Re: [PATCH v2 01/20] vmcore: refer to e_phoff member explicitly

Zhang Yanfei
2013-03-10T06:49:20Z

于 2013年03月05日 15:35, Zhang Yanfei 写道:
> 于 2013年03月02日 16:35, HATAYAMA Daisuke 写道:
>> Code around /proc/vmcore currently assumes program header table is
>> next to ELF header. But future change can break the assumption on
>> kexec-tools and the 1st kernel. To avoid worst case, now refer to
>> e_phoff member that indicates position of program header table in
>> file-offset.
>
> Reviewed-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
>
>>
>> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
>> ---
>>
>> fs/proc/vmcore.c | 40 ++++++++++++++++++++--------------------
>> 1 files changed, 20 insertions(+), 20 deletions(-)
>>
>> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
>> index b870f74..abf4f01 100644
>> --- a/fs/proc/vmcore.c
>> +++ b/fs/proc/vmcore.c
>> @@ -221,8 +221,8 @@ static u64 __init get_vmcore_size_elf64(char *elfptr)
>> Elf64_Phdr *phdr_ptr;
>>
>> ehdr_ptr = (Elf64_Ehdr *)elfptr;
>> - phdr_ptr = (Elf64_Phdr*)(elfptr + sizeof(Elf64_Ehdr));
>> - size = sizeof(Elf64_Ehdr) + ((ehdr_ptr->e_phnum) * sizeof(Elf64_Phdr));
>> + phdr_ptr = (Elf64_Phdr*)(elfptr + ehdr_ptr->e_phoff);
>> + size = ehdr_ptr->e_phoff + ((ehdr_ptr->e_phnum) * sizeof(Elf64_Phdr));
>> for (i = 0; i < ehdr_ptr->e_phnum; i++) {
>> size += phdr_ptr->p_memsz;
>> phdr_ptr++;
>> @@ -238,8 +238,8 @@ static u64 __init get_vmcore_size_elf32(char *elfptr)
>> Elf32_Phdr *phdr_ptr;
>>
>> ehdr_ptr = (Elf32_Ehdr *)elfptr;
>> - phdr_ptr = (Elf32_Phdr*)(elfptr + sizeof(Elf32_Ehdr));
>> - size = sizeof(Elf32_Ehdr) + ((ehdr_ptr->e_phnum) * sizeof(Elf32_Phdr));
>> + phdr_ptr = (Elf32_Phdr*)(elfptr + ehdr_ptr->e_phoff);
>> + size = ehdr_ptr->e_phoff + ((ehdr_ptr->e_phnum) * sizeof(Elf32_Phdr));
>> for (i = 0; i < ehdr_ptr->e_phnum; i++) {
>> size += phdr_ptr->p_memsz;
>> phdr_ptr++;
>> @@ -259,7 +259,7 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
>> u64 phdr_sz = 0, note_off;
>>
>> ehdr_ptr = (Elf64_Ehdr *)elfptr;
>> - phdr_ptr = (Elf64_Phdr*)(elfptr + sizeof(Elf64_Ehdr));
>> + phdr_ptr = (Elf64_Phdr*)(elfptr + ehdr_ptr->e_phoff);
>> for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
>> int j;
>> void *notes_section;
>> @@ -305,7 +305,7 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
>> /* Prepare merged PT_NOTE program header. */
>> phdr.p_type = PT_NOTE;
>> phdr.p_flags = 0;
>> - note_off = sizeof(Elf64_Ehdr) +
>> + note_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum - nr_ptnote +1) * sizeof(Elf64_Phdr);
>> phdr.p_offset = note_off;
>> phdr.p_vaddr = phdr.p_paddr = 0;
>> @@ -313,14 +313,14 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
>> phdr.p_align = 0;
>>
>> /* Add merged PT_NOTE program header*/
>> - tmp = elfptr + sizeof(Elf64_Ehdr);
>> + tmp = elfptr + ehdr_ptr->e_phoff;
>> 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)));
>> + memmove(tmp, tmp+i, ((*elfsz)-ehdr_ptr->e_phoff-sizeof(Elf64_Phdr)));
>>
>> /* Modify e_phnum to reflect merged headers. */
>> ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
>> @@ -340,7 +340,7 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
>> u64 phdr_sz = 0, note_off;
>>
>> ehdr_ptr = (Elf32_Ehdr *)elfptr;
>> - phdr_ptr = (Elf32_Phdr*)(elfptr + sizeof(Elf32_Ehdr));
>> + phdr_ptr = (Elf32_Phdr*)(elfptr + ehdr_ptr->e_phoff);
>> for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
>> int j;
>> void *notes_section;
>> @@ -386,7 +386,7 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
>> /* Prepare merged PT_NOTE program header. */
>> phdr.p_type = PT_NOTE;
>> phdr.p_flags = 0;
>> - note_off = sizeof(Elf32_Ehdr) +
>> + note_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum - nr_ptnote +1) * sizeof(Elf32_Phdr);
>> phdr.p_offset = note_off;
>> phdr.p_vaddr = phdr.p_paddr = 0;
>> @@ -394,14 +394,14 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
>> phdr.p_align = 0;
>>
>> /* Add merged PT_NOTE program header*/
>> - tmp = elfptr + sizeof(Elf32_Ehdr);
>> + tmp = elfptr + ehdr_ptr->e_phoff;
>> memcpy(tmp, &phdr, sizeof(phdr));
>> tmp += sizeof(phdr);
>>
>> /* Remove unwanted PT_NOTE program headers. */
>> i = (nr_ptnote - 1) * sizeof(Elf32_Phdr);
>> *elfsz = *elfsz - i;
>> - memmove(tmp, tmp+i, ((*elfsz)-sizeof(Elf32_Ehdr)-sizeof(Elf32_Phdr)));
>> + memmove(tmp, tmp+i, ((*elfsz)-ehdr_ptr->e_phoff-sizeof(Elf32_Phdr)));
>>
>> /* Modify e_phnum to reflect merged headers. */
>> ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
>> @@ -422,10 +422,10 @@ static int __init process_ptload_program_headers_elf64(char *elfptr,
>> struct vmcore *new;
>>
>> ehdr_ptr = (Elf64_Ehdr *)elfptr;
>> - phdr_ptr = (Elf64_Phdr*)(elfptr + sizeof(Elf64_Ehdr)); /* PT_NOTE hdr */
>> + phdr_ptr = (Elf64_Phdr*)(elfptr + ehdr_ptr->e_phoff); /* PT_NOTE hdr */
>>
>> /* First program header is PT_NOTE header. */
>> - vmcore_off = sizeof(Elf64_Ehdr) +
>> + vmcore_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum) * sizeof(Elf64_Phdr) +
>> phdr_ptr->p_memsz; /* Note sections */
>>
>> @@ -459,10 +459,10 @@ static int __init process_ptload_program_headers_elf32(char *elfptr,
>> struct vmcore *new;
>>
>> ehdr_ptr = (Elf32_Ehdr *)elfptr;
>> - phdr_ptr = (Elf32_Phdr*)(elfptr + sizeof(Elf32_Ehdr)); /* PT_NOTE hdr */
>> + phdr_ptr = (Elf32_Phdr*)(elfptr + ehdr_ptr->e_phoff); /* PT_NOTE hdr */
>>
>> /* First program header is PT_NOTE header. */
>> - vmcore_off = sizeof(Elf32_Ehdr) +
>> + vmcore_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum) * sizeof(Elf32_Phdr) +
>> phdr_ptr->p_memsz; /* Note sections */
>>
>> @@ -496,7 +496,7 @@ static void __init set_vmcore_list_offsets_elf64(char *elfptr,
>> ehdr_ptr = (Elf64_Ehdr *)elfptr;
>>
>> /* Skip Elf header and program headers. */
>> - vmcore_off = sizeof(Elf64_Ehdr) +
>> + vmcore_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum) * sizeof(Elf64_Phdr);
>>
>> list_for_each_entry(m, vc_list, list) {
>> @@ -516,7 +516,7 @@ static void __init set_vmcore_list_offsets_elf32(char *elfptr,
>> ehdr_ptr = (Elf32_Ehdr *)elfptr;
>>
>> /* Skip Elf header and program headers. */
>> - vmcore_off = sizeof(Elf32_Ehdr) +
>> + vmcore_off = ehdr_ptr->e_phoff +
>> (ehdr_ptr->e_phnum) * sizeof(Elf32_Phdr);
>>
>> list_for_each_entry(m, vc_list, list) {
>> @@ -553,7 +553,7 @@ static int __init parse_crash_elf64_headers(void)
>> }
>>
>> /* Read in all elf headers. */
>> - elfcorebuf_sz = sizeof(Elf64_Ehdr) + ehdr.e_phnum * sizeof(Elf64_Phdr);
>> + elfcorebuf_sz = ehdr.e_phoff + ehdr.e_phnum * sizeof(Elf64_Phdr);

