linux-kernel - [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest

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Message-ID: <20260210072530.918038-1-lsahn@ooseel.net>
Date: Tue, 10 Feb 2026 16:25:30 +0900
From: Leesoo Ahn <lsahn@...eel.net>
To: lsahn@...eel.net
Cc: Paolo Bonzini <pbonzini@...hat.com>,
	kvm@...r.kernel.org (open list:KERNEL VIRTUAL MACHINE (KVM)),
	linux-kernel@...r.kernel.org (open list)
Subject: [PATCH v1] KVM: Use memdup_user instead of kernel stack to allocate kvm_guest_debug

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@...eel.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