In the Linux kernel, the following vulnerability has been resolved: KVM: PPC: Book3S HV: fix…

Why it is Amber

• CVSS 8.8 high
• On your watchlist: linux kernel

References

• https://git.kernel.org/stable/c/24b634852413229bb8340d908b115c3365f3a247
• https://git.kernel.org/stable/c/4d8f7b1f586375df8bce23a0909566ad5e852259
• https://git.kernel.org/stable/c/51938dfa8a51a4f85328413fca9b6e21f9d2d088
• https://git.kernel.org/stable/c/e37fba1ba69385cff2d0e60b371ee19e7d1852d1
• https://git.kernel.org/stable/c/ec2d7a52b3996ae81131617b4afc0af31583c1b4
• https://git.kernel.org/stable/c/fbf69b7d0555ee83c871f58750770f74b7179ad1

Original description

In the Linux kernel, the following vulnerability has been resolved: KVM: PPC: Book3S HV: fix use-after-free in kvmhv_emulate_tlbie_all_lpid() kvmhv_emulate_tlbie_all_lpid() iterates the nested-guest IDR and drops mmu_lock before calling kvmhv_emulate_tlbie_lpid(), but does not hold a reference on the kvm_nested_guest pointer obtained from the IDR. A concurrent vCPU issuing a single-LPID tlbie (is=2, ric=2) can race through kvmhv_flush_nested() -> kvmhv_remove_nested() -> idr_remove / --refcnt -> kvmhv_release_nested() -> kfree(gp) in that window, leaving the iterating vCPU with a dangling pointer. The subsequent mutex_lock(&gp->tlb_lock) and accesses to gp->shadow_pgtable, gp->shadow_lpid and gp->l1_host all touch freed memory. The free path is fully L1-controlled. Fix this by incrementing gp->refcnt inside the loop before dropping mmu_lock, mirroring what kvmhv_get_nested() does, and releasing the reference with kvmhv_put_nested() after the per-guest work completes. This is the same get/put discipline already used at every other call site that drops mmu_lock while holding a nested-guest pointer.