One minor suggestion.

Previously, when the code assumes program headers are following immediately
the ELF header, it uses

elfcorebuf_sz = sizeof(Elf64_Ehdr) + ehdr.e_phnum * sizeof(Elf64_Phdr);

to calculate the size of ELF header and ELF program headers

This patch avoids the assumption, and uses ehdr.e_phoff to get the program
headers' address. But it will read unrelated contents into elfcorebuf if
program headers are not following immediately the ELF header. So could the
code be:

elfcorebuf_sz = sizeof(Elf64_Ehdr) + ehdr.e_phnum * sizeof(Elf64_Phdr);
addr = elfcorehdr_addr + ehdr.e_phoff;
memcpy(elfcorebuf, &ehdr, sizeof(Elf64_Ehdr));
read_from_oldmem(elfcorebuf + sizeof(Elf64_Ehdr), elfcorebuf_sz -
sizeof(Elf64_Ehdr), &addr, 0);
(Elf64_Ehdr *)elfcorebuf->e_phoff = sizeof(Elf64_Ehdr);

>> elfcorebuf = kmalloc(elfcorebuf_sz, GFP_KERNEL);
>> if (!elfcorebuf)
>> return -ENOMEM;
>> @@ -608,7 +608,7 @@ static int __init parse_crash_elf32_headers(void)
>> }
>>
>> /* Read in all elf headers. */
>> - elfcorebuf_sz = sizeof(Elf32_Ehdr) + ehdr.e_phnum * sizeof(Elf32_Phdr);
>> + elfcorebuf_sz = ehdr.e_phoff + ehdr.e_phnum * sizeof(Elf32_Phdr);
>> elfcorebuf = kmalloc(elfcorebuf_sz, GFP_KERNEL);
>> if (!elfcorebuf)
>> return -ENOMEM;
>>
>>
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>>
>
>
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