by Jake Moilanen

[permalink] [raw]

Subject: Re: [PATCH 1/2] No-exec support for ppc64

On Wed, 16 Mar 2005 17:10:57 +1100
Paul Mackerras <[email protected]> wrote:

> Jake Moilanen writes:
>
> > It does not work w/o the sys_mprotect. It will hang in one of the first
> > few binaries.
>
> Hmmm, what distro is this with? I just tried a kernel with the patch
> below on a SLES9 install and a Debian install and it came up and ran
> just fine in both cases.

I'm not sure that the patch you sent is actually doing protection
correctly.

To test I commented out this line:

> +#define elf_read_implies_exec(ex, have_pt_gnu_stack) (!(have_pt_gnu_stack))

and then ran a non-pt_gnu_stack binary which should have executed on a non-exec
segment, it did not segfault.

> + *
> + * Note due to the way vm flags are laid out, the bits are XWR
> */
> #define __P000 PAGE_NONE
> -#define __P001 PAGE_READONLY_X
> +#define __P001 PAGE_READONLY
> #define __P010 PAGE_COPY
> #define __P011 PAGE_COPY_X
> #define __P100 PAGE_READONLY
> #define __P101 PAGE_READONLY_X
> -#define __P110 PAGE_COPY
> +#define __P110 PAGE_COPY_X
> #define __P111 PAGE_COPY_X

I think the problem was this hunk. __P011 should be PAGE_COPY and
__P100 should be PAGE_READONLY_X.

Here is a patch ontop of the last patch you sent to fix this problem and
take another crack at doing the sys_mprotect less hackish.

Signed-off-by: Jake Moilanen <[email protected]>

---

linux-2.6.11.4-paulus-moilanen/fs/binfmt_elf.c | 18 +++++++++----
linux-2.6.11.4-paulus-moilanen/include/asm-ppc64/pgtable.h | 4 +-
2 files changed, 15 insertions(+), 7 deletions(-)

diff -puN fs/binfmt_elf.c~more-nx fs/binfmt_elf.c
--- linux-2.6.11.4-paulus/fs/binfmt_elf.c~more-nx 2005-03-16 09:35:28 -06:00
+++ linux-2.6.11.4-paulus-moilanen/fs/binfmt_elf.c 2005-03-16 11:03:15 -06:00
@@ -88,7 +88,7 @@ static struct linux_binfmt elf_format =

#define BAD_ADDR(x) ((unsigned long)(x) > TASK_SIZE)

-static int set_brk(unsigned long start, unsigned long end)
+static int set_brk(unsigned long start, unsigned long end, int prot)
{
start = ELF_PAGEALIGN(start);
end = ELF_PAGEALIGN(end);
@@ -99,6 +99,9 @@ static int set_brk(unsigned long start,
up_write(&current->mm->mmap_sem);
if (BAD_ADDR(addr))
return addr;
+
+ sys_mprotect(start, end-start, prot);
+
}
current->mm->start_brk = current->mm->brk = end;
return 0;
@@ -529,6 +532,7 @@ static int load_elf_binary(struct linux_
struct files_struct *files;
int have_pt_gnu_stack, executable_stack = EXSTACK_DEFAULT;
unsigned long def_flags = 0;
+ int bss_prot = 0;
struct {
struct elfhdr elf_ex;
struct elfhdr interp_elf_ex;
@@ -811,7 +815,7 @@ static int load_elf_binary(struct linux_
before this one. Map anonymous pages, if needed,
and clear the area. */
retval = set_brk (elf_bss + load_bias,
- elf_brk + load_bias);
+ elf_brk + load_bias, bss_prot);
if (retval) {
send_sig(SIGKILL, current, 0);
goto out_free_dentry;
@@ -883,15 +887,19 @@ static int load_elf_binary(struct linux_

k = elf_ppnt->p_vaddr + elf_ppnt->p_filesz;

- if (k > elf_bss)
+ if (k > elf_bss) {
elf_bss = k;
+ bss_prot = elf_prot;
+ }
if ((elf_ppnt->p_flags & PF_X) && end_code < k)
end_code = k;
if (end_data < k)
end_data = k;
k = elf_ppnt->p_vaddr + elf_ppnt->p_memsz;
- if (k > elf_brk)
+ if (k > elf_brk) {
elf_brk = k;
+ bss_prot = elf_prot;
+ }
}

loc->elf_ex.e_entry += load_bias;
@@ -907,7 +915,7 @@ static int load_elf_binary(struct linux_
* mapping in the interpreter, to make sure it doesn't wind
* up getting placed where the bss needs to go.
*/
- retval = set_brk(elf_bss, elf_brk);
+ retval = set_brk(elf_bss, elf_brk, bss_prot);
if (retval) {
send_sig(SIGKILL, current, 0);
goto out_free_dentry;
diff -puN include/asm-ppc64/pgtable.h~more-nx include/asm-ppc64/pgtable.h
--- linux-2.6.11.4-paulus/include/asm-ppc64/pgtable.h~more-nx 2005-03-16 09:35:44 -06:00
+++ linux-2.6.11.4-paulus-moilanen/include/asm-ppc64/pgtable.h 2005-03-16 09:35:53 -06:00
@@ -137,8 +137,8 @@
#define __P000 PAGE_NONE
#define __P001 PAGE_READONLY
#define __P010 PAGE_COPY
-#define __P011 PAGE_COPY_X
-#define __P100 PAGE_READONLY
+#define __P011 PAGE_COPY
+#define __P100 PAGE_READONLY_X
#define __P101 PAGE_READONLY_X
#define __P110 PAGE_COPY_X
#define __P111 PAGE_COPY_X

_