject: FAILED: Patch "KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding" failed to apply to 6.6-stable tree Date: Sat, 28 Feb 2026 20:31:13 -0500 Message-ID: <20260301013113.1689664-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Patchwork-Hint: ignore X-stable: review Content-Transfer-Encoding: 8bit The patch below does not apply to the 6.6-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to . Thanks, Sasha ------------------ original commit in Linus's tree ------------------ >From fc3ba56385d03501eb582e4b86691ba378e556f9 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Tue, 16 Dec 2025 08:17:54 -0800 Subject: [PATCH] KVM: nSVM: Remove a user-triggerable WARN on nested_svm_load_cr3() succeeding Drop the WARN in svm_set_nested_state() on nested_svm_load_cr3() failing as it is trivially easy to trigger from userspace by modifying CPUID after loading CR3. E.g. modifying the state restoration selftest like so: --- tools/testing/selftests/kvm/x86/state_test.c +++ tools/testing/selftests/kvm/x86/state_test.c @@ -280,7 +280,16 @@ int main(int argc, char *argv[]) /* Restore state in a new VM. */ vcpu = vm_recreate_with_one_vcpu(vm); - vcpu_load_state(vcpu, state); + + if (stage == 4) { + state->sregs.cr3 = BIT(44); + vcpu_load_state(vcpu, state); + + vcpu_set_cpuid_property(vcpu, X86_PROPERTY_MAX_PHY_ADDR, 36); + __vcpu_nested_state_set(vcpu, &state->nested); + } else { + vcpu_load_state(vcpu, state); + } /* * Restore XSAVE state in a dummy vCPU, first without doing generates: WARNING: CPU: 30 PID: 938 at arch/x86/kvm/svm/nested.c:1877 svm_set_nested_state+0x34a/0x360 [kvm_amd] Modules linked in: kvm_amd kvm irqbypass [last unloaded: kvm] CPU: 30 UID: 1000 PID: 938 Comm: state_test Tainted: G W 6.18.0-rc7-58e10b63777d-next-vm Tainted: [W]=WARN Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 0.0.0 02/06/2015 RIP: 0010:svm_set_nested_state+0x34a/0x360 [kvm_amd] Call Trace: kvm_arch_vcpu_ioctl+0xf33/0x1700 [kvm] kvm_vcpu_ioctl+0x4e6/0x8f0 [kvm] __x64_sys_ioctl+0x8f/0xd0 do_syscall_64+0x61/0xad0 entry_SYSCALL_64_after_hwframe+0x4b/0x53 Simply delete the WARN instead of trying to prevent userspace from shoving "illegal" state into CR3. For better or worse, KVM's ABI allows userspace to set CPUID after SREGS, and vice versa, and KVM is very permissive when it comes to guest CPUID. I.e. attempting to enforce the virtual CPU model when setting CPUID could break userspace. Given that the WARN doesn't provide any meaningful protection for KVM or benefit for userspace, simply drop it even though the odds of breaking userspace are minuscule. Opportunistically delete a spurious newline. Fixes: b222b0b88162 ("KVM: nSVM: refactor the CR3 reload on migration") Cc: stable@vger.kernel.org Cc: Yosry Ahmed Reviewed-by: Yosry Ahmed Link: https://patch.msgid.link/20251216161755.1775409-1-seanjc@google.com Signed-off-by: Sean Christopherson --- arch/x86/kvm/svm/nested.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c index ba0f11c68372b..9be67040e94d9 100644 --- a/arch/x86/kvm/svm/nested.c +++ b/arch/x86/kvm/svm/nested.c @@ -1870,10 +1870,9 @@ static int svm_set_nested_state(struct kvm_vcpu *vcpu, * thus MMU might not be initialized correctly. * Set it again to fix this. */ - ret = nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3, nested_npt_enabled(svm), false); - if (WARN_ON_ONCE(ret)) + if (ret) goto out_free; svm->nested.force_msr_bitmap_recalc = true; -- 2.51.0