linux-kernel - Re: [PATCH v9 05/11] arm64: kexec_file: load initrd and device-tree

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Date:   Fri, 18 May 2018 16:59:13 +0100
From:   James Morse <james.morse@....com>
To:     AKASHI Takahiro <takahiro.akashi@...aro.org>
Cc:     catalin.marinas@....com, will.deacon@....com, dhowells@...hat.com,
        vgoyal@...hat.com, herbert@...dor.apana.org.au,
        davem@...emloft.net, dyoung@...hat.com, bhe@...hat.com,
        arnd@...db.de, ard.biesheuvel@...aro.org, bhsharma@...hat.com,
        kexec@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v9 05/11] arm64: kexec_file: load initrd and device-tree

Hi Akashi,

On 18/05/18 08:42, AKASHI Takahiro wrote:
> On Fri, May 18, 2018 at 04:11:35PM +0900, AKASHI Takahiro wrote:
>> On Tue, May 15, 2018 at 05:20:00PM +0100, James Morse wrote:
>>> On 25/04/18 07:26, AKASHI Takahiro wrote:
>>>> diff --git a/arch/arm64/kernel/machine_kexec_file.c b/arch/arm64/kernel/machine_kexec_file.c
>>>> index f9ebf54ca247..b3b9b1725d8a 100644
>>>> --- a/arch/arm64/kernel/machine_kexec_file.c
>>>> +++ b/arch/arm64/kernel/machine_kexec_file.c

>>>> @@ -55,3 +74,144 @@ int arch_kexec_walk_mem(struct kexec_buf *kbuf,

>>>> +	buf = vmalloc(buf_size);
>>>> +	if (!buf) {
>>>> +		ret = -ENOMEM;
>>>> +		goto out_err;
>>>> +	}
>>>> +
>>>> +	ret = fdt_open_into(initial_boot_params, buf, buf_size);
>>>> +	if (ret)
>>>> +		goto out_err;
>>>> +
>>>> +	nodeoffset = fdt_path_offset(buf, "/chosen");
>>>> +	if (nodeoffset < 0)
>>>> +		goto out_err;
>>>> +
>>>> +	/* add bootargs */
>>>> +	if (cmdline) {
>>>> +		ret = fdt_setprop(buf, nodeoffset, "bootargs",
>>>> +						cmdline, cmdline_len + 1);
>>>
>>> fdt_setprop_string()?
>>
>> OK
> 
> cmdline_len is passed by system call, kexec_file_load(), and this means
> that we can't believe that cmdline is always terminated with '\0'.

Yuck, we expect user-space to tell us how long the string is. It may be worth a
comment that it isn't necessarily null-terminated, as that is surprising!

(I assume the DT's property length is enough to make that safe for the new
kernel to read).


>>>> +		/* within 1GB-aligned window of up to 32GB in size */
>>>> +		kbuf.buf_max = round_down(kern_seg->mem, SZ_1G)
>>>> +						+ (unsigned long)SZ_1G * 32;
>>>> +		kbuf.top_down = false;
>>>> +
>>>> +		ret = kexec_add_buffer(&kbuf);
>>>> +		if (ret)
>>>> +			goto out_err;
>>>> +		initrd_load_addr = kbuf.mem;
>>>> +
>>>> +		pr_debug("Loaded initrd at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
>>>> +				initrd_load_addr, initrd_len, initrd_len);
>>>> +	}
>>>> +
>>>> +	/* load dtb blob */
>>>> +	ret = setup_dtb(image, initrd_load_addr, initrd_len,
>>>> +				cmdline, cmdline_len, &dtb, &dtb_len);
>>>> +	if (ret) {
>>>> +		pr_err("Preparing for new dtb failed\n");
>>>> +		goto out_err;
>>>> +	}
>>>> +
>>>> +	kbuf.buffer = dtb;
>>>> +	kbuf.bufsz = dtb_len;
>>>> +	kbuf.memsz = dtb_len;
>>>> +	/* not across 2MB boundary */
>>>> +	kbuf.buf_align = SZ_2M;
>>>> +	kbuf.buf_max = ULONG_MAX;
>>>> +	kbuf.top_down = true;
>>>> +
>>>> +	ret = kexec_add_buffer(&kbuf);
>>>> +	if (ret)
>>>> +		goto out_err;
>>>> +	image->arch.dtb_mem = kbuf.mem;
>>>> +	image->arch.dtb_buf = dtb;
>>>> +
>>>> +	pr_debug("Loaded dtb at 0x%lx bufsz=0x%lx memsz=0x%lx\n",
>>>> +			kbuf.mem, dtb_len, dtb_len);
>>>> +
>>>> +	return 0;
>>>> +
>>>> +out_err:
>>>> +	vfree(dtb);
>>>> +	image->arch.dtb_buf = NULL;
>>>
>>> Won't kimage_file_post_load_cleanup() always be called if we return an error
>>> here? Why not leave the free()ing until then?
>>
>> Right.
>> The reason why I left the code here was that we'd better locally clean up
>> all the stuff that were locally allocated if we trivially need to (and can)
>> do so.
>>
>> As it's redundant, I will remove it.
> 
> will remove only "image->arch.dtb_buf = NULL."

Ah, because you haven't set the arch.dtb_buf pointer yet.

What about in patch 7 where you expect kimage_file_prepare_segments() to call
arch_kimage_file_post_load_cleanup() to free the arch.elf_headers? I'd expect
the free()ing to always happen in one place.


Thanks,

James