From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 005794EC65A; Tue, 13 Oct 2026 12:16:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893763; cv=none; b=gseXr3mSRSTuTI5nYGJKP0b5KXhpqE2zlgbRsKJdxQym4RuluuxRuz2sEolLjKdoj0FfmVTx6uuaCunLxrZdmzaG8XCK7EmaAnv2+Z2Yqn3YqqgQd92UcSDH9B/s894LgcPIBYiYo4xvSjxCgXiDlDRZtLJzMvEsZhCyoAxxxKw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791893763; c=relaxed/simple; bh=T1aXq5SwTzxVcvFp6v6wjLJYTa3NJVCUb2ziFLFwaXo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ItO1mgIrIc1ZPtxYCIU106GeoW6OtfcBssVmDf0p9nLSUVyOd377hBSFrOLRw6nfECyLx6XuF0HrRYQRMoC3hY68p9Htjk28Yyiu0mktog3G/ifduzcYj96WUkCj7NKyFiKuQ1lrVmHRvFiMDugNrLqd1djgjo/yKcYNz4Znm48= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=LymFJfFC; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="LymFJfFC" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 48B1D1F000FF; Tue, 13 Oct 2026 12:16:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791893761; bh=9fcQTwUztA4RihxmniRBFr/59x3a+EUzlcfL9u/epbo=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=LymFJfFCO7KsI0qrtRkHN5KCJa2kb11l6rCAJ26eByeI/fH+Oyx/B+1OsXr7g71iR 0FYqZAiAR1HHGL1+QQ1mHfwwMZxWr/Qowm7/dUOyUETl0obPECziijflErC0YCNNpZ sWVcS21dORR7Vxbu/7Pb6GeSquChyT/AHpm/KO4w= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Carlos=20L=C3=B3pez?= , Marc Zyngier , Sasha Levin Subject: [PATCH 6.18 333/621] KVM: arm64: vgic: Fix race between LPI release and re-registration Date: Tue, 13 Oct 2026 13:35:28 +0200 Message-ID: <20261013112928.755134912@linuxfoundation.org> X-Mailer: git-send-email 2.56.0 In-Reply-To: <20261013112920.855194808@linuxfoundation.org> References: <20261013112920.855194808@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Carlos López [ Upstream commit cbfe2b24a1ea9de35032dbdd100fdc700f5be92d ] Fix a potential race between decrementing an LPI's reference count and evicting that structure from the LPI xarray. LPI structures are maintained in the VGIC LPI xarray (dist->lpi_xa). When the reference count of an LPI structure drops to zero, vgic_release_lpi_locked() removes the structure from the xarray and frees it under the xarray lock. However, the release of an LPI can race with a concurrent LPI re-registration with the same INTID via vgic_add_lpi() on another CPU, since the reference count drop and the xarray eviction are not performed in a single atomic step. This can happen e.g. if the guest issues a DISCARD while the LPI is still referenced from a vCPU's active-pending list (ap_list), and the same INTID is re-mapped via MAPTI. Particularly, vgic_release_lpi_locked() is called from two distinct paths: direct release via vgic_put_irq(), and deferred release via vgic_release_deleted_lpis(). During direct release, the issue can result in deleting a newly registered LPI from the xarray: CPU0 (Releasing LPI) CPU1 (Adding new LPI) ==================== ===================== vgic_put_irq() __vgic_put_irq() refcount_dec_and_test() vgic_add_lpi() xa_lock_irqsave() old_irq = xa_load(.., intid) vgic_try_get_irq_ref(old_irq) == false new IRQ inserted --> __xa_store(.., intid, ..) xa_unlock_irqrestore() xa_lock_irqsave(); vgic_release_lpi_locked() __xa_erase(.., irq->intid) <-- BUG: new IRQ is erased kfree_rcu(old_irq) During the deferred release path, the old IRQ can be leaked: CPU0 (Releasing LPI) CPU1 (Adding new LPI) ==================== ===================== vgic_put_irq_norelease() __vgic_put_irq() refcount_dec_and_test() irq->pending_release = true vgic_add_lpi() xa_lock_irqsave() old_irq = xa_load(.., intid) vgic_try_get_irq_ref(oldirq) == false BUG: old IRQ overwritten --> __xa_store(.., intid, ..) xa_unlock_irqrestore() vgic_release_deleted_lpis() xa_lock_irqsave() xa_for_each() { .. } <-- old IRQ with pending_release = true is gone, so it cannot be released To fix the direct release path, move the reference count drop inside the xarray lock, making sure that vgic_add_lpi() never encounters the to-be-released LPI. In the deferred release path, the refcount drop must happen under a raw