Hi Christian:

The warning is from the kernel test robot, I quote it here. The key point is that vm may be used in radeon_vm_fini(rdev, vm) without initialization. Although it is not possible in practice, I still add initializations to silence the warning of llvm.

---------- Forwarded message ---------
From: kernel test robot <lkp@intel.com>
Date: Wed, Dec 1, 2021 at 4:32 AM
Subject: drivers/gpu/drm/radeon/radeon_kms.c:672:7: warning: variable 'vm' is used uninitialized whenever 'if' condition is false
To: Zhou Qingyang <zhou1615@umn.edu>
Cc: <llvm@lists.linux.dev>, <kbuild-all@lists.01.org>, <linux-kernel@vger.kernel.org>, 0day robot <lkp@intel.com>

tree:   https://github.com/0day-ci/linux/commits/UPDATE-20211130-233655/Zhou-Qingyang/drm-radeon-radeon_kms-Fix-a-NULL-pointer-dereference-in-radeon_driver_open_kms/20211130-231509
head:   123fb3d217e89c4388fdb08b63991bac7c324219
commit: 123fb3d217e89c4388fdb08b63991bac7c324219 drm/radeon/radeon_kms: Fix a NULL pointer dereference in radeon_driver_open_kms()
date:   5 hours ago
config: mips-randconfig-r014-20211128 (https://download.01.org/0day-ci/archive/20211201/202112010420.xkXHciHS-lkp@intel.com/config)
compiler: clang version 14.0.0 (https://github.com/llvm/llvm-project 25eb7fa01d7ebbe67648ea03841cda55b4239ab2)
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # install mips cross compiling tool for clang build
        # apt-get install binutils-mips-linux-gnu
        # https://github.com/0day-ci/linux/commit/123fb3d217e89c4388fdb08b63991bac7c324219
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review UPDATE-20211130-233655/Zhou-Qingyang/drm-radeon-radeon_kms-Fix-a-NULL-pointer-dereference-in-radeon_driver_open_kms/20211130-231509
        git checkout 123fb3d217e89c4388fdb08b63991bac7c324219
        # save the config file to linux build tree
        mkdir build_dir
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=mips SHELL=/bin/bash drivers/gpu/drm/radeon/

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

>> drivers/gpu/drm/radeon/radeon_kms.c:672:7: warning: variable 'vm' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
                   if (rdev->accel_working) {
                       ^~~~~~~~~~~~~~~~~~~
   drivers/gpu/drm/radeon/radeon_kms.c:705:23: note: uninitialized use occurs here
           radeon_vm_fini(rdev, vm);
                                ^~
   drivers/gpu/drm/radeon/radeon_kms.c:672:3: note: remove the 'if' if its condition is always true
                   if (rdev->accel_working) {
                   ^~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/gpu/drm/radeon/radeon_kms.c:664:6: warning: variable 'vm' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
           if (rdev->family >= CHIP_CAYMAN) {
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/gpu/drm/radeon/radeon_kms.c:705:23: note: uninitialized use occurs here
           radeon_vm_fini(rdev, vm);
                                ^~
   drivers/gpu/drm/radeon/radeon_kms.c:664:2: note: remove the 'if' if its condition is always true
           if (rdev->family >= CHIP_CAYMAN) {
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   drivers/gpu/drm/radeon/radeon_kms.c:653:22: note: initialize the variable 'vm' to silence this warning
           struct radeon_vm *vm;
                               ^
                                = NULL
   2 warnings generated.


