From: Sean Christopherson <seanjc@google.com> stable inclusion from stable-v6.6.130 commit ec3be7dc9391085a2d96700e159d66d1328b7ff6 category: bugfix bugzilla: https://atomgit.com/src-openeuler/kernel/issues/14809 CVE: CVE-2026-43265 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- [ Upstream commit ead63640d4e72e6f6d464f4e31f7fecb79af8869 ] Ignore -EBUSY when checking nested events after exiting a blocking state while L2 is active, as exiting to userspace will generate a spurious userspace exit, usually with KVM_EXIT_UNKNOWN, and likely lead to the VM's demise. Continuing with the wakeup isn't perfect either, as *something* has gone sideways if a vCPU is awakened in L2 with an injected event (or worse, a nested run pending), but continuing on gives the VM a decent chance of surviving without any major side effects. As explained in the Fixes commits, it _should_ be impossible for a vCPU to be put into a blocking state with an already-injected event (exception, IRQ, or NMI). Unfortunately, userspace can stuff MP_STATE and/or injected events, and thus put the vCPU into what should be an impossible state. Don't bother trying to preserve the WARN, e.g. with an anti-syzkaller Kconfig, as WARNs can (hopefully) be added in paths where _KVM_ would be violating x86 architecture, e.g. by WARNing if KVM attempts to inject an exception or interrupt while the vCPU isn't running. Cc: Alessandro Ratti <alessandro@0x65c.net> Cc: stable@vger.kernel.org Fixes: 26844fee6ade ("KVM: x86: never write to memory from kvm_vcpu_check_block()") Fixes: 45405155d876 ("KVM: x86: WARN if a vCPU gets a valid wakeup that KVM can't yet inject") Link: https://syzkaller.appspot.com/text?tag=ReproC&x=10d4261a580000 Reported-by: syzbot+1522459a74d26b0ac33a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/671bc7a7.050a0220.455e8.022a.GAE@google.com Link: https://patch.msgid.link/20260109030657.994759-1-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Sasha Levin <sashal@kernel.org> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com> --- arch/x86/kvm/x86.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 8464796e4cdc..6ca2798494dd 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11202,8 +11202,7 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu) if (is_guest_mode(vcpu)) { int r = kvm_check_nested_events(vcpu); - WARN_ON_ONCE(r == -EBUSY); - if (r < 0) + if (r < 0 && r != -EBUSY) return 0; } -- 2.34.1