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 C1E3B3B3C18 for ; Mon, 13 Apr 2026 14:58:37 +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=1776092317; cv=none; b=AaH5TVAJEdM1l9yraGd9RfRS8bxIjsFebABUGEd1p2B5xYs38SaS+CMheM6op64WfbUIjyzPzLb22hlrgWacOIZkm1U7BkBWnaNr+fcXlsYlI4ObX+kMRP6te65rDKRQcNnw9gvp9BW1GyyRY+975DbHTFtv46jQ+JNSJ0hhI54= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1776092317; c=relaxed/simple; bh=+65Vb8ra+TrWyLvYxM2Xlt1rJf+nedmBZHlfHtmPGx4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lLEOaHbg7h7ShR58KHdmB3KeqvrzcNBrz4+OQdvnnEIO2XrGi2hkQn4d+1eHQ8mCaBZ/G1KUXWeJlI3BPCdVZUlUHK2JpRSIG6uigukmQqMxb4RYL51fh6Xte2G1qXEC4irMoMHtSQqOQqx2KLB/v6/EnW8kRYV1+3yusFblIcU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=Z1T3wObR; 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="Z1T3wObR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id EA5E3C2BCAF; Mon, 13 Apr 2026 14:58:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1776092317; bh=+65Vb8ra+TrWyLvYxM2Xlt1rJf+nedmBZHlfHtmPGx4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Z1T3wObRzVbzG8vYl6N8b2vEhhYfTuCX/LcsMP+c3vEeoqiOXqXzuEYzjc+0DWGT1 85lmAwTeWc0twzjw3/sfVx5I70b4ndwe0iCRsFkxGsfCV4fk3xRqYsgsTwRsEpZ4GG 9JEBribf7AwzqT+0/xcWBC4EUb5nSUXoGFsXm/9VhLMw4BisqoP7ut9qlxlwlswLTZ 80GfGCb0iE42L4XWGMCvCYEIYqwuCNyhJpMjbt9qiUJUYIqSvyqpuR1yfhyjDXTcPv jGAxrBkO5I5kxbFSYC7UMO57uVHyuwFwabBGvDScf0oxFMZ8P21YRSyFhr52w8IZQ0 QiibGi+WuijSQ== From: Sasha Levin To: stable@vger.kernel.org Cc: David Woodhouse , Sean Christopherson , Sasha Levin Subject: [PATCH 6.6.y] KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs Date: Mon, 13 Apr 2026 10:58:35 -0400 Message-ID: <20260413145835.2969194-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026041318-monogamy-woozy-29fe@gregkh> References: <2026041318-monogamy-woozy-29fe@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 1a6a1f9879496..07b5685d9c769 100644 --- a/arch/x86/include/uapi/asm/kvm.h +++ b/arch/x86/include/uapi/asm/kvm.h @@ -191,13 +191,13 @@ 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 */ @@ -239,7 +239,7 @@ 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 { @@ -261,7 +261,7 @@ 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 */ @@ -392,7 +392,7 @@ 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 @@ -520,7 +520,7 @@ 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 13065dd96132d..e48ba56c54858 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 \ @@ -643,7 +644,7 @@ 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 */ @@ -1256,7 +1257,7 @@ 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 @@ -1377,7 +1378,7 @@ struct kvm_dirty_tlb { struct kvm_reg_list { __u64 n; /* number of regs */ - __u64 reg[]; + __DECLARE_FLEX_ARRAY(__u64, reg); }; struct kvm_one_reg { @@ -2211,7 +2212,7 @@ 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