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KVM: x86: Use __DECLARE_FLEX_ARRAY() for UAPI structures with VLAs

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Commit 94dfc73e7c ("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: 94dfc73e7c ("treewide: uapi: Replace zero-length arrays with flexible-array members")
Cc: stable@vger.kernel.org
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/3abaf6aefd6e5efeff3b860ac38421d9dec908db.camel@infradead.org
[sean: tag for stable@]
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
David Woodhouse
2026-03-05 20:49:55 +01:00
committed by Sean Christopherson
parent d2ea4ff1ce
commit 2619da73bb
2 changed files with 12 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
arch/x86/include/uapi/asm/kvm.h
View File

@@ -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
@@ -566,7 +566,7 @@ 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

11
include/uapi/linux/kvm.h
View File

@@ -11,6 +11,7 @@
#include <linux/const.h>
#include <linux/types.h>
#include <linux/compiler.h>
#include <linux/stddef.h>
#include <linux/ioctl.h>
#include <asm/kvm.h>
@@ -542,7 +543,7 @@ 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 \
@@ -592,7 +593,7 @@ 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 */
@@ -1051,7 +1052,7 @@ 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)
@@ -1142,7 +1143,7 @@ struct kvm_dirty_tlb {
struct kvm_reg_list {
__u64 n; /* number of regs */
__u64 reg[];
__DECLARE_FLEX_ARRAY(__u64, reg);
};
struct kvm_one_reg {
@@ -1608,7 +1609,7 @@ struct kvm_stats_desc {
#ifdef __KERNEL__
char name[KVM_STATS_NAME_SIZE];
#else
char name[];
__DECLARE_FLEX_ARRAY(char, name);
#endif
};