drm/imagination: acquire vm_ctx->lock before mapping memory to GPU VM

The drm gpuvm code doesn't protect find operation against map operation,
and the driver needs to ensure a map operation shouldn't happen when a
find operation is in progress.

In some cases a find operation will be in progress when doing map/unmap
operations, and the find operation will do a NULL pointer dereference.

An example of the stack trace of such NULL dereference is shown below:

```
Unable to handle kernel access to user memory without uaccess routines at
virtual address 0000000000000010

[<ffffffff01e989d4>] drm_gpuva_find+0x28/0x6c [drm_gpuvm]
[<ffffffff01ed3a40>] pvr_vm_unmap+0x34/0x68 [powervr]
[<ffffffff01ec69da>] pvr_ioctl_vm_unmap+0x2e/0x50 [powervr]
[<ffffffff8080ce0a>] drm_ioctl_kernel+0x8e/0xdc
[<ffffffff8080d016>] drm_ioctl+0x1be/0x3e0
[<ffffffff802bec3e>] __riscv_sys_ioctl+0xba/0xc4
[<ffffffff80d858b2>] do_trap_ecall_u+0x23e/0x3f4
[<ffffffff80d92288>] handle_exception+0x168/0x174
```

As all occurences of drm_gpuva_find*() are already guarded by
vm_ctx->lock, make pvr_vm_map() to acquire this lock to prevent
disturbing any find operation. This fixes the NULL deference problem in
drm_gpuva_find*().

Cc: stable@vger.kernel.org
Fixes: ff5f643de0bf ("drm/imagination: Add GEM and VM related code")
Fixes: 4bc736f890ce ("drm/imagination: vm: make use of GPUVM's drm_exec helper")
Signed-off-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
Reviewed-by: Alessio Belle <alessio.belle@imgtec.com>
Link: https://patch.msgid.link/20260714073641.1935075-1-zhengxingda@iscas.ac.cn
Signed-off-by: Alessio Belle <alessio.belle@imgtec.com>

diff --git a/drivers/gpu/drm/imagination/pvr_vm.c b/drivers/gpu/drm/imagination/pvr_vm.c
index 396d349fb6ce48a91be2bac369b3be02980dbacb..ceb78694cd98738e47df8cce5a5f87b1368785ed 100644 (file)
--- a/drivers/gpu/drm/imagination/pvr_vm.c
+++ b/drivers/gpu/drm/imagination/pvr_vm.c
@@ -747,6 +747,7 @@ pvr_vm_map(struct pvr_vm_context *vm_ctx, struct pvr_gem_object *pvr_obj,
 
        pvr_gem_object_get(pvr_obj);
 
+       mutex_lock(&vm_ctx->lock);
        err = drm_gpuvm_exec_lock(&vm_exec);
        if (err)
                goto err_cleanup;
@@ -756,6 +757,7 @@ pvr_vm_map(struct pvr_vm_context *vm_ctx, struct pvr_gem_object *pvr_obj,
        drm_gpuvm_exec_unlock(&vm_exec);
 
 err_cleanup:
+       mutex_unlock(&vm_ctx->lock);
        pvr_vm_bind_op_fini(&bind_op);
 
        return err;