Re: Non-Exec stack patches

From: Kurt Garloff
Date: Wed Mar 24 2004 - 05:56:35 EST

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Hi Andrew, Ingo,

On Tue, Mar 23, 2004 at 04:41:04PM -0800, Andrew Morton wrote:
> It gets rejects in arch/x86_64/ia32/ia32_binfmt.c and
> arch/ia64/ia32/binfmt_elf32.c - someone has been dinking with your
> put_dirty_page() prototype.

That's the anon_vma stuff from Andrea, which we have merged locally.
Sorry, I forgot that it touched these places.

> I dropped those bits.

Not a good idea, as stack protection won't work in ia32 emulation of
x86_64 and ia64 then.

I readded and did a clean diff against 2.6.5-rc2 and also integrated
your comments patch.

> And I added the missing bit:

Thx!

> Now, what should the kernel do if the executable requests EXSTACK_DISABLE_X
> but the kernel cannot do that? Is it not a bit misleading/dangerous to
> permit the executable to run anyway?

Yes. It has to ...
Otherwise, most binaries would not work in i386 any more :-/

Updated patch attached.
--
Kurt Garloff <garloff@xxxxxxx> Cologne, DE
SUSE LINUX AG, Nuernberg, DE SUSE Labs (Head)

From: Kurt Garloff <garloff@xxxxxxx>

A patch to parse the elf binaries for a PT_GNU_STACK section to set the
stack non-executable if possible. Most parts have been shamelessly stolen
from Ingo Molnar's more ambitious stackshield
http://people.redhat.com/mingo/exec-shield/exec-shield-2.6.4-C9

The toolchain has meanwhile support for marking the binaries with a
PT_GNU_STACK section wwithout x bit as needed.

If no such section is found, we leave the stack to whatever the arch
defaults to. If there is one, we explicitly disabled the VM_EXEC bit if no
x bit is found, otherwise explicitly enable.

---

arch/ia64/ia32/binfmt_elf32.c | 16 +++++++++++-----
arch/ia64/ia32/ia32priv.h | 2 +-
arch/mips/kernel/irixelf.c | 2 +-
arch/s390/kernel/binfmt_elf32.c | 4 ++--
arch/s390/kernel/compat_exec.c | 3 ++-
arch/sparc64/kernel/binfmt_aout32.c | 2 +-
arch/x86_64/ia32/ia32_aout.c | 4 ++--
arch/x86_64/ia32/ia32_binfmt.c | 15 ++++++++++-----
fs/binfmt_aout.c | 2 +-
fs/binfmt_elf.c | 12 +++++++++++-
fs/binfmt_som.c | 2 +-
fs/exec.c | 14 +++++++++++---
include/linux/binfmts.h | 8 +++++++-
include/linux/elf.h | 2 ++
14 files changed, 63 insertions(+), 25 deletions(-)

diff -uNrp linux-2.6.5-rc2/arch/ia64/ia32/binfmt_elf32.c linux-2.6.5-rc2.nonexecstack/arch/ia64/ia32/binfmt_elf32.c
--- linux-2.6.5-rc2/arch/ia64/ia32/binfmt_elf32.c 2004-03-11 03:55:44.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/ia64/ia32/binfmt_elf32.c 2004-03-24 11:43:50.000000000 +0100
@@ -35,7 +35,7 @@ extern void ia64_elf32_init (struct pt_r

static void elf32_set_personality (void);

-#define setup_arg_pages(bprm) ia32_setup_arg_pages(bprm)
+#define setup_arg_pages(bprm,exec) ia32_setup_arg_pages(bprm,exec)
#define elf_map elf32_map

#undef SET_PERSONALITY
@@ -149,7 +149,7 @@ ia64_elf32_init (struct pt_regs *regs)
}

