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 3F7B93603E1 for ; Mon, 13 Apr 2026 13:01:29 +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=1776085289; cv=none; b=Z0uNprERVdJPRqkf6Vh2WYZSbPG682V26Vjc2AO5FCNTTy9pq0OMZD65e6OxitYaoqI7vAQ1SmO3aX3TCz/vTklLC4U8qKwxMHjkR8VWnAZCgOArVEkuHvJf9D67mM8uXFdUbkLOnpmpj6JmmRsdWnG+zpiQRwmVB8zCByGeqsY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776085289; c=relaxed/simple; bh=wN8KeJj0Nz/xcVtX2VAq4K76CSQR/dA0n5RLYMaBy0g=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=GKB60hYYeG4MVvYuhcC4KiqfGdBnGXy4rDfvGi2iZAQK9FYh0XfTh3yEYc2er5+zwDYZO5pXOXGCQtVu9XBuTiddhnZlstCP3do0TP26/7D5J4BVFPskatAnByAdWWMGn43KZYElpKujyHPTPWgqnxIn4kfZnV44nOnVl2VGU0Q= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gb3CewOV; 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="gb3CewOV" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 63764C2BCB5; Mon, 13 Apr 2026 13:01:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776085288; bh=wN8KeJj0Nz/xcVtX2VAq4K76CSQR/dA0n5RLYMaBy0g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gb3CewOV91FGrbtv950pfXYQQ80nxn2rvGJcHF+GtNpY2A+42jsZyb8+1cmLwlxcv 1mmO69A238DuPC9wh7j34bXQOgmqJG8EKDhvNw36ozZ0mJQZawafHcc0s8haXaXwpw VqhBLEr2wWKvqTivERirbw6peUthtsW4QziSScRcLTgCJ96H6mrpgrx4ZngDD1ZSko nGZr8hnaRHmDMp9RmhrBnXn70x/h07/o9eQf9AO0rASqkQMgZw9zNMUzgiJSLZDl/9 doTXml88ru4FGtPtb7aOieAM2TABs5a5C6sl6hbHyVu2kBVC8GIsiVmFY/OevlsKJS UQKd/vf6Ya+OQ== From: Sasha Levin To: stable@vger.kernel.org Cc: David Woodhouse , Sean Christopherson , Sasha Levin Subject: [PATCH 6.18.y 2/2] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs Date: Mon, 13 Apr 2026 09:01:25 -0400 Message-ID: <20260413130125.2879436-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260413130125.2879436-1-sashal@kernel.org> References: <2026041317-engaged-onset-3db3@gregkh> <20260413130125.2879436-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: David Woodhouse [ Upstream commit 2619da73bb2f10d88f7e1087125c40144fdf0987 ] Commit 94dfc73e7cf4 ("treewide: uapi: Replace zero-length arrays with flexible-array members") broke the userspace API for C++. These structures ending in VLAs are typically a *header*, which can be followed by an arbitrary number of entries. Userspace typically creates a larger structure with some non-zero number of entries, for example in QEMU's kvm_arch_get_supported_msr_feature(): struct { struct kvm_msrs info; struct kvm_msr_entry entries[1]; } msr_data = {}; While that works in C, it fails in C++ with an error like: flexible array member 'kvm_msrs::entries' not at end of 'struct msr_data' Fix this by using __DECLARE_FLEX_ARRAY() for the VLA, which uses [0] for C++ compilation. Fixes: 94dfc73e7cf4 ("treewide: uapi: Replace zero-length arrays with flexible-array members") Cc: stable@vger.kernel.org Signed-off-by: David Woodhouse Link: https://patch.msgid.link/3abaf6aefd6e5efeff3b860ac38421d9dec908db.camel@infradead.org [sean: tag for stable@] Signed-off-by: Sean Christopherson Signed-off-by: Sasha Levin --- arch/x86/include/uapi/asm/kvm.h | 12 ++++++------ include/uapi/linux/kvm.h | 11 ++++++----- 2 files changed, 12 insertions(+), 11 deletions(-) diff --git a/arch/x86/include/uapi/asm/kvm.h b/arch/x86/include/uapi/asm/kvm.h index 42e4e835a7b42..67b3bea44c674 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -197,13 +197,13 @@ struct kvm_msrs { __u32 nmsrs; /* number of msrs in entries */ __u32 pad; - struct kvm_msr_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_msr_entry, entries); }; /* for KVM_GET_MSR_INDEX_LIST */ struct kvm_msr_list { __u32 nmsrs; /* number of msrs in entries */ - __u32 indices[]; + __DECLARE_FLEX_ARRAY(__u32, indices); }; /* Maximum size of any access bitmap in bytes */ @@ -245,7 +245,7 @@ struct kvm_cpuid_entry { struct kvm_cpuid { __u32 nent; __u32 padding; - struct kvm_cpuid_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_cpuid_entry, entries); }; struct kvm_cpuid_entry2 { @@ -267,7 +267,7 @@ struct kvm_cpuid_entry2 { struct kvm_cpuid2 { __u32 nent; __u32 padding; - struct kvm_cpuid_entry2 entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_cpuid_entry2, entries); }; /* for KVM_GET_PIT and KVM_SET_PIT */ @@ -398,7 +398,7 @@ struct kvm_xsave { * the contents of CPUID leaf 0xD on the host. */ __u32 region[1024]; - __u32 extra[]; + __DECLARE_FLEX_ARRAY(__u32, extra); }; #define KVM_MAX_XCRS 16 @@ -564,7 +564,7 @@ struct kvm_pmu_event_filter { __u32 fixed_counter_bitmap; __u32 flags; __u32 pad[4]; - __u64 events[]; + __DECLARE_FLEX_ARRAY(__u64, events); }; #define KVM_PMU_EVENT_ALLOW 0 diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h index f89e1500962cd..954e0511ce91c 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -523,7 +524,7 @@ struct kvm_coalesced_mmio { struct kvm_coalesced_mmio_ring { __u32 first, last; - struct kvm_coalesced_mmio coalesced_mmio[]; + __DECLARE_FLEX_ARRAY(struct kvm_coalesced_mmio, coalesced_mmio); }; #define KVM_COALESCED_MMIO_MAX \ @@ -573,7 +574,7 @@ struct kvm_clear_dirty_log { /* for KVM_SET_SIGNAL_MASK */ struct kvm_signal_mask { __u32 len; - __u8 sigset[]; + __DECLARE_FLEX_ARRAY(__u8, sigset); }; /* for KVM_TPR_ACCESS_REPORTING */ @@ -1029,7 +1030,7 @@ struct kvm_irq_routing_entry { struct kvm_irq_routing { __u32 nr; __u32 flags; - struct kvm_irq_routing_entry entries[]; + __DECLARE_FLEX_ARRAY(struct kvm_irq_routing_entry, entries); }; #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0) @@ -1120,7 +1121,7 @@ struct kvm_dirty_tlb { struct kvm_reg_list { __u64 n; /* number of regs */ - __u64 reg[]; + __DECLARE_FLEX_ARRAY(__u64, reg); }; struct kvm_one_reg { @@ -1575,7 +1576,7 @@ struct kvm_stats_desc { #ifdef __KERNEL__ char name[KVM_STATS_NAME_SIZE]; #else - char name[]; + __DECLARE_FLEX_ARRAY(char, name); #endif }; -- 2.53.0