Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
Pre-existing issues: - [High] The newly introduced `ready` flag check can be bypassed because `chan->fence` is published without a release barrier by the backend allocators, allowing a concurrent `nouveau_channel_kill()` to observe pre-initialization garbage. - [High] A concurrent channel kill event can trigger a Use-After-Free if fence context initialization fails because the kill event is armed prior to full initialization. -- --- Patch [2]: [PATCH v4 2/3] drm/nouveau: don't kill a fence context that is not ready yet --- commit 566dba46ab74848a1cc990a88e4d8e18c316f52d Author: Marek Czernohous <[email protected]> drm/nouveau: don't kill a fence context that is not ready yet This commit introduces a ready flag to the fence context to prevent the kill handler from taking an uninitialized lock. It uses smp_store_release() and smp_load_acquire() to hand over the context safely once it is fully built. A channel killed during initialization is recorded and processed once armed. > diff --git a/drivers/gpu/drm/nouveau/nouveau_chan.c > b/drivers/gpu/drm/nouveau/nouveau_chan.c > --- a/drivers/gpu/drm/nouveau/nouveau_chan.c > +++ b/drivers/gpu/drm/nouveau/nouveau_chan.c > @@ -43,9 +43,17 @@ module_param_named(vram_pushbuf, nouveau_vram_pushbuf, > int, 0400); > void > nouveau_channel_kill(struct nouveau_channel *chan) > { > + struct nouveau_fence_chan *fctx; > + > atomic_set(&chan->killed, 1); > - if (chan->fence) > - nouveau_fence_context_kill(chan->fence, -ENODEV); > + > + /* Pairs with the smp_mb() in nouveau_fence_context_arm(). */ > + smp_mb(); > + > + fctx = READ_ONCE(chan->fence); > + /* Pairs with the smp_store_release() there. */ > + if (fctx && smp_load_acquire(&fctx->ready)) [Severity: High] This is a pre-existing issue, but can we read pre-initialization garbage for fctx->ready here? Because chan->fence is published by backend allocators with a plain store (e.g., chan->fence = kzalloc_obj(*fctx)), on weakly-ordered architectures, this READ_ONCE() might observe the pointer before the allocator's zeroing stores are visible. The smp_load_acquire() on fctx->ready doesn't prevent reading pre-initialization garbage for the ready flag itself. If ready is read as non-zero garbage, the kill handler would proceed to acquire an uninitialized spinlock, potentially causing a kernel panic. > + nouveau_fence_context_kill(fctx, -ENODEV); > } [ ... ] > @@ -494,7 +502,12 @@ nouveau_channel_init(struct nouveau_channel *chan, u32 > vram, u32 gart) > } > > /* initialise synchronisation */ > - return nouveau_fence(drm)->context_new(chan); > + ret = nouveau_fence(drm)->context_new(chan); > + if (ret) > + return ret; [Severity: High] This isn't a bug introduced by this patch, but could this error path lead to a use-after-free if a concurrent channel kill event fires? Earlier in nouveau_channel_init(), the kill event is armed: drivers/gpu/drm/nouveau/nouveau_chan.c:nouveau_channel_init() { ... if (ret == 0) ret = nvif_event_allow(&chan->kill); ... } If context_new() fails (e.g., due to VMA allocation failure), it cleans up by freeing the fence context. If a hardware kill event fires concurrently, nouveau_channel_kill() might read chan->fence before the error path clears it. This would lead to a use-after-free when smp_load_acquire(&fctx->ready) is evaluated on the freed pointer in the asynchronous kill handler. > + > + nouveau_fence_context_arm(chan); > + return 0; > } -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=2
