CVE-2026-43265KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block()

Official description

In the Linux kernel, the following vulnerability has been resolved: KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block() 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.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/78265cd066d73a5cb41c088fcae4a2515e480d97
• https://git.kernel.org/stable/c/ec3be7dc9391085a2d96700e159d66d1328b7ff6
• https://git.kernel.org/stable/c/2657439265d34a911886b916ba8be97ecc117d51
• https://git.kernel.org/stable/c/1e88b5f854bdb469424132e0bb44793ad7a7c20a
• https://git.kernel.org/stable/c/1c957773063ed3264953597e32990a748381caf6
• https://git.kernel.org/stable/c/ead63640d4e72e6f6d464f4e31f7fecb79af8869