LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
* [PATCH] elf: fix "start_code" evaluation
@ 2019-05-23 17:57 Alexey Dobriyan
  2019-05-23 18:44 ` Andrew Morton
  0 siblings, 1 reply; 3+ messages in thread
From: Alexey Dobriyan @ 2019-05-23 17:57 UTC (permalink / raw)
  To: akpm; +Cc: linux-kernel

Only executable ELF program headers should change ->start_code.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/binfmt_elf.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -1026,7 +1026,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
 			}
 		}
 		k = elf_ppnt->p_vaddr;
-		if (k < start_code)
+		if ((elf_ppnt->p_flags & PF_X) && k < start_code)
 			start_code = k;
 		if (start_data < k)
 			start_data = k;

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] elf: fix "start_code" evaluation
  2019-05-23 17:57 [PATCH] elf: fix "start_code" evaluation Alexey Dobriyan
@ 2019-05-23 18:44 ` Andrew Morton
  2019-05-23 19:35   ` Alexey Dobriyan
  0 siblings, 1 reply; 3+ messages in thread
From: Andrew Morton @ 2019-05-23 18:44 UTC (permalink / raw)
  To: Alexey Dobriyan; +Cc: linux-kernel

On Thu, 23 May 2019 20:57:36 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:

> Only executable ELF program headers should change ->start_code.
> 
> ...
>
> --- a/fs/binfmt_elf.c
> +++ b/fs/binfmt_elf.c
> @@ -1026,7 +1026,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
>  			}
>  		}
>  		k = elf_ppnt->p_vaddr;
> -		if (k < start_code)
> +		if ((elf_ppnt->p_flags & PF_X) && k < start_code)
>  			start_code = k;
>  		if (start_data < k)
>  			start_data = k;

What problem does this solve?  How does it alter runtime behaviour? 
How do we know it won't break anything?


^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] elf: fix "start_code" evaluation
  2019-05-23 18:44 ` Andrew Morton
@ 2019-05-23 19:35   ` Alexey Dobriyan
  0 siblings, 0 replies; 3+ messages in thread
From: Alexey Dobriyan @ 2019-05-23 19:35 UTC (permalink / raw)
  To: Andrew Morton; +Cc: linux-kernel

On Thu, May 23, 2019 at 11:44:17AM -0700, Andrew Morton wrote:
> On Thu, 23 May 2019 20:57:36 +0300 Alexey Dobriyan <adobriyan@gmail.com> wrote:
> 
> > Only executable ELF program headers should change ->start_code.
> > 
> > ...
> >
> > --- a/fs/binfmt_elf.c
> > +++ b/fs/binfmt_elf.c
> > @@ -1026,7 +1026,7 @@ static int load_elf_binary(struct linux_binprm *bprm)
> >  			}
> >  		}
> >  		k = elf_ppnt->p_vaddr;
> > -		if (k < start_code)
> > +		if ((elf_ppnt->p_flags & PF_X) && k < start_code)
> >  			start_code = k;
> >  		if (start_data < k)
> >  			start_data = k;
> 
> What problem does this solve?

It is a bug. Look at the ->end_code update:

	if ((elf_ppnt->p_flags & PF_X) && end_code < k)
		end_code = k;

> How does it alter runtime behaviour?

It makes "VmExe" and "VmLib" accounting more accurate for common case.

> How do we know it won't break anything?

We don't. Some distros are unaffected because they ship binaries with
first PT_LOAD segment being executable (Debian 8). Some don't.

Regardless, these fields are lies: ELF binary can have multiple disjoint
PT_LOAD segments, but all those ->start and ->end fields assume everything
is mapped together.

Hopefully nobody actually uses them for anything serious.

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, other threads:[~2019-05-23 19:35 UTC | newest]

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-05-23 17:57 [PATCH] elf: fix "start_code" evaluation Alexey Dobriyan
2019-05-23 18:44 ` Andrew Morton
2019-05-23 19:35   ` Alexey Dobriyan

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).