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Fri, 14 Aug 2026 03:00:20 -0700 (PDT) From: Zhenhao Wan Date: Fri, 14 Aug 2026 18:00:05 +0800 Subject: [PATCH v2] drm/nouveau/svm: drain fault handler before freeing svmm Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20260814-nouveau-svm-svmm-uaf-v2-1-8e6590519f07@gmail.com> X-B4-Tracking: v=1; b=H4sIACTnfmoC/4WNQQ6CMBBFr0Jm7RjaKhpX3sOwGMoANZaSljYaw t2leAAXf/GS//9bILA3HOBWLOA5mWDcuIE8FKAHGntG024MspRVeRUKRxcTU8SQbI7FSB02je5 UJaszEcE2nTx35r3fPuofh9g8Wc/5KzcGE2bnP7s3idz7o0gCBcpWCSFbpos63XtL5nXUzkK9r usX6v8BRsoAAAA= X-Change-ID: 20260813-nouveau-svm-svmm-uaf-bbcf36265aaa To: Lyude Paul , Danilo Krummrich , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Ben Skeggs Cc: dri-devel@lists.freedesktop.org, nouveau@lists.freedesktop.org, linux-kernel@vger.kernel.org, Yuhao Jiang , stable@vger.kernel.org, Zhenhao Wan X-Mailer: b4 0.15.2 X-Developer-Signature: v=1; a=ed25519-sha256; t=1786701615; l=3566; i=whi4ed0g@gmail.com; h=from:subject:message-id; bh=Xa5VtHj3w4sPlc/TppIcRh1BbFj+6tLTdDnsIWhMORY=; b=TBxXokJK8M7vP1OhEP1hGzukGoCRT8H3Zet+dNfTg4l0/uLvvpsPxPmHtEGUTfqyZsKlDo9E4 ofOpy7NU5suA8CQXNc7SFLTq0vitYWUEzCqlR4zth9V1vglhRYM545G X-Developer-Key: i=whi4ed0g@gmail.com; a=ed25519; pk=zRTKlstE0LmilshGwJsFYEVjiT6RiXMBXK8Og6VmuVQ= The SVM fault handler nouveau_svm_fault() looks up each fault's nouveau_svmm under svm->mutex, caches it in the fault array, then drops svm->mutex and dereferences the svmm across blocking faults (mmu_interval_notifier_insert(), hmm_range_fault()). nouveau_svmm is not refcounted. On DRM file close nouveau_svmm_fini() -> mmu_notifier_put() frees it asynchronously via call_srcu() without waiting for the handler, and mmget_not_zero() pins the mm, not the svmm. flush_work() on the fault buffer otherwise runs only at device removal and suspend, never on close, so a fault handled concurrently with a close can dereference a freed svmm. The instance is already unlinked by nouveau_svmm_part() earlier in the same close, so no new fault can resolve to it. Drain the handler in nouveau_svmm_fini() before the free, guarding the flush with a NULL check on drm->svm: on device teardown nouveau_svm_fini() runs first and frees drm->svm (NULL) after blocking the notify and flushing the buffer, so the handler is already drained; on per-client close drm->svm is alive and the flush runs. Fixes: eeaf06ac1a55 ("drm/nouveau/svm: initial support for shared virtual m= emory") Reported-by: Yuhao Jiang Assisted-by: Claude:claude-opus-5 Cc: stable@vger.kernel.org Signed-off-by: Zhenhao Wan Reviewed-by: Lyude Paul --- Changes in v2: - Fix a NULL deref introduced in v1: guard flush_work() with a NULL check on drm->svm. On device teardown nouveau_svm_fini() frees drm->svm before the per-client svmm teardown, so nouveau_svmm_fini() would deref NULL (reported by Sashiko AI review); the handler is already drained there, so there is nothing left to flush. - Tighten the commit message and the code comment; no functional change. - Link to v1: https://patch.msgid.link/20260813-nouveau-svm-svmm-uaf-v1-1-2= d3112dea734@gmail.com To: Lyude Paul To: Danilo Krummrich To: Maarten Lankhorst To: Maxime Ripard To: Thomas Zimmermann To: David Airlie To: Simona Vetter To: Ben Skeggs Cc: dri-devel@lists.freedesktop.org Cc: nouveau@lists.freedesktop.org Cc: linux-kernel@vger.kernel.org --- drivers/gpu/drm/nouveau/nouveau_svm.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouvea= u/nouveau_svm.c index dcc92131488e..a87406d3da30 100644 --- a/drivers/gpu/drm/nouveau/nouveau_svm.c +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c @@ -304,6 +304,19 @@ nouveau_svmm_fini(struct nouveau_svmm **psvmm) { struct nouveau_svmm *svmm =3D *psvmm; if (svmm) { + struct nouveau_svm *svm =3D svmm->vmm->cli->drm->svm; + + /* The fault handler caches svmm pointers under svm->mutex and + * dereferences them after dropping it, across blocking faults. + * The instance is already unlinked (nouveau_svmm_part), so drain + * the handler before the free to release any in-flight reference. + * + * On device teardown nouveau_svm_fini() ran first and freed + * drm->svm (NULL) after draining the buffer; nothing to flush. + */ + if (svm) + flush_work(&svm->buffer[0].work); + mutex_lock(&svmm->mutex); svmm->vmm =3D NULL; mutex_unlock(&svmm->mutex); --- base-commit: db2ddb87143519e20a95aa36c60b36107b736a58 change-id: 20260813-nouveau-svm-svmm-uaf-bbcf36265aaa Best regards, -- =20 Zhenhao Wan