vim +672 drivers/gpu/drm/radeon/radeon_kms.c

771fe6b912fca54 Jerome Glisse      2009-06-05  638 
f482a1419545ded Alex Deucher       2012-07-17  639  /**
f482a1419545ded Alex Deucher       2012-07-17  640   * radeon_driver_open_kms - drm callback for open
f482a1419545ded Alex Deucher       2012-07-17  641   *
f482a1419545ded Alex Deucher       2012-07-17  642   * @dev: drm dev pointer
f482a1419545ded Alex Deucher       2012-07-17  643   * @file_priv: drm file
f482a1419545ded Alex Deucher       2012-07-17  644   *
f482a1419545ded Alex Deucher       2012-07-17  645   * On device open, init vm on cayman+ (all asics).
f482a1419545ded Alex Deucher       2012-07-17  646   * Returns 0 on success, error on failure.
f482a1419545ded Alex Deucher       2012-07-17  647   */
771fe6b912fca54 Jerome Glisse      2009-06-05  648  int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
771fe6b912fca54 Jerome Glisse      2009-06-05  649  {
721604a15b934f0 Jerome Glisse      2012-01-05  650      struct radeon_device *rdev = dev->dev_private;
10ebc0bc09344ab Dave Airlie        2012-09-17  651      int r;
123fb3d217e89c4 Zhou Qingyang      2021-11-30  652      struct radeon_fpriv *fpriv;
123fb3d217e89c4 Zhou Qingyang      2021-11-30  653      struct radeon_vm *vm;
721604a15b934f0 Jerome Glisse      2012-01-05  654 
721604a15b934f0 Jerome Glisse      2012-01-05  655      file_priv->driver_priv = NULL;
721604a15b934f0 Jerome Glisse      2012-01-05  656 
10ebc0bc09344ab Dave Airlie        2012-09-17  657      r = pm_runtime_get_sync(dev->dev);
9fb10671011143d Aditya Pakki       2020-06-13  658      if (r < 0) {
9fb10671011143d Aditya Pakki       2020-06-13  659              pm_runtime_put_autosuspend(dev->dev);
10ebc0bc09344ab Dave Airlie        2012-09-17  660              return r;
9fb10671011143d Aditya Pakki       2020-06-13  661      }
10ebc0bc09344ab Dave Airlie        2012-09-17  662 
721604a15b934f0 Jerome Glisse      2012-01-05  663      /* new gpu have virtual address space support */
721604a15b934f0 Jerome Glisse      2012-01-05  664      if (rdev->family >= CHIP_CAYMAN) {
721604a15b934f0 Jerome Glisse      2012-01-05  665 
721604a15b934f0 Jerome Glisse      2012-01-05  666              fpriv = kzalloc(sizeof(*fpriv), GFP_KERNEL);
721604a15b934f0 Jerome Glisse      2012-01-05  667              if (unlikely(!fpriv)) {
32c59dc14b72803 Alex Deucher       2016-08-31  668                      r = -ENOMEM;
32c59dc14b72803 Alex Deucher       2016-08-31  669                      goto out_suspend;
721604a15b934f0 Jerome Glisse      2012-01-05  670              }
721604a15b934f0 Jerome Glisse      2012-01-05  671 
544143f9e01a60a Alex Deucher       2015-01-28 @672              if (rdev->accel_working) {
cc9e67e3d7000c1 Christian König    2014-07-18  673                      vm = &fpriv->vm;
cc9e67e3d7000c1 Christian König    2014-07-18  674                      r = radeon_vm_init(rdev, vm);
74073c9dd299056 Quentin Casasnovas 2014-03-18  675                      if (r) {
123fb3d217e89c4 Zhou Qingyang      2021-11-30  676                              goto out_fpriv;
74073c9dd299056 Quentin Casasnovas 2014-03-18  677                      }
d72d43cfc5847c1 Christian König    2012-10-09  678 
f1e3dc708aaadb9 Christian König    2014-02-20  679                      r = radeon_bo_reserve(rdev->ring_tmp_bo.bo, false);
74073c9dd299056 Quentin Casasnovas 2014-03-18  680                      if (r) {
123fb3d217e89c4 Zhou Qingyang      2021-11-30  681                              goto out_vm_fini;
74073c9dd299056 Quentin Casasnovas 2014-03-18  682                      }
f1e3dc708aaadb9 Christian König    2014-02-20  683 
d72d43cfc5847c1 Christian König    2012-10-09  684                      /* map the ib pool buffer read only into
d72d43cfc5847c1 Christian König    2012-10-09  685                       * virtual address space */
cc9e67e3d7000c1 Christian König    2014-07-18  686                      vm->ib_bo_va = radeon_vm_bo_add(rdev, vm,
d72d43cfc5847c1 Christian König    2012-10-09  687                                                      rdev->ring_tmp_bo.bo);
123fb3d217e89c4 Zhou Qingyang      2021-11-30  688                      if (!vm->ib_bo_va) {
123fb3d217e89c4 Zhou Qingyang      2021-11-30  689                              r = -ENOMEM;
123fb3d217e89c4 Zhou Qingyang      2021-11-30  690                              goto out_vm_fini;
123fb3d217e89c4 Zhou Qingyang      2021-11-30  691                      }
123fb3d217e89c4 Zhou Qingyang      2021-11-30  692 
cc9e67e3d7000c1 Christian König    2014-07-18  693                      r = radeon_vm_bo_set_addr(rdev, vm->ib_bo_va,
cc9e67e3d7000c1 Christian König    2014-07-18  694                                                RADEON_VA_IB_OFFSET,
d72d43cfc5847c1 Christian König    2012-10-09  695                                                RADEON_VM_PAGE_READABLE |
d72d43cfc5847c1 Christian König    2012-10-09  696                                                RADEON_VM_PAGE_SNOOPED);
721604a15b934f0 Jerome Glisse      2012-01-05  697                      if (r) {
123fb3d217e89c4 Zhou Qingyang      2021-11-30  698                              goto out_vm_fini;
721604a15b934f0 Jerome Glisse      2012-01-05  699                      }
24f47acc78b0ab5 Jérôme Glisse      2014-05-07  700              }
721604a15b934f0 Jerome Glisse      2012-01-05  701              file_priv->driver_priv = fpriv;
721604a15b934f0 Jerome Glisse      2012-01-05  702      }
10ebc0bc09344ab Dave Airlie        2012-09-17  703 
123fb3d217e89c4 Zhou Qingyang      2021-11-30  704  out_vm_fini:
123fb3d217e89c4 Zhou Qingyang      2021-11-30  705      radeon_vm_fini(rdev, vm);
123fb3d217e89c4 Zhou Qingyang      2021-11-30  706  out_fpriv:
123fb3d217e89c4 Zhou Qingyang      2021-11-30  707      kfree(fpriv);
32c59dc14b72803 Alex Deucher       2016-08-31  708  out_suspend:
10ebc0bc09344ab Dave Airlie        2012-09-17  709      pm_runtime_mark_last_busy(dev->dev);
10ebc0bc09344ab Dave Airlie        2012-09-17  710      pm_runtime_put_autosuspend(dev->dev);
32c59dc14b72803 Alex Deucher       2016-08-31  711      return r;
771fe6b912fca54 Jerome Glisse      2009-06-05  712  }
771fe6b912fca54 Jerome Glisse      2009-06-05  713 

