[PATCH kernel] KVM: PPC: Protect memslots while validating user address

[PATCH kernel] KVM: PPC: Protect memslots while validating user address

[Alexey Kardashevskiy]

Guest physical to user address translation uses KVM memslots and reading
these requires holding the kvm->srcu lock. However recently introduced
kvmppc_tce_validate() broke the rule (see the lockdep warning below).

This moves srcu_read_lock(&vcpu->kvm->srcu) earlier to protect
kvmppc_tce_validate() as well.

==============WARNING: suspicious RCU usage
5.1.0-rc2-le_nv2_aikATfstn1-p1 #380 Not tainted
-----------------------------
include/linux/kvm_host.h:605 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by qemu-system-ppc/8020:
 #0: 0000000094972fe9 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0xdc/0x850 [kvm]

stack backtrace:
CPU: 44 PID: 8020 Comm: qemu-system-ppc Not tainted 5.1.0-rc2-le_nv2_aikATfstn1-p1 #380
Call Trace:
[c000003fece8f740] [c000000000bcc134] dump_stack+0xe8/0x164 (unreliable)
[c000003fece8f790] [c000000000181be0] lockdep_rcu_suspicious+0x130/0x170
[c000003fece8f810] [c0000000000d5f50] kvmppc_tce_to_ua+0x280/0x290
[c000003fece8f870] [c00800001a7e2c78] kvmppc_tce_validate+0x80/0x1b0 [kvm]
[c000003fece8f8e0] [c00800001a7e3fac] kvmppc_h_put_tce+0x94/0x3e4 [kvm]
[c000003fece8f9a0] [c00800001a8baac4] kvmppc_pseries_do_hcall+0x30c/0xce0 [kvm_hv]
[c000003fece8fa10] [c00800001a8bd89c] kvmppc_vcpu_run_hv+0x694/0xec0 [kvm_hv]
[c000003fece8fae0] [c00800001a7d95dc] kvmppc_vcpu_run+0x34/0x48 [kvm]
[c000003fece8fb00] [c00800001a7d56bc] kvm_arch_vcpu_ioctl_run+0x2f4/0x400 [kvm]
[c000003fece8fb90] [c00800001a7c3618] kvm_vcpu_ioctl+0x460/0x850 [kvm]
[c000003fece8fd00] [c00000000041c4f4] do_vfs_ioctl+0xe4/0x930
[c000003fece8fdb0] [c00000000041ce04] ksys_ioctl+0xc4/0x110
[c000003fece8fe00] [c00000000041ce78] sys_ioctl+0x28/0x80
[c000003fece8fe20] [c00000000000b5a4] system_call+0x5c/0x70

Fixes: 42de7b9e2167 ("KVM: PPC: Validate TCEs against preregistered memory page sizes", 2018-09-10)
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 arch/powerpc/kvm/book3s_64_vio.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index f02b04973710..f100e331e69b 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -543,14 +543,14 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
 	if (ret != H_SUCCESS)
 		return ret;
 
+	idx = srcu_read_lock(&vcpu->kvm->srcu);
+
 	ret = kvmppc_tce_validate(stt, tce);
 	if (ret != H_SUCCESS)
-		return ret;
+		goto unlock_exit;
 
 	dir = iommu_tce_direction(tce);
 
-	idx = srcu_read_lock(&vcpu->kvm->srcu);
-
 	if ((dir != DMA_NONE) && kvmppc_tce_to_ua(vcpu->kvm, tce, &ua, NULL)) {
 		ret = H_PARAMETER;
 		goto unlock_exit;
-- 
2.17.1

Re: [PATCH kernel] KVM: PPC: Protect memslots while validating user address

[Paul Mackerras]

On Fri, Mar 29, 2019 at 04:41:13PM +1100, Alexey Kardashevskiy wrote:
> Guest physical to user address translation uses KVM memslots and reading
> these requires holding the kvm->srcu lock. However recently introduced
> kvmppc_tce_validate() broke the rule (see the lockdep warning below).
> 
> This moves srcu_read_lock(&vcpu->kvm->srcu) earlier to protect
> kvmppc_tce_validate() as well.
> 
> ==============> WARNING: suspicious RCU usage
> 5.1.0-rc2-le_nv2_aikATfstn1-p1 #380 Not tainted
> -----------------------------
> include/linux/kvm_host.h:605 suspicious rcu_dereference_check() usage!
> 
> other info that might help us debug this:
> 
> 
> rcu_scheduler_active = 2, debug_locks = 1
> 1 lock held by qemu-system-ppc/8020:
>  #0: 0000000094972fe9 (&vcpu->mutex){+.+.}, at: kvm_vcpu_ioctl+0xdc/0x850 [kvm]
> 
> stack backtrace:
> CPU: 44 PID: 8020 Comm: qemu-system-ppc Not tainted 5.1.0-rc2-le_nv2_aikATfstn1-p1 #380
> Call Trace:
> [c000003fece8f740] [c000000000bcc134] dump_stack+0xe8/0x164 (unreliable)
> [c000003fece8f790] [c000000000181be0] lockdep_rcu_suspicious+0x130/0x170
> [c000003fece8f810] [c0000000000d5f50] kvmppc_tce_to_ua+0x280/0x290
> [c000003fece8f870] [c00800001a7e2c78] kvmppc_tce_validate+0x80/0x1b0 [kvm]
> [c000003fece8f8e0] [c00800001a7e3fac] kvmppc_h_put_tce+0x94/0x3e4 [kvm]
> [c000003fece8f9a0] [c00800001a8baac4] kvmppc_pseries_do_hcall+0x30c/0xce0 [kvm_hv]
> [c000003fece8fa10] [c00800001a8bd89c] kvmppc_vcpu_run_hv+0x694/0xec0 [kvm_hv]
> [c000003fece8fae0] [c00800001a7d95dc] kvmppc_vcpu_run+0x34/0x48 [kvm]
> [c000003fece8fb00] [c00800001a7d56bc] kvm_arch_vcpu_ioctl_run+0x2f4/0x400 [kvm]
> [c000003fece8fb90] [c00800001a7c3618] kvm_vcpu_ioctl+0x460/0x850 [kvm]
> [c000003fece8fd00] [c00000000041c4f4] do_vfs_ioctl+0xe4/0x930
> [c000003fece8fdb0] [c00000000041ce04] ksys_ioctl+0xc4/0x110
> [c000003fece8fe00] [c00000000041ce78] sys_ioctl+0x28/0x80
> [c000003fece8fe20] [c00000000000b5a4] system_call+0x5c/0x70
> 
> Fixes: 42de7b9e2167 ("KVM: PPC: Validate TCEs against preregistered memory page sizes", 2018-09-10)
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Thanks, patch applied to my kvm-ppc-fixes tree.

Paul.