int
-ia32_setup_arg_pages (struct linux_binprm *bprm)
+ia32_setup_arg_pages (struct linux_binprm *bprm, int executable_stack)
{
unsigned long stack_base;
struct vm_area_struct *mpnt;
@@ -178,8 +178,14 @@ ia32_setup_arg_pages (struct linux_binpr
mpnt->vm_mm = current->mm;
mpnt->vm_start = PAGE_MASK & (unsigned long) bprm->p;
mpnt->vm_end = IA32_STACK_TOP;
- mpnt->vm_page_prot = PAGE_COPY;
- mpnt->vm_flags = VM_STACK_FLAGS;
+ if (executable_stack == EXSTACK_ENABLE_X)
+ mpnt->vm_flags = VM_STACK_FLAGS | VM_EXEC;
+ else if (executable_stack == EXSTACK_DISABLE_X)
+ mpnt->vm_flags = VM_STACK_FLAGS & ~VM_EXEC;
+ else
+ mpnt->vm_flags = VM_STACK_FLAGS;
+ mpnt->vm_page_prot = (mpnt->vm_flags & VM_EXEC)?
+ PAGE_COPY_EXEC: PAGE_COPY;
mpnt->vm_ops = NULL;
mpnt->vm_pgoff = 0;
mpnt->vm_file = NULL;
@@ -192,7 +198,7 @@ ia32_setup_arg_pages (struct linux_binpr
struct page *page = bprm->page[i];
if (page) {
bprm->page[i] = NULL;
- put_dirty_page(current, page, stack_base, PAGE_COPY);
+ put_dirty_page(current, page, stack_base, mpnt->vm_page_prot);
}
stack_base += PAGE_SIZE;
}
diff -uNrp linux-2.6.5-rc2/arch/ia64/ia32/ia32priv.h linux-2.6.5-rc2.nonexecstack/arch/ia64/ia32/ia32priv.h
--- linux-2.6.5-rc2/arch/ia64/ia32/ia32priv.h 2004-03-11 03:55:51.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/ia64/ia32/ia32priv.h 2004-03-24 11:43:04.000000000 +0100
@@ -494,7 +494,7 @@ struct ia32_user_desc {
struct linux_binprm;

extern void ia32_init_addr_space (struct pt_regs *regs);
-extern int ia32_setup_arg_pages (struct linux_binprm *bprm);
+extern int ia32_setup_arg_pages (struct linux_binprm *bprm, int exec_stack);
extern unsigned long ia32_do_mmap (struct file *, unsigned long, unsigned long, int, int, loff_t);
extern void ia32_load_segment_descriptors (struct task_struct *task);

diff -uNrp linux-2.6.5-rc2/arch/mips/kernel/irixelf.c linux-2.6.5-rc2.nonexecstack/arch/mips/kernel/irixelf.c
--- linux-2.6.5-rc2/arch/mips/kernel/irixelf.c 2004-03-11 03:56:03.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/mips/kernel/irixelf.c 2004-03-24 11:43:04.000000000 +0100
@@ -688,7 +688,7 @@ static int load_irix_binary(struct linux
* change some of these later.
*/
current->mm->rss = 0;
- setup_arg_pages(bprm);
+ setup_arg_pages(bprm, EXSTACK_DEFAULT);
current->mm->start_stack = bprm->p;

/* At this point, we assume that the image should be loaded at
diff -uNrp linux-2.6.5-rc2/arch/s390/kernel/binfmt_elf32.c linux-2.6.5-rc2.nonexecstack/arch/s390/kernel/binfmt_elf32.c
--- linux-2.6.5-rc2/arch/s390/kernel/binfmt_elf32.c 2004-03-11 03:55:44.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/s390/kernel/binfmt_elf32.c 2004-03-24 11:43:04.000000000 +0100
@@ -114,7 +114,7 @@ typedef s390_regs32 elf_gregset_t;
#include <linux/binfmts.h>
#include <linux/compat.h>

-int setup_arg_pages32(struct linux_binprm *bprm);
+int setup_arg_pages32(struct linux_binprm *bprm, int executable_stack);

#define elf_prstatus elf_prstatus32
struct elf_prstatus32
@@ -165,7 +165,7 @@ struct elf_prpsinfo32

#undef start_thread
#define start_thread start_thread31
-#define setup_arg_pages(bprm) setup_arg_pages32(bprm)
+#define setup_arg_pages(bprm, exec) setup_arg_pages32(bprm, exec)
#define elf_map elf_map32

