[PATCH] drm/amd: Guard against bad data for ATIF ACPI method

[Alex Deucher]

On Fri, Oct 11, 2024 at 1:33 PM Mario Limonciello
<mario.limonciello at amd.com> wrote:
>
> If a BIOS provides bad data in response to an ATIF method call
> this causes a NULL pointer dereference in the caller.
>
> ```
> ? show_regs (arch/x86/kernel/dumpstack.c:478 (discriminator 1))
> ? __die (arch/x86/kernel/dumpstack.c:423 arch/x86/kernel/dumpstack.c:434)
> ? page_fault_oops (arch/x86/mm/fault.c:544 (discriminator 2) arch/x86/mm/fault.c:705 (discriminator 2))
> ? do_user_addr_fault (arch/x86/mm/fault.c:440 (discriminator 1) arch/x86/mm/fault.c:1232 (discriminator 1))
> ? acpi_ut_update_object_reference (drivers/acpi/acpica/utdelete.c:642)
> ? exc_page_fault (arch/x86/mm/fault.c:1542)
> ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623)
> ? amdgpu_atif_query_backlight_caps.constprop.0 (drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:387 (discriminator 2)) amdgpu
> ? amdgpu_atif_query_backlight_caps.constprop.0 (drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c:386 (discriminator 1)) amdgpu
> ```
>
> It has been encountered on at least one system, so guard for it.
>
> Cc: stable at vger.kernel.org
> Fixes: d38ceaf99ed0 ("drm/amdgpu: add core driver (v4)")
> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>

Acked-by: Alex Deucher <alexander.deucher at amd.com>

> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 15 ++++++++++++---
>  1 file changed, 12 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> index f85ace0384d2..1f5a296f5ed2 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
> @@ -147,6 +147,7 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
>                                            struct acpi_buffer *params)
>  {
>         acpi_status status;
> +       union acpi_object *obj;
>         union acpi_object atif_arg_elements[2];
>         struct acpi_object_list atif_arg;
>         struct acpi_buffer buffer = { ACPI_ALLOCATE_BUFFER, NULL };
> @@ -169,16 +170,24 @@ static union acpi_object *amdgpu_atif_call(struct amdgpu_atif *atif,
>
>         status = acpi_evaluate_object(atif->handle, NULL, &atif_arg,
>                                       &buffer);
> +       obj = (union acpi_object *)buffer.pointer;
>
> -       /* Fail only if calling the method fails and ATIF is supported */
> +       /* Fail if calling the method fails and ATIF is supported */
>         if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
>                 DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>                                  acpi_format_exception(status));
> -               kfree(buffer.pointer);
> +               kfree(obj);
>                 return NULL;
>         }
>
> -       return buffer.pointer;
> +       if (obj->type != ACPI_TYPE_BUFFER) {
> +               DRM_DEBUG_DRIVER("bad object returned from ATIF: %d\n",
> +                                obj->type);
> +               kfree(obj);
> +               return NULL;
> +       }
> +
> +       return obj;
>  }
>
>  /**
> --
> 2.43.0
>