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Wed, 15 Jul 2026 10:59:23 +0000 From: =?UTF-8?q?Carlos=20L=C3=B3pez?= To: kvmarm@lists.linux.dev, linux-kernel@vger.kernel.org Cc: maz@kernel.org, oupton@kernel.org, joey.gouly@arm.com, seiden@linux.ibm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com, catalin.marinas@arm.com, will@kernel.org, linux-arm-kernel@lists.infradead.org, =?UTF-8?q?Carlos=20L=C3=B3pez?= Subject: [PATCH v6 1/2] KVM: arm64: vgic: Fix race between LPI release and re-registration Date: Wed, 15 Jul 2026 12:51:37 +0200 Message-ID: <20260715105137.3973823-4-clopez@suse.de> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260715105137.3973823-3-clopez@suse.de> References: <20260715105137.3973823-3-clopez@suse.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Queue-Id: DE39978373 X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RBL_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:104:10:150:64:97:from]; RCVD_VIA_SMTP_AUTH(0.00)[]; ARC_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; FUZZY_RATELIMITED(0.00)[rspamd.com]; RCPT_COUNT_TWELVE(0.00)[12]; RCVD_TLS_ALL(0.00)[]; DNSWL_BLOCKED(0.00)[2a07:de40:b281:106:10:150:64:167:received]; TO_DN_SOME(0.00)[]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; RECEIVED_SPAMHAUS_BLOCKED_OPENRESOLVER(0.00)[2a07:de40:b281:106:10:150:64:167:received]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:rdns,imap1.dmz-prg2.suse.org:helo,suse.de:dkim,suse.de:email,suse.de:mid]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Server: rspamd1.dmz-prg2.suse.org X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260715_035927_400876_86CB34B5 X-CRM114-Status: GOOD ( 21.99 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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 --- 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 67d107e9a77d..2240bdf20c92 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 5a4768d8cd4f..eea9db2bac4a 100644 --- a/arch/arm64/kvm/vgic/vgic.c +++ b/arch/arm64/kvm/vgic/vgic.c @@ -146,11 +146,7 @@ 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) @@ -167,12 +163,14 @@ 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_is_lpi(kvm, irq->intid)) 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) @@ -184,7 +182,7 @@ 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 fe49fb56dc3c..cefddc9c621d 100644 --- a/include/kvm/arm_vgic.h +++ b/include/kvm/arm_vgic.h @@ -247,9 +247,6 @@ struct vgic_irq { * affinity reg (v3). */ - bool pending_release:1; /* Used for LPIs only, unreferenced IRQ - * pending a release */ - bool pending_latch:1; /* The pending latch state used to calculate * the pending state for both level * and edge triggered IRQs. */ -- 2.51.0