MODULE_DESCRIPTION("Binary format loader for compatibility with 32bit Linux for S390 binaries,"
diff -uNrp linux-2.6.5-rc2/arch/s390/kernel/compat_exec.c linux-2.6.5-rc2.nonexecstack/arch/s390/kernel/compat_exec.c
--- linux-2.6.5-rc2/arch/s390/kernel/compat_exec.c 2004-03-11 03:55:44.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/s390/kernel/compat_exec.c 2004-03-24 11:43:04.000000000 +0100
@@ -37,7 +37,7 @@
#undef STACK_TOP
#define STACK_TOP TASK31_SIZE

-int setup_arg_pages32(struct linux_binprm *bprm)
+int setup_arg_pages32(struct linux_binprm *bprm, int executable_stack)
{
unsigned long stack_base;
struct vm_area_struct *mpnt;
@@ -66,6 +66,7 @@ int setup_arg_pages32(struct linux_binpr
mpnt->vm_mm = mm;
mpnt->vm_start = PAGE_MASK & (unsigned long) bprm->p;
mpnt->vm_end = STACK_TOP;
+ /* executable stack setting would be applied here */
mpnt->vm_page_prot = PAGE_COPY;
mpnt->vm_flags = VM_STACK_FLAGS;
mpnt->vm_ops = NULL;
diff -uNrp linux-2.6.5-rc2/arch/sparc64/kernel/binfmt_aout32.c linux-2.6.5-rc2.nonexecstack/arch/sparc64/kernel/binfmt_aout32.c
--- linux-2.6.5-rc2/arch/sparc64/kernel/binfmt_aout32.c 2004-03-11 03:55:27.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/sparc64/kernel/binfmt_aout32.c 2004-03-24 11:43:04.000000000 +0100
@@ -310,7 +310,7 @@ beyond_if:
orig_thr_flags = current_thread_info()->flags;
current_thread_info()->flags |= _TIF_32BIT;

- retval = setup_arg_pages(bprm);
+ retval = setup_arg_pages(bprm, EXSTACK_DEFAULT);
if (retval < 0) {
current_thread_info()->flags = orig_thr_flags;

diff -uNrp linux-2.6.5-rc2/arch/x86_64/ia32/ia32_aout.c linux-2.6.5-rc2.nonexecstack/arch/x86_64/ia32/ia32_aout.c
--- linux-2.6.5-rc2/arch/x86_64/ia32/ia32_aout.c 2004-03-11 03:55:54.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/x86_64/ia32/ia32_aout.c 2004-03-24 11:43:04.000000000 +0100
@@ -35,7 +35,7 @@
#undef WARN_OLD
#undef CORE_DUMP /* probably broken */

-extern int ia32_setup_arg_pages(struct linux_binprm *bprm);
+extern int ia32_setup_arg_pages(struct linux_binprm *bprm, int exec_stack);

static int load_aout_binary(struct linux_binprm *, struct pt_regs * regs);
static int load_aout_library(struct file*);
@@ -395,7 +395,7 @@ beyond_if:

set_brk(current->mm->start_brk, current->mm->brk);

- retval = ia32_setup_arg_pages(bprm);
+ retval = ia32_setup_arg_pages(bprm, EXSTACK_DEFAULT);
if (retval < 0) {
/* Someone check-me: is this error path enough? */
send_sig(SIGKILL, current, 0);
diff -uNrp linux-2.6.5-rc2/arch/x86_64/ia32/ia32_binfmt.c linux-2.6.5-rc2.nonexecstack/arch/x86_64/ia32/ia32_binfmt.c
--- linux-2.6.5-rc2/arch/x86_64/ia32/ia32_binfmt.c 2004-03-24 11:42:03.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/arch/x86_64/ia32/ia32_binfmt.c 2004-03-24 11:44:30.000000000 +0100
@@ -272,8 +272,8 @@ do { \
#define load_elf_binary load_elf32_binary

#define ELF_PLAT_INIT(r, load_addr) elf32_init(r)
-#define setup_arg_pages(bprm) ia32_setup_arg_pages(bprm)
-int ia32_setup_arg_pages(struct linux_binprm *bprm);
+#define setup_arg_pages(bprm, exec_stack) ia32_setup_arg_pages(bprm, exec_stack)
+int ia32_setup_arg_pages(struct linux_binprm *bprm, int executable_stack);

#undef start_thread
#define start_thread(regs,new_rip,new_rsp) do { \
@@ -325,7 +325,7 @@ static void elf32_init(struct pt_regs *r
me->thread.es = __USER_DS;
}

