drm/vmwgfx: Keep a gem reference to user bos in surfaces

Surfaces can be backed (i.e. stored in) memory objects (mob's) which
are created and managed by the userspace as GEM buffers. Surfaces
grab only a ttm reference which means that the gem object can
be deleted underneath us, especially in cases where prime buffer
export is used.

Make sure that all userspace surfaces which are backed by gem objects
hold a gem reference to make sure they're not deleted before vmw
surfaces are done with them, which fixes:
------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 2 PID: 2632 at lib/refcount.c:28 refcount_warn_saturate+0xfb/0x150
Modules linked in: overlay vsock_loopback vmw_vsock_virtio_transport_common vmw_vsock_vmci_transport vsock snd_ens1371 snd_ac97_codec ac97_bus snd_pcm gameport>
CPU: 2 PID: 2632 Comm: vmw_ref_count Not tainted 6.5.0-rc2-vmwgfx #1
Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
RIP: 0010:refcount_warn_saturate+0xfb/0x150
Code: eb 9e 0f b6 1d 8b 5b a6 01 80 fb 01 0f 87 ba e4 80 00 83 e3 01 75 89 48 c7 c7 c0 3c f9 a3 c6 05 6f 5b a6 01 01 e8 15 81 98 ff <0f> 0b e9 6f ff ff ff 0f b>
RSP: 0018:ffffbdc34344bba0 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000027
RDX: ffff960475ea1548 RSI: 0000000000000001 RDI: ffff960475ea1540
RBP: ffffbdc34344bba8 R08: 0000000000000003 R09: 65646e75203a745f
R10: ffffffffa5b32b20 R11: 72657466612d6573 R12: ffff96037d6a6400
R13: ffff9603484805b0 R14: 000000000000000b R15: ffff9603bed06060
FS:  00007f5fd8520c40(0000) GS:ffff960475e80000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5fda755000 CR3: 000000010d012005 CR4: 00000000003706e0
Call Trace:
 <TASK>
 ? show_regs+0x6e/0x80
 ? refcount_warn_saturate+0xfb/0x150
 ? __warn+0x91/0x150
 ? refcount_warn_saturate+0xfb/0x150
 ? report_bug+0x19d/0x1b0
 ? handle_bug+0x46/0x80
 ? exc_invalid_op+0x1d/0x80
 ? asm_exc_invalid_op+0x1f/0x30
 ? refcount_warn_saturate+0xfb/0x150
 drm_gem_object_handle_put_unlocked+0xba/0x110 [drm]
 drm_gem_object_release_handle+0x6e/0x80 [drm]
 drm_gem_handle_delete+0x6a/0xc0 [drm]
 ? __pfx_vmw_bo_unref_ioctl+0x10/0x10 [vmwgfx]
 vmw_bo_unref_ioctl+0x33/0x40 [vmwgfx]
 drm_ioctl_kernel+0xbc/0x160 [drm]
 drm_ioctl+0x2d2/0x580 [drm]
 ? __pfx_vmw_bo_unref_ioctl+0x10/0x10 [vmwgfx]
 ? do_vmi_munmap+0xee/0x180
 vmw_generic_ioctl+0xbd/0x180 [vmwgfx]
 vmw_unlocked_ioctl+0x19/0x20 [vmwgfx]
 __x64_sys_ioctl+0x99/0xd0
 do_syscall_64+0x5d/0x90
 ? syscall_exit_to_user_mode+0x2a/0x50
 ? do_syscall_64+0x6d/0x90
 ? handle_mm_fault+0x16e/0x2f0
 ? exit_to_user_mode_prepare+0x34/0x170
 ? irqentry_exit_to_user_mode+0xd/0x20
 ? irqentry_exit+0x3f/0x50
 ? exc_page_fault+0x8e/0x190
 entry_SYSCALL_64_after_hwframe+0x6e/0xd8
RIP: 0033:0x7f5fda51aaff
Code: 00 48 89 44 24 18 31 c0 48 8d 44 24 60 c7 04 24 10 00 00 00 48 89 44 24 08 48 8d 44 24 20 48 89 44 24 10 b8 10 00 00 00 0f 05 <41> 89 c0 3d 00 f0 ff ff 7>
RSP: 002b:00007ffd536a4d30 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007ffd536a4de0 RCX: 00007f5fda51aaff
RDX: 00007ffd536a4de0 RSI: 0000000040086442 RDI: 0000000000000003
RBP: 0000000040086442 R08: 000055fa603ada50 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffd536a51b8
R13: 0000000000000003 R14: 000055fa5ebb4c80 R15: 00007f5fda90f040
 </TASK>
---[ end trace 0000000000000000 ]---

A lot of the analyis on the bug was done by Murray McAllister and
Ian Forbes.

