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While fuzzing KVM on RISC-V, a use-after-free was observed in
kvm_riscv_gstage_get_leaf(), where ptep_get() dereferences a
freed gstage page table page during gfn unmap.
The crash manifests as:
use-after-free in ptep_get include/linux/pgtable.h:340 [inline]
use-after-free in kvm_riscv_gstage_get_leaf arch/riscv/kvm/gstage.c:89
Call Trace:
ptep_get include/linux/pgtable.h:340 [inline]
kvm_riscv_gstage_get_leaf+0x2ea/0x358 arch/riscv/kvm/gstage.c:89
kvm_riscv_gstage_unmap_range+0xf0/0x308 arch/riscv/kvm/gstage.c:265
kvm_unmap_gfn_range+0x168/0x1fc arch/riscv/kvm/mmu.c:256
kvm_mmu_unmap_gfn_range virt/kvm/kvm_main.c:724 [inline]
page last free pid 808 tgid 808 stack trace:
kvm_riscv_mmu_free_pgd+0x1b6/0x26a arch/riscv/kvm/mmu.c:457
kvm_arch_flush_shadow_all+0x1a/0x24 arch/riscv/kvm/mmu.c:134
kvm_flush_shadow_all virt/kvm/kvm_main.c:344 [inline]
The UAF is caused by gstage page table walks running concurrently with
gstage pgd teardown. In particular, kvm_unmap_gfn_range() can traverse
gstage page tables while kvm_arch_flush_shadow_all() frees the pgd,
leading to use-after-free of page table pages.
Fix the issue by serializing gstage unmap and pgd teardown with
kvm->mmu_lock. Holding mmu_lock ensures that gstage page tables
remain valid for the duration of unmap operations and prevents
concurrent frees.
This matches existing RISC-V KVM usage of mmu_lock to protect gstage
map/unmap operations, e.g. kvm_riscv_mmu_iounmap.
Fixes:
|
||
|---|---|---|
| .. | ||
| boot | ||
| configs | ||
| crypto | ||
| errata | ||
| include | ||
| kernel | ||
| kvm | ||
| lib | ||
| mm | ||
| net | ||
| purgatory | ||
| tools | ||
| Kbuild | ||
| Kconfig | ||
| Kconfig.debug | ||
| Kconfig.errata | ||
| Kconfig.socs | ||
| Kconfig.vendor | ||
| Makefile | ||
| Makefile.postlink | ||