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 BC33226A0A7 for ; Mon, 13 Apr 2026 15:20:07 +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=1776093607; cv=none; b=D3kxYAj2++m7i+GzmjQYL+TQFN8wO+KOcKwnWSRKXrAs1f7W4Bt56XoX6uYn9jLoSFJtaxfh0PeS04UXpnFGvbUyKHZvuGZW0B4NXuEmg4U0z7gZH3UIYvvGqLs3kV302cYdvBwOnoldAZ5IqCOPPEqNBIPxuqpJbkBYiQMiC4Y= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776093607; c=relaxed/simple; bh=ccEzDE7Ie2+I5L7kp/p7Uq3EjObgwxNlw+lEWctjwWU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=eqPQvQXjL0/snQpGvfGxEKg0phwKDMwB9Tr/iNIRV062LfYJ1jxfotSmWwrxkhFlwdWv3sH+8+4FmaT5AwqjDCAG3fyD0U3ZoNaDov3UoW0DTn35VSjecZlrBUh+2i4H5CLcFEziB4JBesXsQOmAjHWo0yFI6NutsQNtWur2HTA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ony/0bUf; 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="ony/0bUf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D65F9C2BCAF; Mon, 13 Apr 2026 15:20:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776093607; bh=ccEzDE7Ie2+I5L7kp/p7Uq3EjObgwxNlw+lEWctjwWU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ony/0bUfPn07wAfHlDRhOsh/7D2PUKhiUKRUHgOihi9J7o/bu/1BY3nGc0KHYMUVA +HPkafifzS6zTkoRFjYoI/MkSGbhxN+oe7XQZx2NYJST2oK1r/T9LJKaFwwRyZJa6y /OHvc16JzOe1RqjtcGWsDn6mcFpp9EL53a4QqgInjXPAsaX/sCDEjbio0wnb5Kjakt up6Amk396vbEZjm4if69t0S40AK6zbUXGLbGxNnw61BzGBHkd/3LhynJ7b1eM33/P8 nGkxGJna3PXh7Y+BLyRBBb74vVq3HnMlVft2Mu8EH65bxvGzOWAfUbQBZhqWrLPvvb ntcHalr+Q7rLQ== From: Sasha Levin To: stable@vger.kernel.org Cc: David Woodhouse , Sean Christopherson , Sasha Levin Subject: [PATCH 6.1.y] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs Date: Mon, 13 Apr 2026 11:20:05 -0400 Message-ID: <20260413152005.3014972-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026041319-perceive-bok-f424@gregkh> References: <2026041319-perceive-bok-f424@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: 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 [ applied `__DECLARE_FLEX_ARRAY(char, name)` change directly instead of inside missing `#ifdef __KERNEL__` else branch ] 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 46de10a809ecb..c4ca3fb749e01 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -198,13 +198,13 @@ 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 */ @@ -241,7 +241,7 @@ 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 { @@ -263,7 +263,7 @@ 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 */ @@ -394,7 +394,7 @@ 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 @@ -522,7 +522,7 @@ 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 0d5d4419139ae..79b4c194b262f 100644 --- a/include/uapi/linux/kvm.h +++ b/include/uapi/linux/kvm.h @@ -11,6 +11,7 @@ #include #include #include +#include #include #include @@ -556,7 +557,7 @@ 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 \ @@ -635,7 +636,7 @@ 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 */ @@ -1242,7 +1243,7 @@ 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); }; #endif @@ -1362,7 +1363,7 @@ struct kvm_dirty_tlb { struct kvm_reg_list { __u64 n; /* number of regs */ - __u64 reg[]; + __DECLARE_FLEX_ARRAY(__u64, reg); }; struct kvm_one_reg { @@ -2183,7 +2184,7 @@ struct kvm_stats_desc { __u16 size; __u32 offset; __u32 bucket_size; - char name[]; + __DECLARE_FLEX_ARRAY(char, name); }; #define KVM_GET_STATS_FD _IO(KVMIO, 0xce) -- 2.53.0