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Message-ID: <32298ecd-7b7c-4e19-8481-f35249d6e076@amd.com>
Date: Thu, 31 Oct 2024 09:41:57 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Antonio Quartulli <antonio@...delbit.com>
Cc: amd-gfx@...ts.freedesktop.org, alexander.deucher@....com,
christian.koenig@....com, Xinhui.Pan@....com,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] amdgpu: prevent NULL pointer dereference if ATIF is not
supported
On 10/30/2024 16:06, Antonio Quartulli wrote:
> Hi Mario,
>
> On 30/10/2024 02:41, Mario Limonciello wrote:
>> On 10/29/2024 18:32, Antonio Quartulli wrote:
>>> acpi_evaluate_object() may return AE_NOT_FOUND (failure), which
>>> would result in dereferencing buffer.pointer (obj) while being NULL.
>>>
>>> Bail out also when status is AE_NOT_FOUND with a proper error message.
>>>
>>> This fixes 1 FORWARD_NULL issue reported by Coverity
>>> Report: CID 1600951: Null pointer dereferences (FORWARD_NULL)
>>>
>>> Signed-off-by: Antonio Quartulli <antonio@...delbit.com>
>>
>> I'm not really sure how realistic this failure is. Can you share the
>> full call trace that Coverity identified?
>
> I just checked Coverity Scan and it only says:
>
> 5. Condition status, taking true branch.
> 6. Condition status != 5U /* (acpi_status)(5 | 0) */, taking false
> branch.
>
> The above points are related to:
>
> if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
>
> It doesn't show how acpi_evaluate_object() is expected to return
> AE_NOT_FOUND.
>
> This said, if you think this case is unrealistic, why do you check for
> "status != AE_NOT_FOUND" at all?
>
> At this point maybe it would make more sense to simply drop this check
> and always bail out with the current error message.
>
> Basically a patch with the following only:
>
> - /* Fail if calling the method fails and ATIF is supported */
> - if (ACPI_FAILURE(status) && status != AE_NOT_FOUND) {
> + /* Fail if calling the method fails */
> + if (ACPI_FAILURE(status)) {
>
> This way we don't make a fuzz for a possibly unrealistic case, while
> still protecting against bugs and null-dereferences.
Yeah I think that's a good idea. Can you respin it as a v2?
>
>
> Regards,
>
>>
>> amdgpu_atif_pci_probe_handle() will check whether the handle is
>> available in the first place. We'll never this this far if that failed.
>>
>> Because of that I don't follow how this could return AE_NOT_FOUND.
>>> ---
>>> drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c | 11 +++++++----
>>> 1 file changed, 7 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c b/drivers/gpu/
>>> drm/amd/amdgpu/amdgpu_acpi.c
>>> index cce85389427f..f10c3261a4ab 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_acpi.c
>>> @@ -172,10 +172,13 @@ static union acpi_object
>>> *amdgpu_atif_call(struct amdgpu_atif *atif,
>>> &buffer);
>>> obj = (union acpi_object *)buffer.pointer;
>>> - /* 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));
>>> + /* Fail if calling the method fails */
>>> + if (ACPI_FAILURE(status)) {
>>> + if (status != AE_NOT_FOUND)
>>> + DRM_DEBUG_DRIVER("failed to evaluate ATIF got %s\n",
>>> + acpi_format_exception(status));
>>> + else
>>> + DRM_DEBUG_DRIVER("ATIF not supported\n");
>>> kfree(obj);
>>> return NULL;
>>> }
>>
>
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