From 31d8526346b8737a4117bbc433d4b15788915771 Mon Sep 17 00:00:00 2001
From: Ben Gras <ben@minix3.org>
Date: Fri, 10 Aug 2012 18:27:23 +0200
Subject: [PATCH] libexec: add load_offset feature, used for ld.so

	. 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.
---
 lib/libexec/exec_elf.c | 14 +++++++-------
 lib/libexec/libexec.h  |  1 +
 servers/vfs/exec.c     |  5 +++++
 3 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/lib/libexec/exec_elf.c b/lib/libexec/exec_elf.c
index 3fc9f71c6..ab451a980 100644
--- a/lib/libexec/exec_elf.c
+++ b/lib/libexec/exec_elf.c
@@ -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;
diff --git a/lib/libexec/libexec.h b/lib/libexec/libexec.h
index 5169c4b21..69da9cb29 100644
--- a/lib/libexec/libexec.h
+++ b/lib/libexec/libexec.h
@@ -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 */
diff --git a/servers/vfs/exec.c b/servers/vfs/exec.c
index 2f6acb82e..cf49447bf 100644
--- a/servers/vfs/exec.c
+++ b/servers/vfs/exec.c
@@ -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);
 
-- 
2.44.0