-int setup_arg_pages(struct linux_binprm *bprm)
+int setup_arg_pages(struct linux_binprm *bprm, int executable_stack)
{
unsigned long stack_base;
struct vm_area_struct *mpnt;
@@ -354,7 +354,12 @@ int setup_arg_pages(struct linux_binprm
mpnt->vm_mm = mm;
mpnt->vm_start = PAGE_MASK & (unsigned long) bprm->p;
mpnt->vm_end = IA32_STACK_TOP;
- mpnt->vm_flags = vm_stack_flags32;
+ if (executable_stack == EXSTACK_ENABLE_X)
+ mpnt->vm_flags = vm_stack_flags32 | VM_EXEC;
+ else if (executable_stack == EXSTACK_DISABLE_X)
+ mpnt->vm_flags = vm_stack_flags32 & ~VM_EXEC;
+ else
+ mpnt->vm_flags = vm_stack_flags32;
mpnt->vm_page_prot = (mpnt->vm_flags & VM_EXEC) ?
PAGE_COPY_EXEC : PAGE_COPY;
mpnt->vm_ops = NULL;
@@ -370,7 +375,7 @@ int setup_arg_pages(struct linux_binprm
struct page *page = bprm->page[i];
if (page) {
bprm->page[i] = NULL;
- put_dirty_page(current,page,stack_base,PAGE_COPY_EXEC);
+ put_dirty_page(current,page,stack_base,mpnt->vm_page_prot);
}
stack_base += PAGE_SIZE;
}
diff -uNrp linux-2.6.5-rc2/fs/binfmt_aout.c linux-2.6.5-rc2.nonexecstack/fs/binfmt_aout.c
--- linux-2.6.5-rc2/fs/binfmt_aout.c 2004-03-11 03:55:23.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/fs/binfmt_aout.c 2004-03-24 11:43:04.000000000 +0100
@@ -413,7 +413,7 @@ beyond_if:

set_brk(current->mm->start_brk, current->mm->brk);

- retval = setup_arg_pages(bprm);
+ retval = setup_arg_pages(bprm, EXSTACK_DEFAULT);
if (retval < 0) {
/* Someone check-me: is this error path enough? */
send_sig(SIGKILL, current, 0);
diff -uNrp linux-2.6.5-rc2/fs/binfmt_elf.c linux-2.6.5-rc2.nonexecstack/fs/binfmt_elf.c
--- linux-2.6.5-rc2/fs/binfmt_elf.c 2004-03-24 11:42:03.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/fs/binfmt_elf.c 2004-03-24 11:43:04.000000000 +0100
@@ -476,6 +476,7 @@ static int load_elf_binary(struct linux_
struct exec interp_ex;
char passed_fileno[6];
struct files_struct *files;
+ int executable_stack = EXSTACK_DEFAULT;

/* Get the exec-header */
elf_ex = *((struct elfhdr *) bprm->buf);
@@ -599,6 +600,15 @@ static int load_elf_binary(struct linux_
elf_ppnt++;
}

+ elf_ppnt = elf_phdata;
+ for (i = 0; i < elf_ex.e_phnum; i++, elf_ppnt++)
+ if (elf_ppnt->p_type == PT_GNU_STACK) {
+ if (elf_ppnt->p_flags & PF_X)
+ executable_stack = EXSTACK_ENABLE_X;
+ else
+ executable_stack = EXSTACK_DISABLE_X;
+ }
+
/* Some simple consistency checks for the interpreter */
if (elf_interpreter) {
interpreter_type = INTERPRETER_ELF | INTERPRETER_AOUT;
@@ -674,7 +684,7 @@ static int load_elf_binary(struct linux_
change some of these later */
current->mm->rss = 0;
current->mm->free_area_cache = TASK_UNMAPPED_BASE;
- retval = setup_arg_pages(bprm);
+ retval = setup_arg_pages(bprm, executable_stack);
if (retval < 0) {
send_sig(SIGKILL, current, 0);
goto out_free_dentry;
diff -uNrp linux-2.6.5-rc2/fs/binfmt_som.c linux-2.6.5-rc2.nonexecstack/fs/binfmt_som.c
--- linux-2.6.5-rc2/fs/binfmt_som.c 2004-03-11 03:55:25.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/fs/binfmt_som.c 2004-03-24 11:43:04.000000000 +0100
@@ -254,7 +254,7 @@ load_som_binary(struct linux_binprm * bp

