From: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
To: Rob Herring <robh@kernel.org>
Cc: devicetree@vger.kernel.org, kbuild-all@lists.01.org,
kbuild test robot <lkp@intel.com>,
Thiago Jung Bauermann <bauerman@linux.ibm.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Dan Carpenter <dan.carpenter@oracle.com>,
Daniel Axtens <dja@axtens.net>
Subject: Re: [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load()
Date: Tue, 20 Apr 2021 07:42:10 -0700 [thread overview]
Message-ID: <2e8dd39b-0372-4874-340e-6f87185091cc@linux.microsoft.com> (raw)
In-Reply-To: <CAL_JsqLS9Wu_+_S-2wwMb3Chd_8RYAtFe_uLh5tjj_sAkTgRJA@mail.gmail.com>
On 4/20/21 6:06 AM, Rob Herring wrote:
> On Tue, Apr 20, 2021 at 12:20 AM Lakshmi Ramasubramanian
> <nramas@linux.microsoft.com> wrote:
>>
>> On 4/19/21 10:00 PM, Dan Carpenter wrote:
>>> On Tue, Apr 20, 2021 at 09:30:16AM +1000, Michael Ellerman wrote:
>>>> Lakshmi Ramasubramanian <nramas@linux.microsoft.com> writes:
>>>>> On 4/16/21 2:05 AM, Michael Ellerman wrote:
>>>>>
>>>>>> Daniel Axtens <dja@axtens.net> writes:
>>>>>>>> On 4/15/21 12:14 PM, Lakshmi Ramasubramanian wrote:
>>>>>>>>
>>>>>>>> Sorry - missed copying device-tree and powerpc mailing lists.
>>>>>>>>
>>>>>>>>> There are a few "goto out;" statements before the local variable "fdt"
>>>>>>>>> is initialized through the call to of_kexec_alloc_and_setup_fdt() in
>>>>>>>>> elf64_load(). This will result in an uninitialized "fdt" being passed
>>>>>>>>> to kvfree() in this function if there is an error before the call to
>>>>>>>>> of_kexec_alloc_and_setup_fdt().
>>>>>>>>>
>>>>>>>>> Initialize the local variable "fdt" to NULL.
>>>>>>>>>
>>>>>>> I'm a huge fan of initialising local variables! But I'm struggling to
>>>>>>> find the code path that will lead to an uninit fdt being returned...
>>>>>>>
>>>>>>> The out label reads in part:
>>>>>>>
>>>>>>> /* Make kimage_file_post_load_cleanup free the fdt buffer for us. */
>>>>>>> return ret ? ERR_PTR(ret) : fdt;
>>>>>>>
>>>>>>> As far as I can tell, any time we get a non-zero ret, we're going to
>>>>>>> return an error pointer rather than the uninitialised value...
>>>>>
>>>>> As Dan pointed out, the new code is in linux-next.
>>>>>
>>>>> I have copied the new one below - the function doesn't return fdt, but
>>>>> instead sets it in the arch specific field (please see the link to the
>>>>> updated elf_64.c below).
>>>>>
>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/robh/linux.git/tree/arch/powerpc/kexec/elf_64.c?h=for-next
>>>>>
>>>>>>>
>>>>>>> (btw, it does look like we might leak fdt if we have an error after we
>>>>>>> successfully kmalloc it.)
>>>>>>>
>>>>>>> Am I missing something? Can you link to the report for the kernel test
>>>>>>> robot or from Dan?
>>>>>
>>>>> /*
>>>>> * Once FDT buffer has been successfully passed to
>>>>> kexec_add_buffer(),
>>>>> * the FDT buffer address is saved in image->arch.fdt. In that
>>>>> case,
>>>>> * the memory cannot be freed here in case of any other error.
>>>>> */
>>>>> if (ret && !image->arch.fdt)
>>>>> kvfree(fdt);
>>>>>
>>>>> return ret ? ERR_PTR(ret) : NULL;
>>>>>
>>>>> In case of an error, the memory allocated for fdt is freed unless it has
>>>>> already been passed to kexec_add_buffer().
