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

[Luben Tuikov <luben.tuikov@amd.com>]

On 2020-07-29 9:49 a.m., Alex Deucher wrote:
> 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.

There are quite a few of those under drivers/gpu/drm, for "amd/", "scheduler/"
drm*.c files,

$find . \( -regex "./drm.*\.c" -or -regex "./amd/.*\.c" -or -regex "./scheduler/.*\.c" \) -exec egrep -n -- " *= *{ *(|NULL|0) *}" \{\} \+ | wc -l
374
$_

Out of which only 16 are of the non-ISO C variety, "= {}",

$find . \( -regex "./drm.*\.c" -or -regex "./amd/.*\.c" -or -regex "./scheduler/.*\.c" \) -exec egrep -n -- " *= *{ *}" \{\} \+ | wc -l
16
$_

Perhaps the latter are the more pressing ones, since it is a C++ initializer and not a ISO C one.

Regards,
Luben



> 
> 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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