From: Vivek Goyal <vgoyal@xxxxxxxxxx> 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 at jp.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
