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

HATAYAMA Daisuke
2013-03-05T07:05:09Z

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;
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));
+
+ /* - 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;
}