* [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug
@ 2026-02-10 7:25 Leesoo Ahn
2026-02-20 8:03 ` Leesoo Ahn
2026-02-20 17:15 ` Sean Christopherson
0 siblings, 2 replies; 3+ messages in thread
From: Leesoo Ahn @ 2026-02-10 7:25 UTC (permalink / raw)
To: lsahn; +Cc: Paolo Bonzini, open list:KERNEL VIRTUAL MACHINE (KVM), open list
Switch to using memdup_user to allocate its memory because the size of
kvm_guest_debug is over 512 bytes on Arm64 and is burdened allocation
from kernel stack.
Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>
---
virt/kvm/kvm_main.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5b5b69c97665..bc0a53129df7 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -4592,12 +4592,15 @@ static long kvm_vcpu_ioctl(struct file *filp,
break;
}
case KVM_SET_GUEST_DEBUG: {
- struct kvm_guest_debug dbg;
+ struct kvm_guest_debug *dbg;
- r = -EFAULT;
- if (copy_from_user(&dbg, argp, sizeof(dbg)))
+ dbg = memdup_user(argp, sizeof(*dbg));
+ if (IS_ERR(dbg)) {
+ r = PTR_ERR(dbg);
goto out;
- r = kvm_arch_vcpu_ioctl_set_guest_debug(vcpu, &dbg);
+ }
+ r = kvm_arch_vcpu_ioctl_set_guest_debug(vcpu, dbg);
+ kfree(dbg);
break;
}
case KVM_SET_SIGNAL_MASK: {
--
2.51.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug
2026-02-10 7:25 [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug Leesoo Ahn
@ 2026-02-20 8:03 ` Leesoo Ahn
2026-02-20 17:15 ` Sean Christopherson
1 sibling, 0 replies; 3+ messages in thread
From: Leesoo Ahn @ 2026-02-20 8:03 UTC (permalink / raw)
To: Paolo Bonzini, open list:KERNEL VIRTUAL MACHINE (KVM), open list; +Cc: lsahn
Bump up the patch in order to remind again.
2026년 2월 10일 (화) PM 4:25, Leesoo Ahn <lsahn@ooseel.net>님이 작성:
>
> Switch to using memdup_user to allocate its memory because the size of
> kvm_guest_debug is over 512 bytes on Arm64 and is burdened allocation
> from kernel stack.
>
> Signed-off-by: Leesoo Ahn <lsahn@ooseel.net>
> ---
> virt/kvm/kvm_main.c | 11 +++++++----
> 1 file changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 5b5b69c97665..bc0a53129df7 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -4592,12 +4592,15 @@ static long kvm_vcpu_ioctl(struct file *filp,
> break;
> }
> case KVM_SET_GUEST_DEBUG: {
> - struct kvm_guest_debug dbg;
> + struct kvm_guest_debug *dbg;
>
> - r = -EFAULT;
> - if (copy_from_user(&dbg, argp, sizeof(dbg)))
> + dbg = memdup_user(argp, sizeof(*dbg));
> + if (IS_ERR(dbg)) {
> + r = PTR_ERR(dbg);
> goto out;
> - r = kvm_arch_vcpu_ioctl_set_guest_debug(vcpu, &dbg);
> + }
> + r = kvm_arch_vcpu_ioctl_set_guest_debug(vcpu, dbg);
> + kfree(dbg);
> break;
> }
> case KVM_SET_SIGNAL_MASK: {
> --
> 2.51.0
>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug
2026-02-10 7:25 [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug Leesoo Ahn
2026-02-20 8:03 ` Leesoo Ahn
@ 2026-02-20 17:15 ` Sean Christopherson
1 sibling, 0 replies; 3+ messages in thread
From: Sean Christopherson @ 2026-02-20 17:15 UTC (permalink / raw)
To: Leesoo Ahn
Cc: Paolo Bonzini, open list:KERNEL VIRTUAL MACHINE (KVM), open list
On Tue, Feb 10, 2026, Leesoo Ahn wrote:
> Switch to using memdup_user to allocate its memory because the size of
> kvm_guest_debug is over 512 bytes on Arm64 and is burdened allocation
> from kernel stack.
520 bytes is a lot, but it's not _that_ much, especially since
kvm_arch_vcpu_ioctl_set_guest_debug() is leaf function (ignoring tracing).
Is there an actual problem on arm64? I.e. does this one particular allocation
lead to stack overflows that otherwise don't happen in KVM?
^ permalink raw reply [flat|nested] 3+ messages in thread
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2026-02-10 7:25 [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug Leesoo Ahn
2026-02-20 8:03 ` Leesoo Ahn
2026-02-20 17:15 ` Sean Christopherson
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