Re: [PATCH v2 02/20] vmcore: rearrange program headers without assuming consequtive PT_NOTE entries

Zhang Yanfei
2013-03-05T08:38:54Z

于 2013年03月02日 16:35, HATAYAMA Daisuke 写道:
> Current code assumes all PT_NOTE headers are placed at the beginning
> of program header table and they are consequtive. But the assumption
> could be broken by future changes on either kexec-tools or the 1st
> kernel. This patch removes the assumption and rearranges program
> headers as the following conditions are satisfied:
>
> - PT_NOTE entry is unique at the first entry,
>
> - the order of program headers are unchanged during this
> rearrangement, only their positions are changed in positive
> direction.
>
> - unused part that occurs in the bottom of program headers are filled
> with 0.
>
> Also, this patch adds one exceptional case where the number of PT_NOTE
> entries is somehow 0. Then, immediately go out of the function.
>
> Signed-off-by: HATAYAMA Daisuke <d.hatayama@jp.fujitsu.com>
> ---
>
> fs/proc/vmcore.c | 92 +++++++++++++++++++++++++++++++++++++++++++-----------
> 1 files changed, 74 insertions(+), 18 deletions(-)
>
> diff --git a/fs/proc/vmcore.c b/fs/proc/vmcore.c
> index abf4f01..b5c9e33 100644
> --- a/fs/proc/vmcore.c
> +++ b/fs/proc/vmcore.c
> @@ -251,8 +251,7 @@ static u64 __init get_vmcore_size_elf32(char *elfptr)
> static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
> struct list_head *vc_list)
> {
> - int i, nr_ptnote=0, rc=0;
> - char *tmp;
> + int i, j, nr_ptnote=0, i_ptnote, rc=0;

After applying the patch, there are two "j" defined.

251 static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
252 struct list_head *vc_list)
253 {
254 int i, j, nr_ptnote=0, i_ptnote, rc=0;
255 Elf64_Ehdr *ehdr_ptr;
256 Elf64_Phdr phdr, *phdr_ptr;
257 Elf64_Nhdr *nhdr_ptr;
258 u64 phdr_sz = 0, note_off;
259
260 ehdr_ptr = (Elf64_Ehdr *)elfptr;
261 phdr_ptr = (Elf64_Phdr*)(elfptr + ehdr_ptr->e_phoff);
262 for (i = 0; i < ehdr_ptr->e_phnum; i++, phdr_ptr++) {
263 int j;
264 void *notes_section;
265 struct vmcore *new;

line 254 and 263.

> Elf64_Ehdr *ehdr_ptr;
> Elf64_Phdr phdr, *phdr_ptr;
> Elf64_Nhdr *nhdr_ptr;
> @@ -302,6 +301,39 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
> kfree(notes_section);
> }
>
> + if (nr_ptnote == 0)
> + goto out;
> +
> + phdr_ptr = (Elf64_Phdr *)(elfptr + ehdr_ptr->e_phoff);
> +
> + /* Remove unwanted PT_NOTE program headers. */
> +
> + /* - 1st pass shifts non-PT_NOTE entries until the first
> + PT_NOTE entry. */
> + i_ptnote = -1;
> + for (i = 0; i < ehdr_ptr->e_phnum; ++i) {
> + if (phdr_ptr[i].p_type == PT_NOTE) {
> + i_ptnote = i;
> + break;
> + }
> + }
> + BUG_ON(i_ptnote == -1); /* impossible case since nr_ptnote > 0. */
> + memmove(phdr_ptr + 1, phdr_ptr, i_ptnote * sizeof(Elf64_Phdr));

is there any problem with this move? What is the batch bytes for every loop
of memmove?

if i_ptnode == 2, so we have

-------------------------------------
| PT_LOAD 1 | PT_LOAD 2 | PT_NOTE 1 |
-------------------------------------

-->

-------------------------------------
| | PT_LOAD 1 | PT_LOAD 2 |
-------------------------------------

right? In the move, Does PT_LOAD 1 overwrite the original PT_LOAD 2?

