Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues: - [Critical] Direct access to ctx->vm before lazy initialization causes a NULL pointer dereference. - [High] TOCTOU race in MSM_PARAM_EN_VM_BIND allows invalid VM configuration. -- --- Patch [1]: [PATCH v6 01/16] drm/msm: Fix barriers accessing ctx vm --- commit ca8b3357d768cc8c8e48035f7adbc82abd4eb8c7 Author: Rob Clark <[email protected]> drm/msm: Fix barriers accessing ctx vm Don't rely on store ordering to protect us from caller seeing a partially initialized vm. > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c > index 79f78e7e16e9d..3c8b5083a1fbe 100644 > --- a/drivers/gpu/drm/msm/msm_drv.c > +++ b/drivers/gpu/drm/msm/msm_drv.c > @@ -225,18 +225,19 @@ struct drm_gpuvm *msm_context_vm(struct drm_device > *dev, struct msm_context *ctx > { > static DEFINE_MUTEX(init_lock); > struct msm_drm_private *priv = dev->dev_private; > + struct drm_gpuvm *vm = smp_load_acquire(&ctx->vm); > > /* Once ctx->vm is created it is valid for the lifetime of the context: > */ > - if (ctx->vm) > - return ctx->vm; > + if (vm) > + return vm; > + > + guard(mutex)(&init_lock); > > - mutex_lock(&init_lock); > if (!ctx->vm) { > - ctx->vm = msm_gpu_create_private_vm( > + vm = msm_gpu_create_private_vm( > priv->gpu, current, !ctx->userspace_managed_vm); > - > + smp_store_release(&ctx->vm, vm); > } > - mutex_unlock(&init_lock); > > return ctx->vm; > } [Severity: Critical] This is a pre-existing issue, but I noticed that ctx->vm can be accessed directly before lazy initialization. If an unprivileged user opens the DRM device and immediately calls the MSM_GEM_SUBMIT IOCTL, it evaluates to_msm_vm(ctx->vm)->unusable without ensuring the VM has been initialized via msm_context_vm(): drivers/gpu/drm/msm/msm_gem_submit.c:msm_ioctl_gem_submit() { ... if (to_msm_vm(ctx->vm)->unusable) return UERR(EPIPE, dev, "context is unusable"); ... } Since ctx->vm is NULL, the to_msm_vm() macro computes an invalid pointer and dereferences its unusable field, causing a panic. Similarly, calling the MSM_GEM_NEW IOCTL with the MSM_BO_NO_SHARE flag executes drm_gpuvm_resv_obj(ctx->vm) which also dereferences NULL: drivers/gpu/drm/msm/msm_gem.c:msm_gem_new_handle() { ... if (flags & MSM_BO_NO_SHARE) { struct msm_context *ctx = file->driver_priv; struct drm_gem_object *r_obj = drm_gpuvm_resv_obj(ctx->vm); ... } Can these paths be updated to ensure the VM is initialized via msm_context_vm() before accessing it? [Severity: High] This isn't a bug introduced by this patch, but I found a potential TOCTOU race in MSM_PARAM_EN_VM_BIND that could allow an invalid VM configuration. In adreno_gpu_set_param(), it locklessly checks if (ctx->vm): drivers/gpu/drm/msm/adreno/adreno_gpu.c:adreno_gpu_set_param() { ... case MSM_PARAM_EN_VM_BIND: ... if (ctx->vm) return UERR(EBUSY, drm, "VM already created"); ctx->userspace_managed_vm = value; ... } If Thread A calls the MSM_SET_PARAM IOCTL, checks ctx->vm and sees NULL, and concurrently Thread B calls an IOCTL like MSM_INFO_GET_IOVA which calls msm_context_vm(), Thread B will create the VM as kernel-managed. Thread A then resumes and sets ctx->userspace_managed_vm = 1. Does this result in an inconsistent state where the context claims userspace management but the underlying VM is kernel-managed? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