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org

On Wed, Dec 1, 2021 at 3:20 PM Christian König <christian.koenig@amd.com> wrote:

Am 01.12.21 um 04:22 schrieb Zhou Qingyang:
> In radeon_driver_open_kms(), radeon_vm_bo_add() is assigned to
> vm->ib_bo_va and passes and used in radeon_vm_bo_set_addr(). In
> radeon_vm_bo_set_addr(), there is a dereference of vm->ib_bo_va,
> which could lead to a NULL pointer dereference on failure of
> radeon_vm_bo_add().
>
> Fix this bug by adding a check of vm->ib_bo_va.
>
> This bug was found by a static analyzer. The analysis employs
> differential checking to identify inconsistent security operations
> (e.g., checks or kfrees) between two code paths and confirms that the
> inconsistent operations are not recovered in the current function or
> the callers, so they constitute bugs.
>
> Note that, as a bug found by static analysis, it can be a false
> positive or hard to trigger. Multiple researchers have cross-reviewed
> the bug.
>
> Builds with CONFIG_DRM_RADEON=m show no new warnings,
> and our static analyzer no longer warns about this code.
>
> Fixes: cc9e67e3d700 ("drm/radeon: fix VM IB handling")
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Zhou Qingyang <zhou1615@umn.edu>
> ---
> Changes in v2:
>    -  Initialize the variables to silence warning

What warning do you get? Double checking the code that shouldn't be
necessary and is usually rather frowned upon.

