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| author | Mathias Krause <minipli@grsecurity.net> | 2024-06-14 22:28:55 +0200 |
|---|---|---|
| committer | Sean Christopherson <seanjc@google.com> | 2024-06-18 08:59:16 -0700 |
| commit | 8b8e57e5096e47ca842c100c25667195017014ae (patch) | |
| tree | e6afca8ecb2dcc66077d00a99a7c539c6efbca70 /virt | |
| parent | 5c1f50ab7fcb4e77a0b4ce102cfb890eef1ed8f1 (diff) | |
| download | lwn-8b8e57e5096e47ca842c100c25667195017014ae.tar.gz lwn-8b8e57e5096e47ca842c100c25667195017014ae.zip | |
KVM: Reject overly excessive IDs in KVM_CREATE_VCPU
If, on a 64 bit system, a vCPU ID is provided that has the upper 32 bits
set to a non-zero value, it may get accepted if the truncated to 32 bits
integer value is below KVM_MAX_VCPU_IDS and 'max_vcpus'. This feels very
wrong and triggered the reporting logic of PaX's SIZE_OVERFLOW plugin.
Instead of silently truncating and accepting such values, pass the full
value to kvm_vm_ioctl_create_vcpu() and make the existing limit checks
return an error.
Even if this is a userland ABI breaking change, no sane userland could
have ever relied on that behaviour.
Reported-by: PaX's SIZE_OVERFLOW plugin running on grsecurity's syzkaller
Fixes: 6aa8b732ca01 ("[PATCH] kvm: userspace interface")
Cc: Emese Revfy <re.emese@gmail.com>
Cc: PaX Team <pageexec@freemail.hu>
Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20240614202859.3597745-2-minipli@grsecurity.net
[sean: tweak comment about INT_MAX assertion]
Signed-off-by: Sean Christopherson <seanjc@google.com>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 436ca41f61e5..fed80bfbe99b 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -4207,12 +4207,21 @@ static void kvm_create_vcpu_debugfs(struct kvm_vcpu *vcpu) /* * Creates some virtual cpus. Good luck creating more than one. */ -static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) +static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, unsigned long id) { int r; struct kvm_vcpu *vcpu; struct page *page; + /* + * KVM tracks vCPU IDs as 'int', be kind to userspace and reject + * too-large values instead of silently truncating. + * + * Ensure KVM_MAX_VCPU_IDS isn't pushed above INT_MAX without first + * changing the storage type (at the very least, IDs should be tracked + * as unsigned ints). + */ + BUILD_BUG_ON(KVM_MAX_VCPU_IDS > INT_MAX); if (id >= KVM_MAX_VCPU_IDS) return -EINVAL; |