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 deference. An example of the stack trace of such NULL deference 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: [email protected] 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 <[email protected]> --- Changes in v2: - Dropped wrongly duplicated mutex_unlock() call and reordered it to before pvr_vm_bind_op_fini() (the lock is acquired after pvr_vm_bind_op_map_init() call). (Thanks to Brajesh) - Added a extra Fixes pointing to the original broken code that was refactored by the original Fixes (but still broken). (Thanks to Alessio) - Fixed some typos in commit message. (Thanks to Alessio) - Added a stacktrace of the oops that occured on my board. (As suggested by Alessio) drivers/gpu/drm/imagination/pvr_vm.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/drivers/gpu/drm/imagination/pvr_vm.c b/drivers/gpu/drm/imagination/pvr_vm.c index 396d349fb6ce4..ceb78694cd987 100644 --- 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; -- 2.52.0