> +
> + /* - 2nd pass moves the remaining non-PT_NOTE entries under
> + the first PT_NOTE entry. */
> + for (i = j = i_ptnote + 1; i < ehdr_ptr->e_phnum; i++) {
> + if (phdr_ptr[i].p_type != PT_NOTE) {
> + memmove(phdr_ptr + j, phdr_ptr + i,
> + sizeof(Elf64_Phdr));
> + j++;
> + }
> + }
> +
> + /* - Finally, fill unused part with 0. */
> + memset(phdr_ptr + ehdr_ptr->e_phnum - (nr_ptnote - 1), 0,
> + (nr_ptnote - 1) * sizeof(Elf64_Phdr));
> +
> /* Prepare merged PT_NOTE program header. */
> phdr.p_type = PT_NOTE;
> phdr.p_flags = 0;
> @@ -313,18 +345,14 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
> phdr.p_align = 0;
>
> /* Add merged PT_NOTE program header*/
> - tmp = elfptr + ehdr_ptr->e_phoff;
> - memcpy(tmp, &phdr, sizeof(phdr));
> - tmp += sizeof(phdr);
> + memcpy(phdr_ptr, &phdr, sizeof(Elf64_Phdr));
>
> - /* Remove unwanted PT_NOTE program headers. */
> - i = (nr_ptnote - 1) * sizeof(Elf64_Phdr);
> - *elfsz = *elfsz - i;
> - memmove(tmp, tmp+i, ((*elfsz)-ehdr_ptr->e_phoff-sizeof(Elf64_Phdr)));
> + *elfsz = *elfsz - (nr_ptnote - 1) * sizeof(Elf64_Phdr);
>
> /* Modify e_phnum to reflect merged headers. */
> ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
>
> +out:
> return 0;
> }
>
> @@ -332,8 +360,7 @@ static int __init merge_note_headers_elf64(char *elfptr, size_t *elfsz,
> static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
> struct list_head *vc_list)
> {
> - int i, nr_ptnote=0, rc=0;
> - char *tmp;
> + int i, j, nr_ptnote=0, i_ptnote, rc=0;
> Elf32_Ehdr *ehdr_ptr;
> Elf32_Phdr phdr, *phdr_ptr;
> Elf32_Nhdr *nhdr_ptr;
> @@ -383,6 +410,39 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
> kfree(notes_section);
> }
>
> + if (nr_ptnote == 0)
> + goto out;
> +
> + phdr_ptr = (Elf32_Phdr *)(elfptr + ehdr_ptr->e_phoff);
> +
> + /* Remove unwanted PT_NOTE program headers. */
> +
> + /* - 1st pass shifts non-PT_NOTE entries until the first
> + PT_NOTE entry. */
> + i_ptnote = -1;
> + for (i = 0; i < ehdr_ptr->e_phnum; ++i) {
> + if (phdr_ptr[i].p_type == PT_NOTE) {
> + i_ptnote = i;
> + break;
> + }
> + }
> + BUG_ON(i_ptnote == -1); /* impossible case since nr_ptnote > 0. */
> + memmove(phdr_ptr + 1, phdr_ptr, i_ptnote * sizeof(Elf32_Phdr));
> +
> + /* - 2nd pass moves the remaining non-PT_NOTE entries under
> + the first PT_NOTE entry. */
> + for (i = j = i_ptnote + 1; i < ehdr_ptr->e_phnum; i++) {
> + if (phdr_ptr[i].p_type != PT_NOTE) {
> + memmove(phdr_ptr + j, phdr_ptr + i,
> + sizeof(Elf32_Phdr));
> + j++;
> + }
> + }
> +
> + /* - Finally, fill unused part with 0. */
> + memset(phdr_ptr + ehdr_ptr->e_phnum - (nr_ptnote - 1), 0,
> + (nr_ptnote - 1) * sizeof(Elf32_Phdr));
> +
> /* Prepare merged PT_NOTE program header. */
> phdr.p_type = PT_NOTE;
> phdr.p_flags = 0;
> @@ -394,18 +454,14 @@ static int __init merge_note_headers_elf32(char *elfptr, size_t *elfsz,
> phdr.p_align = 0;
>
> /* Add merged PT_NOTE program header*/
> - tmp = elfptr + ehdr_ptr->e_phoff;
> - memcpy(tmp, &phdr, sizeof(phdr));
> - tmp += sizeof(phdr);
> + memcpy(phdr_ptr, &phdr, sizeof(Elf32_Phdr));
>
> - /* Remove unwanted PT_NOTE program headers. */
> - i = (nr_ptnote - 1) * sizeof(Elf32_Phdr);
> - *elfsz = *elfsz - i;
> - memmove(tmp, tmp+i, ((*elfsz)-ehdr_ptr->e_phoff-sizeof(Elf32_Phdr)));
> + *elfsz = *elfsz - (nr_ptnote - 1) * sizeof(Elf32_Phdr);
>
> /* Modify e_phnum to reflect merged headers. */
> ehdr_ptr->e_phnum = ehdr_ptr->e_phnum - nr_ptnote + 1;
>
> +out:
> return 0;
> }
>
>
>
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