Reported-by: Murray McAllister <murray.mcallister@gmail.com>
Cc: Ian Forbes <iforbes@vmware.com>
Signed-off-by: Zack Rusin <zackr@vmware.com>
Fixes: a950b98 ("drm/vmwgfx: Do not drop the reference to the handle too soon")
Cc: <stable@vger.kernel.org> # v6.2+
Reviewed-by: Martin Krastev <krastevm@vmware.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230928041355.737635-1-zack@kde.org

drivers/gpu/drm/vmwgfx/vmwgfx_bo.c

@@ -34,6 +34,8 @@
 
 static void vmw_bo_release(struct vmw_bo *vbo)
 {
+	WARN_ON(vbo->tbo.base.funcs &&
+		kref_read(&vbo->tbo.base.refcount) != 0);
 	vmw_bo_unmap(vbo);
 	drm_gem_object_release(&vbo->tbo.base);
 }
@@ -497,7 +499,7 @@ static int vmw_user_bo_synccpu_release(struct drm_file *filp,
 		if (!(flags & drm_vmw_synccpu_allow_cs)) {
 			atomic_dec(&vmw_bo->cpu_writers);
 		}
-		vmw_user_bo_unref(vmw_bo);
+		vmw_user_bo_unref(&vmw_bo);
 	}
 
 	return ret;
@@ -539,7 +541,7 @@ int vmw_user_bo_synccpu_ioctl(struct drm_device *dev, void *data,
 			return ret;
 
 		ret = vmw_user_bo_synccpu_grab(vbo, arg->flags);
-		vmw_user_bo_unref(vbo);
+		vmw_user_bo_unref(&vbo);
 		if (unlikely(ret != 0)) {
 			if (ret == -ERESTARTSYS || ret == -EBUSY)
 				return -EBUSY;
@@ -612,7 +614,6 @@ int vmw_user_bo_lookup(struct drm_file *filp,
 	}
 
 	*out = to_vmw_bo(gobj);
-	ttm_bo_get(&(*out)->tbo);
 
 	return 0;
 }

drivers/gpu/drm/vmwgfx/vmwgfx_bo.h

@@ -195,12 +195,19 @@ static inline struct vmw_bo *vmw_bo_reference(struct vmw_bo *buf)
 	return buf;
 }
 
-static inline void vmw_user_bo_unref(struct vmw_bo *vbo)
+static inline struct vmw_bo *vmw_user_bo_ref(struct vmw_bo *vbo)
 {
-	if (vbo) {
-		ttm_bo_put(&vbo->tbo);
-		drm_gem_object_put(&vbo->tbo.base);
-	}
+	drm_gem_object_get(&vbo->tbo.base);
+	return vbo;
+}
+
+static inline void vmw_user_bo_unref(struct vmw_bo **buf)
+{
+	struct vmw_bo *tmp_buf = *buf;
+
+	*buf = NULL;
+	if (tmp_buf)
+		drm_gem_object_put(&tmp_buf->tbo.base);
 }
 
 static inline struct vmw_bo *to_vmw_bo(struct drm_gem_object *gobj)

drivers/gpu/drm/vmwgfx/vmwgfx_cotable.c

@@ -432,7 +432,7 @@ static int vmw_cotable_resize(struct vmw_resource *res, size_t new_size)
 	 * for the new COTable. Initially pin the buffer object to make sure
 	 * we can use tryreserve without failure.
 	 */
-	ret = vmw_bo_create(dev_priv, &bo_params, &buf);
+	ret = vmw_gem_object_create(dev_priv, &bo_params, &buf);
 	if (ret) {
 		DRM_ERROR("Failed initializing new cotable MOB.\n");
 		goto out_done;
@@ -502,7 +502,7 @@ static int vmw_cotable_resize(struct vmw_resource *res, size_t new_size)
 
