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KVM: x86: Allocate/free user_return_msrs at kvm.ko (un)loading time

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Move user_return_msrs allocation/free from vendor modules (kvm-intel.ko and
kvm-amd.ko) (un)loading time to kvm.ko's to make it less risky to access
user_return_msrs in kvm.ko. Tying the lifetime of user_return_msrs to
vendor modules makes every access to user_return_msrs prone to
use-after-free issues as vendor modules may be unloaded at any time.

Opportunistically turn the per-CPU variable into full structs, as there's
no practical difference between statically allocating the memory and
allocating it unconditionally during module_init().

Zero out kvm_nr_uret_msrs on vendor module exit to further minimize the
chances of consuming stale data, and WARN on vendor module load if KVM
thinks there are existing user-return MSRs.

Note!  The user-return MSRs also need to be "destroyed" if
ops->hardware_setup() fails, as both SVM and VMX expect common KVM to
clean up (because common code, not vendor code, is responsible for
kvm_nr_uret_msrs).

Signed-off-by: Chao Gao <chao.gao@intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Link: https://patch.msgid.link/20251108013601.902918-1-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Chao Gao
2025-11-07 17:36:01 -08:00
committed by Sean Christopherson
parent e78fb96b41
commit 11d984633f
1 changed files with 13 additions and 27 deletions
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40
arch/x86/kvm/x86.c
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@@ -209,7 +209,7 @@ struct kvm_user_return_msrs {
u32 __read_mostly kvm_nr_uret_msrs;
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_nr_uret_msrs);
static u32 __read_mostly kvm_uret_msrs_list[KVM_MAX_NR_USER_RETURN_MSRS];
static struct kvm_user_return_msrs __percpu *user_return_msrs;
static DEFINE_PER_CPU(struct kvm_user_return_msrs, user_return_msrs);
#define KVM_SUPPORTED_XCR0 (XFEATURE_MASK_FP | XFEATURE_MASK_SSE \
| XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
@@ -572,25 +572,14 @@ static inline void kvm_async_pf_hash_reset(struct kvm_vcpu *vcpu)
vcpu->arch.apf.gfns[i] = ~0;
}
static int kvm_init_user_return_msrs(void)
{
user_return_msrs = alloc_percpu(struct kvm_user_return_msrs);
if (!user_return_msrs) {
pr_err("failed to allocate percpu user_return_msrs\n");
return -ENOMEM;
}
kvm_nr_uret_msrs = 0;
return 0;
}
static void kvm_free_user_return_msrs(void)
static void kvm_destroy_user_return_msrs(void)
{
int cpu;
for_each_possible_cpu(cpu)
WARN_ON_ONCE(per_cpu_ptr(user_return_msrs, cpu)->registered);
WARN_ON_ONCE(per_cpu(user_return_msrs, cpu).registered);
free_percpu(user_return_msrs);
kvm_nr_uret_msrs = 0;
}
static void kvm_on_user_return(struct user_return_notifier *urn)
@@ -653,7 +642,7 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_find_user_return_msr);
static void kvm_user_return_msr_cpu_online(void)
{
struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
struct kvm_user_return_msrs *msrs = this_cpu_ptr(&user_return_msrs);
u64 value;
int i;
@@ -675,7 +664,7 @@ static void kvm_user_return_register_notifier(struct kvm_user_return_msrs *msrs)
int kvm_set_user_return_msr(unsigned slot, u64 value, u64 mask)
{
struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
struct kvm_user_return_msrs *msrs = this_cpu_ptr(&user_return_msrs);
int err;
value = (value & mask) | (msrs->values[slot].host & ~mask);
@@ -693,13 +682,13 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_set_user_return_msr);
u64 kvm_get_user_return_msr(unsigned int slot)
{
return this_cpu_ptr(user_return_msrs)->values[slot].curr;
return this_cpu_ptr(&user_return_msrs)->values[slot].curr;
}
EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_get_user_return_msr);
static void drop_user_return_notifiers(void)
{
struct kvm_user_return_msrs *msrs = this_cpu_ptr(user_return_msrs);
struct kvm_user_return_msrs *msrs = this_cpu_ptr(&user_return_msrs);
if (msrs->registered)
kvm_on_user_return(&msrs->urn);
@@ -10022,13 +10011,9 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
return -ENOMEM;
}
r = kvm_init_user_return_msrs();
if (r)
goto out_free_x86_emulator_cache;
r = kvm_mmu_vendor_module_init();
if (r)
goto out_free_percpu;
goto out_free_x86_emulator_cache;
kvm_caps.supported_vm_types = BIT(KVM_X86_DEFAULT_VM);
kvm_caps.supported_mce_cap = MCG_CTL_P | MCG_SER_P;
@@ -10053,6 +10038,8 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
if (boot_cpu_has(X86_FEATURE_ARCH_CAPABILITIES))
rdmsrq(MSR_IA32_ARCH_CAPABILITIES, kvm_host.arch_capabilities);
WARN_ON_ONCE(kvm_nr_uret_msrs);
r = ops->hardware_setup();
if (r != 0)
goto out_mmu_exit;
@@ -10125,9 +10112,8 @@ out_unwind_ops:
kvm_x86_ops.enable_virtualization_cpu = NULL;
kvm_x86_call(hardware_unsetup)();
out_mmu_exit:
kvm_destroy_user_return_msrs();
kvm_mmu_vendor_module_exit();
out_free_percpu:
kvm_free_user_return_msrs();
out_free_x86_emulator_cache:
kmem_cache_destroy(x86_emulator_cache);
return r;
@@ -10155,8 +10141,8 @@ void kvm_x86_vendor_exit(void)
cancel_work_sync(&pvclock_gtod_work);
#endif
kvm_x86_call(hardware_unsetup)();
kvm_destroy_user_return_msrs();
kvm_mmu_vendor_module_exit();
kvm_free_user_return_msrs();
kmem_cache_destroy(x86_emulator_cache);
#ifdef CONFIG_KVM_XEN
static_key_deferred_flush(&kvm_xen_enabled);