>>>>
>>>> It feels like the root of the problem is that the kvfree of fdt is in
>>>> the wrong place. It's only allocated later in the function, so the error
>>>> path should reflect that. Something like the patch below.
>>>>
>>>> cheers
>>>>
>>>>
>>>> diff --git a/arch/powerpc/kexec/elf_64.c b/arch/powerpc/kexec/elf_64.c
>>>> index 5a569bb51349..02662e72c53d 100644
>>>> --- a/arch/powerpc/kexec/elf_64.c
>>>> +++ b/arch/powerpc/kexec/elf_64.c
>>>> @@ -114,7 +114,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>>>> ret = setup_new_fdt_ppc64(image, fdt, initrd_load_addr,
>>>> initrd_len, cmdline);
>>>> if (ret)
>>>> - goto out;
>>>> + goto out_free_fdt;
>>>>
>>>> fdt_pack(fdt);
>>>>
>>>> @@ -125,7 +125,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>>>> kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
>>>> ret = kexec_add_buffer(&kbuf);
>>>> if (ret)
>>>> - goto out;
>>>> + goto out_free_fdt;
>>>>
>>>> /* FDT will be freed in arch_kimage_file_post_load_cleanup */
>>>> image->arch.fdt = fdt;
>>>> @@ -140,18 +140,14 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
>>>> if (ret)
>>>> pr_err("Error setting up the purgatory.\n");
>>>>
>>>> + goto out;
>>>
>>> This will leak. It would need to be something like:
>>>
>>> if (ret) {
>>> pr_err("Error setting up the purgatory.\n");
>>> goto out_free_fdt;
>>> }
>> Once "fdt" buffer is successfully passed to kexec_add_buffer() it cannot
>> be freed here - it will be freed when the kexec cleanup function is called.
>
> That may be the case currently, but really if a function returns an
> error it should have undone anything it did like memory allocations. I
> don't think you should do that to fix this issue, but it would be a
> good clean-up.
>
I agree - in case of an error the function should do a proper clean-up.
Just to be clear - for now, I will leave this as is. Correct?
In my patch, I will do the following changes:
=> Free "fdt" when possible (as Michael had suggested in his patch)
=> Zero out "elf_info" struct at the start of the function.
thanks,
-lakshmi
next prev parent reply other threads:[~2021-04-20 14:42 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20210415191437.20212-1-nramas@linux.microsoft.com>
2021-04-15 19:18 ` [PATCH] powerpc: Initialize local variable fdt to NULL in elf64_load() Lakshmi Ramasubramanian
2021-04-16 6:44 ` Daniel Axtens
2021-04-16 7:00 ` Christophe Leroy
2021-04-16 8:09 ` Dan Carpenter
2021-04-16 12:19 ` Michael Ellerman
2021-04-16 7:40 ` Dan Carpenter
2021-04-16 9:05 ` Michael Ellerman
2021-04-16 14:37 ` Lakshmi Ramasubramanian
2021-04-19 23:30 ` Michael Ellerman
2021-04-20 1:33 ` Lakshmi Ramasubramanian
2021-04-20 5:00 ` Dan Carpenter
2021-04-20 5:20 ` Lakshmi Ramasubramanian
2021-04-20 13:06 ` Rob Herring
2021-04-20 14:42 ` Lakshmi Ramasubramanian [this message]
2021-04-20 15:04 ` Lakshmi Ramasubramanian
2021-04-20 15:47 ` Rob Herring
2021-04-20 15:55 ` Lakshmi Ramasubramanian
2021-04-22 2:21 ` Daniel Axtens
2021-04-22 8:05 ` David Laight
2021-04-22 9:34 ` Dan Carpenter
2021-04-22 16:54 ` Segher Boessenkool
2021-04-23 13:50 ` Michael Ellerman
2021-04-23 14:42 ` David Laight
2021-04-23 15:11 ` Rob Herring
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