spinlock, so the xarray lock cannot be grabbed, and the same solution does not work. Instead, update vgic_add_lpi(), so that if it evicts an LPI from the xarray, it takes on the responsibility of freeing it. Consequently, an LPI may now be freed concurrently after a deferred release drops the refcount, so accessing the pending_release field is no longer safe from use-after-free. Delete all uses of the flag, and update vgic_release_deleted_lpis() to identify orphaned LPIs purely based on their refcount. Reported-by: Claude:claude-opus-4-6 Fixes: 3a08a6ca7c37 ("KVM: arm64: vgic-v3: Use bare refcount for VGIC LPIs") Fixes: d54594accf73 ("KVM: arm64: vgic-v3: Erase LPIs from xarray outside of raw spinlocks") Signed-off-by: Carlos López Link: https://patch.msgid.link/20260715105137.3973823-4-clopez@suse.de Signed-off-by: Marc Zyngier Signed-off-by: Sasha Levin --- arch/arm64/kvm/vgic/vgic-its.c | 24 ++++++++++++++++-------- arch/arm64/kvm/vgic/vgic.c | 18 ++++++++---------- include/kvm/arm_vgic.h | 3 --- 3 files changed, 24 insertions(+), 21 deletions(-) diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c index e3c182352ffca..7ce07c8eb5b7e 100644 --- a/arch/arm64/kvm/vgic/vgic-its.c +++ b/arch/arm64/kvm/vgic/vgic-its.c @@ -116,18 +116,26 @@ static struct vgic_irq *vgic_add_lpi(struct kvm *kvm, u32 intid, kfree(irq); irq = oldirq; } else { - ret = xa_err(__xa_store(&dist->lpi_xa, intid, irq, 0)); - } - - xa_unlock_irqrestore(&dist->lpi_xa, flags); + /* + * The entry is either empty or contains a dead LPI (refcount=0) + * from the deferred release path, pending cleanup by + * vgic_release_deleted_lpis(). Evict and free it if present. + */ + oldirq = __xa_store(&dist->lpi_xa, intid, irq, 0); + ret = xa_err(oldirq); + if (ret) { + xa_unlock_irqrestore(&dist->lpi_xa, flags); + kfree(irq); - if (ret) { - xa_release(&dist->lpi_xa, intid); - kfree(irq); + return ERR_PTR(ret); + } - return ERR_PTR(ret); + if (oldirq && !WARN_ON_ONCE(refcount_read(&oldirq->refcount))) + kfree_rcu(oldirq, rcu); } + xa_unlock_irqrestore(&dist->lpi_xa, flags); + /* * We "cache" the configuration table entries in our struct vgic_irq's. * However we only have those structs for mapped IRQs, so we read in diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c index 5ba673289ef43..7c8ec44824157 100644 --- a/arch/arm64/kvm/vgic/vgic.c +++ b/arch/arm64/kvm/vgic/vgic.c @@ -131,11 +131,7 @@ static __must_check bool __vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq) static __must_check bool vgic_put_irq_norelease(struct kvm *kvm, struct vgic_irq *irq) { - if (!__vgic_put_irq(kvm, irq)) - return false; - - irq->pending_release = true; - return true; + return __vgic_put_irq(kvm, irq); } void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq) @@ -152,12 +148,14 @@ void vgic_put_irq(struct kvm *kvm, struct vgic_irq *irq) guard(spinlock_irqsave)(&dist->lpi_xa.xa_lock); } - if (!__vgic_put_irq(kvm, irq)) + if (irq->intid < VGIC_MIN_LPI) return; - xa_lock_irqsave(&dist->lpi_xa, flags); - vgic_release_lpi_locked(dist, irq); - xa_unlock_irqrestore(&dist->lpi_xa, flags); + if (refcount_dec_and_lock_irqsave(&irq->refcount, + &dist->lpi_xa.xa_lock, &flags)) { + vgic_release_lpi_locked(dist, irq); + xa_unlock_irqrestore(&dist->lpi_xa, flags); + } } static void vgic_release_deleted_lpis(struct kvm *kvm) @@ -169,7 +167,7 @@ static void vgic_release_deleted_lpis(struct kvm *kvm) xa_lock_irqsave(&dist->lpi_xa, flags); xa_for_each(&dist->lpi_xa, intid, irq) { - if (irq->pending_release) + if (!refcount_read(&irq->refcount)) vgic_release_lpi_locked(dist, irq); } diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h index 7a0b972eb1b12..25eb6ba9dd23c 100644 --- a/include/kvm/arm_vgic.h +++ b/include/kvm/arm_vgic.h @@ -140,9 +140,6 @@ struct vgic_irq { * the pending state for both level * and edge triggered IRQs. */ bool active; - bool pending_release; /* Used for LPIs only, unreferenced IRQ - * pending a release */ - bool enabled; bool hw; /* Tied to HW IRQ */ refcount_t refcount; /* Used for LPIs */ -- 2.53.0