 	vmw_resource_mob_attach(res);
 	/* Let go of the old mob. */
-	vmw_bo_unreference(&old_buf);
+	vmw_user_bo_unref(&old_buf);
 	res->id = vcotbl->type;
 
 	ret = dma_resv_reserve_fences(bo->base.resv, 1);
@@ -521,7 +521,7 @@ static int vmw_cotable_resize(struct vmw_resource *res, size_t new_size)
 out_wait:
 	ttm_bo_unpin(bo);
 	ttm_bo_unreserve(bo);
-	vmw_bo_unreference(&buf);
+	vmw_user_bo_unref(&buf);
 
 out_done:
 	MKS_STAT_TIME_POP(MKSSTAT_KERN_COTABLE_RESIZE);

drivers/gpu/drm/vmwgfx/vmwgfx_drv.h

@@ -853,6 +853,10 @@ static inline bool vmw_resource_mob_attached(const struct vmw_resource *res)
 /**
  * GEM related functionality - vmwgfx_gem.c
  */
+struct vmw_bo_params;
+int vmw_gem_object_create(struct vmw_private *vmw,
+			  struct vmw_bo_params *params,
+			  struct vmw_bo **p_vbo);
 extern int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
 					     struct drm_file *filp,
 					     uint32_t size,

drivers/gpu/drm/vmwgfx/vmwgfx_execbuf.c

@@ -1151,7 +1151,7 @@ static int vmw_translate_mob_ptr(struct vmw_private *dev_priv,
 				 SVGAMobId *id,
 				 struct vmw_bo **vmw_bo_p)
 {
-	struct vmw_bo *vmw_bo;
+	struct vmw_bo *vmw_bo, *tmp_bo;
 	uint32_t handle = *id;
 	struct vmw_relocation *reloc;
 	int ret;
@@ -1164,7 +1164,8 @@ static int vmw_translate_mob_ptr(struct vmw_private *dev_priv,
 	}
 	vmw_bo_placement_set(vmw_bo, VMW_BO_DOMAIN_MOB, VMW_BO_DOMAIN_MOB);
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo);
-	vmw_user_bo_unref(vmw_bo);
+	tmp_bo = vmw_bo;
+	vmw_user_bo_unref(&tmp_bo);
 	if (unlikely(ret != 0))
 		return ret;
 
@@ -1206,7 +1207,7 @@ static int vmw_translate_guest_ptr(struct vmw_private *dev_priv,
 				   SVGAGuestPtr *ptr,
 				   struct vmw_bo **vmw_bo_p)
 {
-	struct vmw_bo *vmw_bo;
+	struct vmw_bo *vmw_bo, *tmp_bo;
 	uint32_t handle = ptr->gmrId;
 	struct vmw_relocation *reloc;
 	int ret;
@@ -1220,7 +1221,8 @@ static int vmw_translate_guest_ptr(struct vmw_private *dev_priv,
 	vmw_bo_placement_set(vmw_bo, VMW_BO_DOMAIN_GMR | VMW_BO_DOMAIN_VRAM,
 			     VMW_BO_DOMAIN_GMR | VMW_BO_DOMAIN_VRAM);
 	ret = vmw_validation_add_bo(sw_context->ctx, vmw_bo);
-	vmw_user_bo_unref(vmw_bo);
+	tmp_bo = vmw_bo;
+	vmw_user_bo_unref(&tmp_bo);
 	if (unlikely(ret != 0))
 		return ret;
 

drivers/gpu/drm/vmwgfx/vmwgfx_gem.c

@@ -111,6 +111,20 @@ static const struct drm_gem_object_funcs vmw_gem_object_funcs = {
 	.vm_ops = &vmw_vm_ops,
 };
 
+int vmw_gem_object_create(struct vmw_private *vmw,
+			  struct vmw_bo_params *params,
+			  struct vmw_bo **p_vbo)
+{
+	int ret = vmw_bo_create(vmw, params, p_vbo);
+
+	if (ret != 0)
+		goto out_no_bo;
+
+	(*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
+out_no_bo:
+	return ret;
+}
+
 int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
 				      struct drm_file *filp,
 				      uint32_t size,
@@ -126,12 +140,10 @@ int vmw_gem_object_create_with_handle(struct vmw_private *dev_priv,
 		.pin = false
 	};
 