set_binfmt(&som_format);
compute_creds(bprm);
- setup_arg_pages(bprm);
+ setup_arg_pages(bprm, EXSTACK_DEFAULT);

create_som_tables(bprm);

diff -uNrp linux-2.6.5-rc2/fs/exec.c linux-2.6.5-rc2.nonexecstack/fs/exec.c
--- linux-2.6.5-rc2/fs/exec.c 2004-03-11 03:55:25.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/fs/exec.c 2004-03-24 11:43:04.000000000 +0100
@@ -342,7 +342,7 @@ out_sig:
return;
}

-int setup_arg_pages(struct linux_binprm *bprm)
+int setup_arg_pages(struct linux_binprm *bprm, int executable_stack)
{
unsigned long stack_base;
struct vm_area_struct *mpnt;
@@ -425,8 +425,16 @@ int setup_arg_pages(struct linux_binprm
mpnt->vm_start = PAGE_MASK & (unsigned long) bprm->p;
mpnt->vm_end = STACK_TOP;
#endif
- mpnt->vm_page_prot = protection_map[VM_STACK_FLAGS & 0x7];
- mpnt->vm_flags = VM_STACK_FLAGS;
+ /* Adjust stack execute permissions; explicitly enable
+ * for EXSTACK_ENABLE_X, disable for EXSTACK_DISABLE_X
+ * and leave alone (arch default) otherwise. */
+ if (unlikely(executable_stack == EXSTACK_ENABLE_X))
+ mpnt->vm_flags = VM_STACK_FLAGS | VM_EXEC;
+ else if (executable_stack == EXSTACK_DISABLE_X)
+ mpnt->vm_flags = VM_STACK_FLAGS & ~VM_EXEC;
+ else
+ mpnt->vm_flags = VM_STACK_FLAGS;
+ mpnt->vm_page_prot = protection_map[mpnt->vm_flags & 0x7];
mpnt->vm_ops = NULL;
mpnt->vm_pgoff = 0;
mpnt->vm_file = NULL;
diff -uNrp linux-2.6.5-rc2/include/linux/binfmts.h linux-2.6.5-rc2.nonexecstack/include/linux/binfmts.h
--- linux-2.6.5-rc2/include/linux/binfmts.h 2004-03-11 03:55:27.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/include/linux/binfmts.h 2004-03-24 11:43:10.000000000 +0100
@@ -58,7 +58,13 @@ extern int prepare_binprm(struct linux_b
extern void remove_arg_zero(struct linux_binprm *);
extern int search_binary_handler(struct linux_binprm *,struct pt_regs *);
extern int flush_old_exec(struct linux_binprm * bprm);
-extern int setup_arg_pages(struct linux_binprm * bprm);
+
+/* Stack area protections */
+#define EXSTACK_DEFAULT 0 /* Whatever the arch defaults to */
+#define EXSTACK_DISABLE_X 1 /* Disable executable stacks */
+#define EXSTACK_ENABLE_X 2 /* Enable executable stacks */
+
+extern int setup_arg_pages(struct linux_binprm * bprm, int executable_stack);
extern int copy_strings(int argc,char __user * __user * argv,struct linux_binprm *bprm);
extern int copy_strings_kernel(int argc,char ** argv,struct linux_binprm *bprm);
extern void compute_creds(struct linux_binprm *binprm);
diff -uNrp linux-2.6.5-rc2/include/linux/elf.h linux-2.6.5-rc2.nonexecstack/include/linux/elf.h
--- linux-2.6.5-rc2/include/linux/elf.h 2004-03-11 03:55:23.000000000 +0100
+++ linux-2.6.5-rc2.nonexecstack/include/linux/elf.h 2004-03-24 11:43:04.000000000 +0100
@@ -35,6 +35,8 @@ typedef __s64 Elf64_Sxword;
#define PT_HIPROC 0x7fffffff
#define PT_GNU_EH_FRAME 0x6474e550

+#define PT_GNU_STACK (PT_LOOS + 0x474e551)
+
/* These constants define the different elf file types */
#define ET_NONE 0
#define ET_REL 1

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