Re: [Linux-kernel-mentees] [PATCH] drm/amdgpu: Prevent kernel-infoleak in amdgpu_info_ioctl()

[Alex Deucher <alexdeucher@gmail.com>]

On Wed, Jul 29, 2020 at 4:11 AM Christian König
<ckoenig.leichtzumerken@gmail.com> wrote:
>
> Am 28.07.20 um 21:29 schrieb Peilin Ye:
> > Compiler leaves a 4-byte hole near the end of `dev_info`, causing
> > amdgpu_info_ioctl() to copy uninitialized kernel stack memory to userspace
> > when `size` is greater than 356.
> >
> > In 2015 we tried to fix this issue by doing `= {};` on `dev_info`, which
> > unfortunately does not initialize that 4-byte hole. Fix it by using
> > memset() instead.
> >
> > Cc: stable@vger.kernel.org
> > Fixes: c193fa91b918 ("drm/amdgpu: information leak in amdgpu_info_ioctl()")
> > Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
> > Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
> > Signed-off-by: Peilin Ye <yepeilin.cs@gmail.com>
>
> Reviewed-by: Christian König <christian.koenig@amd.com>
>
> I can't count how many of those we have fixed over the years.
>
> At some point we should probably document that using "= {}" or "= { 0 }"
> in the kernel is a really bad idea and should be avoided.

Moreover, it seems like different compilers seem to behave relatively
differently with these and we often get reports of warnings with these
on clang.  When in doubt, memset.

Alex

>
> Thanks,
> Christian.
>
> > ---
> > $ pahole -C "drm_amdgpu_info_device" drivers/gpu/drm/amd/amdgpu/amdgpu_kms.o
> > struct drm_amdgpu_info_device {
> >       __u32                      device_id;            /*     0     4 */
> >       __u32                      chip_rev;             /*     4     4 */
> >       __u32                      external_rev;         /*     8     4 */
> >       __u32                      pci_rev;              /*    12     4 */
> >       __u32                      family;               /*    16     4 */
> >       __u32                      num_shader_engines;   /*    20     4 */
> >       __u32                      num_shader_arrays_per_engine; /*    24     4 */
> >       __u32                      gpu_counter_freq;     /*    28     4 */
> >       __u64                      max_engine_clock;     /*    32     8 */
> >       __u64                      max_memory_clock;     /*    40     8 */
> >       __u32                      cu_active_number;     /*    48     4 */
> >       __u32                      cu_ao_mask;           /*    52     4 */
> >       __u32                      cu_bitmap[4][4];      /*    56    64 */
> >       /* --- cacheline 1 boundary (64 bytes) was 56 bytes ago --- */
> >       __u32                      enabled_rb_pipes_mask; /*   120     4 */
> >       __u32                      num_rb_pipes;         /*   124     4 */
> >       /* --- cacheline 2 boundary (128 bytes) --- */
> >       __u32                      num_hw_gfx_contexts;  /*   128     4 */
> >       __u32                      _pad;                 /*   132     4 */
> >       __u64                      ids_flags;            /*   136     8 */
> >       __u64                      virtual_address_offset; /*   144     8 */
> >       __u64                      virtual_address_max;  /*   152     8 */
> >       __u32                      virtual_address_alignment; /*   160     4 */
> >       __u32                      pte_fragment_size;    /*   164     4 */
> >       __u32                      gart_page_size;       /*   168     4 */
> >       __u32                      ce_ram_size;          /*   172     4 */
> >       __u32                      vram_type;            /*   176     4 */
> >       __u32                      vram_bit_width;       /*   180     4 */
> >       __u32                      vce_harvest_config;   /*   184     4 */
> >       __u32                      gc_double_offchip_lds_buf; /*   188     4 */
> >       /* --- cacheline 3 boundary (192 bytes) --- */
> >       __u64                      prim_buf_gpu_addr;    /*   192     8 */
> >       __u64                      pos_buf_gpu_addr;     /*   200     8 */
> >       __u64                      cntl_sb_buf_gpu_addr; /*   208     8 */
> >       __u64                      param_buf_gpu_addr;   /*   216     8 */
> >       __u32                      prim_buf_size;        /*   224     4 */
> >       __u32                      pos_buf_size;         /*   228     4 */
> >       __u32                      cntl_sb_buf_size;     /*   232     4 */
> >       __u32                      param_buf_size;       /*   236     4 */
> >       __u32                      wave_front_size;      /*   240     4 */
> >       __u32                      num_shader_visible_vgprs; /*   244     4 */
> >       __u32                      num_cu_per_sh;        /*   248     4 */
> >       __u32                      num_tcc_blocks;       /*   252     4 */
> >       /* --- cacheline 4 boundary (256 bytes) --- */
> >       __u32                      gs_vgt_table_depth;   /*   256     4 */
> >       __u32                      gs_prim_buffer_depth; /*   260     4 */
> >       __u32                      max_gs_waves_per_vgt; /*   264     4 */
> >       __u32                      _pad1;                /*   268     4 */
> >       __u32                      cu_ao_bitmap[4][4];   /*   272    64 */
> >       /* --- cacheline 5 boundary (320 bytes) was 16 bytes ago --- */
> >       __u64                      high_va_offset;       /*   336     8 */
> >       __u64                      high_va_max;          /*   344     8 */
> >       __u32                      pa_sc_tile_steering_override; /*   352     4 */
> >
> >       /* XXX 4 bytes hole, try to pack */
> >
> >       __u64                      tcc_disabled_mask;    /*   360     8 */
> >
> >       /* size: 368, cachelines: 6, members: 49 */
> >       /* sum members: 364, holes: 1, sum holes: 4 */
> >       /* last cacheline: 48 bytes */
> > };
> >
> >   drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > index a8c47aecd342..0047da06041f 100644
> > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_kms.c
> > @@ -707,9 +707,10 @@ static int amdgpu_info_ioctl(struct drm_device *dev, void *data, struct drm_file
> >               return n ? -EFAULT : 0;
> >       }
> >       case AMDGPU_INFO_DEV_INFO: {
> > -             struct drm_amdgpu_info_device dev_info = {};
> > +             struct drm_amdgpu_info_device dev_info;
> >               uint64_t vm_size;
> >
> > +             memset(&dev_info, 0, sizeof(dev_info));
> >               dev_info.device_id = dev->pdev->device;
> >               dev_info.chip_rev = adev->rev_id;
> >               dev_info.external_rev = adev->external_rev_id;
>
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