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libexec: add load_offset feature, used for ld.so

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. ld.so is linked at 0 but it can relocate itself; we
	  wish to load ld.so higher though to trap NULL dereferences.
	  if we know we have to execute ld.so, vfs tells libexec to put it
	  higher.
This commit is contained in:
Ben Gras 2012-08-10 18:27:23 +02:00
parent ad898517ac
commit 31d8526346
3 changed files with 13 additions and 7 deletions
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14
lib/libexec/exec_elf.c
View file

@ -159,11 +159,11 @@ int libexec_load_elf(struct exec_info *execi)
if(execi->clearproc) execi->clearproc(execi);
for (i = 0; i < hdr->e_phnum; i++) {
vir_bytes seg_membytes, page_offset, vaddr;
vir_bytes seg_membytes, page_offset, p_vaddr, vaddr;
vir_bytes chunk, vfileend, vmemend;
Elf_Phdr *ph = &phdr[i];
if (ph->p_type != PT_LOAD || ph->p_memsz == 0) continue;
vaddr = ph->p_vaddr;
vaddr = p_vaddr = ph->p_vaddr + execi->load_offset;
seg_membytes = ph->p_memsz;
page_offset = vaddr % PAGE_SIZE;
vaddr -= page_offset;
@ -183,19 +183,19 @@ int libexec_load_elf(struct exec_info *execi)
#endif
/* Copy executable section into it */
if(execi->copymem(execi, ph->p_offset, ph->p_vaddr, ph->p_filesz) != OK) {
if(execi->copymem(execi, ph->p_offset, p_vaddr, ph->p_filesz) != OK) {
if(execi->clearproc) execi->clearproc(execi);
return ENOMEM;
}
#if ELF_DEBUG
printf("copied 0x%lx-0x%lx\n", ph->p_vaddr, ph->p_vaddr+ph->p_filesz);
printf("copied 0x%lx-0x%lx\n", p_vaddr, p_vaddr+ph->p_filesz);
#endif
/* Clear remaining bits */
vfileend = ph->p_vaddr + ph->p_filesz;
vfileend = p_vaddr + ph->p_filesz;
vmemend = vaddr + seg_membytes;
if((chunk = ph->p_vaddr - vaddr) > 0) {
if((chunk = p_vaddr - vaddr) > 0) {
#if ELF_DEBUG
printf("start clearing 0x%lx-0x%lx\n", vaddr, vaddr+chunk);
#endif
@ -220,7 +220,7 @@ int libexec_load_elf(struct exec_info *execi)
#endif
/* record entry point and lowest load vaddr for caller */
execi->pc = hdr->e_entry;
execi->pc = hdr->e_entry + execi->load_offset;
execi->load_base = startv;
return OK;

1
lib/libexec/libexec.h
View file

@ -27,6 +27,7 @@ struct exec_info {
gid_t new_gid; /* Process GID after exec */
int allow_setuid; /* Allow set{u,g}id execution? */
vir_bytes stack_size; /* Desired stack size */
vir_bytes load_offset; /* Desired load offset */
/* Callback pointers for use by libexec */
libexec_loadfunc_t copymem; /* Copy callback */

5
servers/vfs/exec.c
View file

@ -286,6 +286,11 @@ int pm_exec(endpoint_t proc_e, vir_bytes path, size_t path_len,
FAILCHECK(r);
}
/* ld.so is linked at 0, but it can relocate itself; we
* want it higher to trap NULL pointer dereferences.
*/
execi.args.load_offset = 0x10000;
/* Remember it */
strlcpy(execi.execname, finalexec, PATH_MAX);