Commit 2619da73 authored by David Woodhouse's avatar David Woodhouse Committed by Sean Christopherson
Browse files

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



Commit 94dfc73e ("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: 94dfc73e ("treewide: uapi: Replace zero-length arrays with flexible-array members")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarDavid Woodhouse <dwmw@amazon.co.uk>
Link: https://patch.msgid.link/3abaf6aefd6e5efeff3b860ac38421d9dec908db.camel@infradead.org


[sean: tag for stable@]
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent d2ea4ff1

arch/x86/include/uapi/asm/kvm.h

+6 −6
Original line number Diff line number Diff line
@@ -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

include/uapi/linux/kvm.h

+6 −5
Original line number Diff line number Diff line
@@ -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

};