-	ret = vmw_bo_create(dev_priv, &params, p_vbo);
+	ret = vmw_gem_object_create(dev_priv, &params, p_vbo);
 	if (ret != 0)
 		goto out_no_bo;
 
-	(*p_vbo)->tbo.base.funcs = &vmw_gem_object_funcs;
-
 	ret = drm_gem_handle_create(filp, &(*p_vbo)->tbo.base, handle);
 out_no_bo:
 	return ret;

drivers/gpu/drm/vmwgfx/vmwgfx_kms.c

@@ -1471,8 +1471,8 @@ static int vmw_create_bo_proxy(struct drm_device *dev,
 	/* Reserve and switch the backing mob. */
 	mutex_lock(&res->dev_priv->cmdbuf_mutex);
 	(void) vmw_resource_reserve(res, false, true);
-	vmw_bo_unreference(&res->guest_memory_bo);
-	res->guest_memory_bo = vmw_bo_reference(bo_mob);
+	vmw_user_bo_unref(&res->guest_memory_bo);
+	res->guest_memory_bo = vmw_user_bo_ref(bo_mob);
 	res->guest_memory_offset = 0;
 	vmw_resource_unreserve(res, false, false, false, NULL, 0);
 	mutex_unlock(&res->dev_priv->cmdbuf_mutex);
@@ -1666,7 +1666,7 @@ static struct drm_framebuffer *vmw_kms_fb_create(struct drm_device *dev,
 err_out:
 	/* vmw_user_lookup_handle takes one ref so does new_fb */
 	if (bo)
-		vmw_user_bo_unref(bo);
+		vmw_user_bo_unref(&bo);
 	if (surface)
 		vmw_surface_unreference(&surface);
 

drivers/gpu/drm/vmwgfx/vmwgfx_overlay.c

@@ -451,7 +451,7 @@ int vmw_overlay_ioctl(struct drm_device *dev, void *data,
 
 	ret = vmw_overlay_update_stream(dev_priv, buf, arg, true);
 
-	vmw_user_bo_unref(buf);
+	vmw_user_bo_unref(&buf);
 
 out_unlock:
 	mutex_unlock(&overlay->mutex);

drivers/gpu/drm/vmwgfx/vmwgfx_resource.c

@@ -141,7 +141,7 @@ static void vmw_resource_release(struct kref *kref)
 		if (res->coherent)
 			vmw_bo_dirty_release(res->guest_memory_bo);
 		ttm_bo_unreserve(bo);
-		vmw_bo_unreference(&res->guest_memory_bo);
+		vmw_user_bo_unref(&res->guest_memory_bo);
 	}
 
 	if (likely(res->hw_destroy != NULL)) {
@@ -338,7 +338,7 @@ static int vmw_resource_buf_alloc(struct vmw_resource *res,
 		return 0;
 	}
 
-	ret = vmw_bo_create(res->dev_priv, &bo_params, &gbo);
+	ret = vmw_gem_object_create(res->dev_priv, &bo_params, &gbo);
 	if (unlikely(ret != 0))
 		goto out_no_bo;
 
@@ -457,11 +457,11 @@ void vmw_resource_unreserve(struct vmw_resource *res,
 			vmw_resource_mob_detach(res);
 			if (res->coherent)
 				vmw_bo_dirty_release(res->guest_memory_bo);
-			vmw_bo_unreference(&res->guest_memory_bo);
+			vmw_user_bo_unref(&res->guest_memory_bo);
 		}
 
 		if (new_guest_memory_bo) {
-			res->guest_memory_bo = vmw_bo_reference(new_guest_memory_bo);
+			res->guest_memory_bo = vmw_user_bo_ref(new_guest_memory_bo);
 