Thanks,
Christian.

>
> Changes in v3:
>    -  Fix the bug that good case will also be freed
>    -  Improve code style
>
> Changes in v2:
>    -  Improve the error handling into goto style
>
>   drivers/gpu/drm/radeon/radeon_kms.c | 37 ++++++++++++++++-------------
>   1 file changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/radeon_kms.c b/drivers/gpu/drm/radeon/radeon_kms.c
> index 482fb0ae6cb5..9d0f840286a1 100644
> --- a/drivers/gpu/drm/radeon/radeon_kms.c
> +++ b/drivers/gpu/drm/radeon/radeon_kms.c
> @@ -648,7 +648,9 @@ void radeon_driver_lastclose_kms(struct drm_device *dev)
>   int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
>   {
>       struct radeon_device *rdev = dev->dev_private;
> -     int r;
> +     struct radeon_fpriv *fpriv = NULL;
> +     struct radeon_vm *vm = NULL;
> +     int r = 0;
>
>       file_priv->driver_priv = NULL;
>
> @@ -660,8 +662,6 @@ int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
>   
>       /* new gpu have virtual address space support */
>       if (rdev->family >= CHIP_CAYMAN) {
> -             struct radeon_fpriv *fpriv;
> -             struct radeon_vm *vm;
>   
>               fpriv = kzalloc(sizeof(*fpriv), GFP_KERNEL);
>               if (unlikely(!fpriv)) {
> @@ -672,35 +672,38 @@ int radeon_driver_open_kms(struct drm_device *dev, struct drm_file *file_priv)
>               if (rdev->accel_working) {
>                       vm = &fpriv->vm;
>                       r = radeon_vm_init(rdev, vm);
> -                     if (r) {
> -                             kfree(fpriv);
> -                             goto out_suspend;
> -                     }
> +                     if (r)
> +                             goto out_fpriv;
>   
>                       r = radeon_bo_reserve(rdev->ring_tmp_bo.bo, false);
> -                     if (r) {
> -                             radeon_vm_fini(rdev, vm);
> -                             kfree(fpriv);
> -                             goto out_suspend;
> -                     }
> +                     if (r)
> +                             goto out_vm_fini;
>   
>                       /* map the ib pool buffer read only into
>                        * virtual address space */
>                       vm->ib_bo_va = radeon_vm_bo_add(rdev, vm,
>                                                       rdev->ring_tmp_bo.bo);
> +                     if (!vm->ib_bo_va) {
> +                             r = -ENOMEM;
> +                             goto out_vm_fini;
> +                     }
> +
>                       r = radeon_vm_bo_set_addr(rdev, vm->ib_bo_va,
>                                                 RADEON_VA_IB_OFFSET,
>                                                 RADEON_VM_PAGE_READABLE |
>                                                 RADEON_VM_PAGE_SNOOPED);
> -                     if (r) {
> -                             radeon_vm_fini(rdev, vm);
> -                             kfree(fpriv);
> -                             goto out_suspend;
> -                     }
> +                     if (r)
> +                             goto out_vm_fini;
>               }
>               file_priv->driver_priv = fpriv;
>       }
>   
> +out_vm_fini:
> +     if (r)
> +             radeon_vm_fini(rdev, vm);
> +out_fpriv:
> +     if (r)
> +             kfree(fpriv);
>   out_suspend:
>       pm_runtime_mark_last_busy(dev->dev);
>       pm_runtime_put_autosuspend(dev->dev);