With PR KVM, shutting down a VM causes the host kernel to crash:
[ 314.219284] BUG: Unable to handle kernel data access on read at
0xc00800000176c638
[ 314.219299] Faulting instruction address: 0xc008000000d4ddb0
cpu 0x0: Vector: 300 (Data Access) at [c00000036da077a0]
pc: c008000000d4ddb0: kvmppc_mmu_pte_flush_all+0x68/0xd0 [kvm_pr]
lr: c008000000d4dd94: kvmppc_mmu_pte_flush_all+0x4c/0xd0 [kvm_pr]
sp: c00000036da07a30
msr: 900000010280b033
dar: c00800000176c638
dsisr: 40000000
current = 0xc00000036d4c0000
paca = 0xc000000001a00000 irqmask: 0x03 irq_happened: 0x01
pid = 1992, comm = qemu-system-ppc
Linux version 5.6.0-master-gku+ (greg@palmb) (gcc version 7.5.0 (Ubuntu
7.5.0-3ubuntu1~18.04)) #17 SMP Wed Mar 18 13:49:29 CET 2020
enter ? for help
[c00000036da07ab0] c008000000d4fbe0 kvmppc_mmu_destroy_pr+0x28/0x60 [kvm_pr]
[c00000036da07ae0] c0080000009eab8c kvmppc_mmu_destroy+0x34/0x50 [kvm]
[c00000036da07b00] c0080000009e50c0 kvm_arch_vcpu_destroy+0x108/0x140 [kvm]
[c00000036da07b30] c0080000009d1b50 kvm_vcpu_destroy+0x28/0x80 [kvm]
[c00000036da07b60] c0080000009e4434 kvm_arch_destroy_vm+0xbc/0x190 [kvm]
[c00000036da07ba0] c0080000009d9c2c kvm_put_kvm+0x1d4/0x3f0 [kvm]
[c00000036da07c00] c0080000009da760 kvm_vm_release+0x38/0x60 [kvm]
[c00000036da07c30] c000000000420be0 __fput+0xe0/0x310
[c00000036da07c90] c0000000001747a0 task_work_run+0x150/0x1c0
[c00000036da07cf0] c00000000014896c do_exit+0x44c/0xd00
[c00000036da07dc0] c0000000001492f4 do_group_exit+0x64/0xd0
[c00000036da07e00] c000000000149384 sys_exit_group+0x24/0x30
[c00000036da07e20] c00000000000b9d0 system_call+0x5c/0x68
This is caused by a use-after-free in kvmppc_mmu_pte_flush_all()
which dereferences vcpu->arch.book3s which was previously freed by
kvmppc_core_vcpu_free_pr(). This happens because kvmppc_mmu_destroy()
is called after kvmppc_core_vcpu_free() since commit ff030fdf5573
("KVM: PPC: Move kvm_vcpu_init() invocation to common code").
The kvmppc_mmu_destroy() helper calls one of the following depending
on the KVM backend:
- kvmppc_mmu_destroy_hv() which does nothing (Book3s HV)
- kvmppc_mmu_destroy_pr() which undoes the effects of
kvmppc_mmu_init() (Book3s PR 32-bit)
- kvmppc_mmu_destroy_pr() which undoes the effects of
kvmppc_mmu_init() (Book3s PR 64-bit)
- kvmppc_mmu_destroy_e500() which does nothing (BookE e500/e500mc)
It turns out that this is only relevant to PR KVM actually. And both
32 and 64 backends need vcpu->arch.book3s to be valid when calling
kvmppc_mmu_destroy_pr(). So instead of calling kvmppc_mmu_destroy()
from kvm_arch_vcpu_destroy(), call kvmppc_mmu_destroy_pr() at the
beginning of kvmppc_core_vcpu_free_pr(). This is consistent with
kvmppc_mmu_init() being the last call in kvmppc_core_vcpu_create_pr().
For the same reason, if kvmppc_core_vcpu_create_pr() returns an
error then this means that kvmppc_mmu_init() was either not called
or failed, in which case kvmppc_mmu_destroy() should not be called.
Drop the line in the error path of kvm_arch_vcpu_create().
Fixes: ff030fdf5573 ("KVM: PPC: Move kvm_vcpu_init() invocation to common code")
Signed-off-by: Greg Kurz <gr...@kaod.org>
---
arch/powerpc/kvm/book3s_pr.c | 1 +
arch/powerpc/kvm/powerpc.c | 2 --
2 files changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_pr.c b/arch/powerpc/kvm/book3s_pr.c
index 729a0f12a752..db3a87319642 100644
--- a/arch/powerpc/kvm/book3s_pr.c
+++ b/arch/powerpc/kvm/book3s_pr.c
@@ -1817,6 +1817,7 @@ static void kvmppc_core_vcpu_free_pr(struct kvm_vcpu
*vcpu)
{
struct kvmppc_vcpu_book3s *vcpu_book3s = to_book3s(vcpu);
+ kvmppc_mmu_destroy_pr(vcpu);
free_page((unsigned long)vcpu->arch.shared & PAGE_MASK);
#ifdef CONFIG_KVM_BOOK3S_32_HANDLER
kfree(vcpu->arch.shadow_vcpu);
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index 1af96fb5dc6f..302e9dccdd6d 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -759,7 +759,6 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
return 0;
out_vcpu_uninit:
- kvmppc_mmu_destroy(vcpu);
kvmppc_subarch_vcpu_uninit(vcpu);
return err;
}
@@ -792,7 +791,6 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
kvmppc_core_vcpu_free(vcpu);
- kvmppc_mmu_destroy(vcpu);
kvmppc_subarch_vcpu_uninit(vcpu);
}
