linux-kernel - Re: [PATCH 02/13] vmcore: round up buffer size of ELF headers by PAGE

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Message-Id: <20130219.005856.267479651.d.hatayama@jp.fujitsu.com>
Date:	Tue, 19 Feb 2013 00:58:56 +0900 (JST)
From:	HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
To:	vgoyal@...hat.com
Cc:	ebiederm@...ssion.com, cpw@....com,
	kumagai-atsushi@....nes.nec.co.jp, lisa.mitchell@...com,
	kexec@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/13] vmcore: round up buffer size of ELF headers by
 PAGE_SIZE

From: Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [PATCH 02/13] vmcore: round up buffer size of ELF headers by PAGE_SIZE
Date: Fri, 15 Feb 2013 10:18:21 -0500

> On Thu, Feb 14, 2013 at 07:11:54PM +0900, HATAYAMA Daisuke wrote:
>> To satisfy mmap() page-size boundary requirement, reound up buffer
>> size of ELF headers by PAGE_SIZE. The resulting value becomes offset
>> of ELF note segments and it's assigned in unique PT_NOTE program
>> header entry.
>> 
>> Also, some part that assumes past ELF headers' size is replaced by
>> this new rounded-up value.
>> 
>> Signed-off-by: HATAYAMA Daisuke <d.hatayama@...fujitsu.com>
>> ---
>> 
>>  fs/proc/vmcore.c |    9 +++++----
>>  1 files changed, 5 insertions(+), 4 deletions(-)
>> 
>> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
>> index 85714c3..5010ead 100644
>> --- a/fs/proc/vmcore.c
>> +++ b/fs/proc/vmcore.c
>> @@ -313,7 +313,7 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
>>  	phdr.p_flags   = 0;
>>  	note_off = sizeof(Elf64_Ehdr) +
>>  			(ehdr_ptr->e_phnum - nr_ptnote +1) * sizeof(Elf64_Phdr);
>> -	phdr.p_offset  = note_off;
>> +	phdr.p_offset  = roundup(note_off, PAGE_SIZE);
>>  	phdr.p_vaddr   = phdr.p_paddr = 0;
>>  	phdr.p_filesz  = phdr.p_memsz = phdr_sz;
>>  	phdr.p_align   = 0;
>> @@ -331,6 +331,8 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
>>  	/* Modify e_phnum to reflect merged headers. */
>>  	ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
>>  
> 
> Hi Hatayama,
> 
> While reading the /proc/vmcore code again, I realized that we are making
> a horrible assumption. And that is that all PT_NOTE program headers
> prepared by kexec-tools are contiguous. And we also seem to be assuming
> that all PT_NOTE phdrs are following immediately Elf Header.
> 
>         /* Add merged PT_NOTE program header*/
>         tmp = elfptr + sizeof(Elf64_Ehdr);
>         memcpy(tmp, &phdr, sizeof(phdr));
>         tmp += sizeof(phdr);
> 
>         /* Remove unwanted PT_NOTE program headers. */
>         i = (nr_ptnote - 1) * sizeof(Elf64_Phdr);
>         *elfsz = *elfsz - i;
>         memmove(tmp, tmp+i, ((*elfsz)-sizeof(Elf64_Ehdr)-sizeof(Elf64_Phdr)));
> 
> I know I wrote this code but now I realize that this is very bad
> assumption. We should not be assuming where PT_NOTE headers are and
> also should not be assuming that these are contiguous.
> 
> This will require fixing. I think we just need to read old elf headers
> in a buffer and prepare new headers (merged one) in a separate buffer
> instead of trying to make do with single buffer.
> 
> If it is not too much of trouble, can you please do this cleanup and
> rebase your patches on top of it.
> 
> Thanks
> Vivek

Yes, I'll do this.

Thanks.
HATAYAMA, Daisuke

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