 			/*
 			 * The validation code should already have added a
@@ -551,7 +551,7 @@ vmw_resource_check_buffer(struct ww_acquire_ctx *ticket,
 	ttm_bo_put(val_buf->bo);
 	val_buf->bo = NULL;
 	if (guest_memory_dirty)
-		vmw_bo_unreference(&res->guest_memory_bo);
+		vmw_user_bo_unref(&res->guest_memory_bo);
 
 	return ret;
 }
@@ -727,7 +727,7 @@ int vmw_resource_validate(struct vmw_resource *res, bool intr,
 		goto out_no_validate;
 	else if (!res->func->needs_guest_memory && res->guest_memory_bo) {
 		WARN_ON_ONCE(vmw_resource_mob_attached(res));
-		vmw_bo_unreference(&res->guest_memory_bo);
+		vmw_user_bo_unref(&res->guest_memory_bo);
 	}
 
 	return 0;

drivers/gpu/drm/vmwgfx/vmwgfx_shader.c

@@ -180,7 +180,7 @@ static int vmw_gb_shader_init(struct vmw_private *dev_priv,
 
 	res->guest_memory_size = size;
 	if (byte_code) {
-		res->guest_memory_bo = vmw_bo_reference(byte_code);
+		res->guest_memory_bo = vmw_user_bo_ref(byte_code);
 		res->guest_memory_offset = offset;
 	}
 	shader->size = size;
@@ -809,7 +809,7 @@ static int vmw_shader_define(struct drm_device *dev, struct drm_file *file_priv,
 				    shader_type, num_input_sig,
 				    num_output_sig, tfile, shader_handle);
 out_bad_arg:
-	vmw_user_bo_unref(buffer);
+	vmw_user_bo_unref(&buffer);
 	return ret;
 }
 

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -686,9 +686,6 @@ static void vmw_user_surface_base_release(struct ttm_base_object **p_base)
 	    container_of(base, struct vmw_user_surface, prime.base);
 	struct vmw_resource *res = &user_srf->srf.res;
 
-	if (res->guest_memory_bo)
-		drm_gem_object_put(&res->guest_memory_bo->tbo.base);
-
 	*p_base = NULL;
 	vmw_resource_unreference(&res);
 }
@@ -855,23 +852,21 @@ int vmw_surface_define_ioctl(struct drm_device *dev, void *data,
 	 * expect a backup buffer to be present.
 	 */
 	if (dev_priv->has_mob && req->shareable) {
-		uint32_t backup_handle;
-
-		ret = vmw_gem_object_create_with_handle(dev_priv,
-							file_priv,
-							res->guest_memory_size,
-							&backup_handle,
-							&res->guest_memory_bo);
+		struct vmw_bo_params params = {
+			.domain = VMW_BO_DOMAIN_SYS,
+			.busy_domain = VMW_BO_DOMAIN_SYS,
+			.bo_type = ttm_bo_type_device,
+			.size = res->guest_memory_size,
+			.pin = false
+		};
+
+		ret = vmw_gem_object_create(dev_priv,
+					    &params,
+					    &res->guest_memory_bo);
 		if (unlikely(ret != 0)) {
 			vmw_resource_unreference(&res);
 			goto out_unlock;
 		}
-		vmw_bo_reference(res->guest_memory_bo);
-		/*
-		 * We don't expose the handle to the userspace and surface
-		 * already holds a gem reference
-		 */
-		drm_gem_handle_delete(file_priv, backup_handle);
 	}
 
 	tmp = vmw_resource_reference(&srf->res);
@@ -1512,7 +1507,7 @@ vmw_gb_surface_define_internal(struct drm_device *dev,
 		if (ret == 0) {
 			if (res->guest_memory_bo->tbo.base.size < res->guest_memory_size) {
 				VMW_DEBUG_USER("Surface backup buffer too small.\n");
-				vmw_bo_unreference(&res->guest_memory_bo);
+				vmw_user_bo_unref(&res->guest_memory_bo);
 				ret = -EINVAL;
 				goto out_unlock;
 			} else {
@@ -1526,8 +1521,6 @@ vmw_gb_surface_define_internal(struct drm_device *dev,
 							res->guest_memory_size,
 							&backup_handle,
 							&res->guest_memory_bo);
-		if (ret == 0)
-			vmw_bo_reference(res->guest_memory_bo);
 	}
 
 	if (unlikely(ret != 0)) {