Useless stack randomization patch

Useless stack randomization patch

[Franck Bui-Huu]

Ralf,

We started stack inside page randomization through commit
941091024ef0f2f7e09eb81201d293ac18833cc8 but it currently does nothing
usefull because ELF_PLATFORM is not defined on MIPS (see
fs/binfm_elf.c, create_elf_tables() for details).

I tried several times to get information on lkml about that dependency
but unfortunately I got no answer.

I'm not sure how ELF_PLATFORM is used by ld.so and I don't think it's
a good idea to define it just for enabling stack randomization.

What do you think ?

thanks
		Franck

Re: Useless stack randomization patch

[Markus Gothe]

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Franck Bui-Huu wrote:
> Ralf,
>
> We started stack inside page randomization through commit
> 941091024ef0f2f7e09eb81201d293ac18833cc8 but it currently does nothing
> usefull because ELF_PLATFORM is not defined on MIPS (see
> fs/binfm_elf.c, create_elf_tables() for details).
>
> I tried several times to get information on lkml about that dependency
> but unfortunately I got no answer.
>
> I'm not sure how ELF_PLATFORM is used by ld.so and I don't think it's
> a good idea to define it just for enabling stack randomization.
>
> What do you think ?
>
> thanks
>         Franck
>
I think you mean this in specific:

"/* This yields a string that ld.so will use to load implementation
   specific libraries for optimization.  This is more specific in
   intent than poking at uname or /proc/cpuinfo.

   For the moment, we have only optimizations for the Intel generations,
   but that could change... */

#define ELF_PLATFORM  (NULL)"

Right?

- --
_______________________________________

Mr Markus Gothe
Software Engineer

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Re: Useless stack randomization patch

[Franck Bui-Huu]

Markus Gothe wrote:
> I think you mean this in specific:
> 
> "/* This yields a string that ld.so will use to load implementation
>    specific libraries for optimization.  This is more specific in
>    intent than poking at uname or /proc/cpuinfo.
> 
>    For the moment, we have only optimizations for the Intel generations,
>    but that could change... */
> 
> #define ELF_PLATFORM  (NULL)"
> 
> Right?
> 

Correct...

		Franck

Re: Useless stack randomization patch

[Ralf Baechle]

On Wed, Sep 26, 2007 at 04:10:14PM +0200, Franck Bui-Huu wrote:

> We started stack inside page randomization through commit
> 941091024ef0f2f7e09eb81201d293ac18833cc8 but it currently does nothing
> usefull because ELF_PLATFORM is not defined on MIPS (see
> fs/binfm_elf.c, create_elf_tables() for details).
> 
> I tried several times to get information on lkml about that dependency
> but unfortunately I got no answer.

lkml has turned into a posting-only mailing list.  I've stopped reading
it years ago; the volume is so insane that I only use it to occasionally
to follow references from other sources.  So don't be surprised if you
don't get an answer.  Linus does not read lkml either.

> I'm not sure how ELF_PLATFORM is used by ld.so and I don't think it's
> a good idea to define it just for enabling stack randomization.
> 
> What do you think ?

I suppose we should give it a sane definition.  Not sure what would be
useful, if it should be like an ASCII string with the processor type or
more corse grained like just "mips32r2", should ASEs be mentioned ...

  Ralf

Re: Useless stack randomization patch

[Franck Bui-Huu]

Ralf Baechle wrote:
> On Wed, Sep 26, 2007 at 04:10:14PM +0200, Franck Bui-Huu wrote:
> I suppose we should give it a sane definition.  Not sure what would be
> useful, if it should be like an ASCII string with the processor type or
> more corse grained like just "mips32r2", should ASEs be mentioned ...
> 

Well before giving any sane definition, shouldn't we know why this
dependency (ELF_PLATFORM/sp-randomization) exists at all...

Is something like the patch below better ?

		Franck

-- 8< --


diff --git a/fs/binfmt_elf.c b/fs/binfmt_elf.c
index 43143c5..e8713fb 100644
--- a/fs/binfmt_elf.c
+++ b/fs/binfmt_elf.c
@@ -150,6 +150,13 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	struct vm_area_struct *vma;
 
 	/*
+	 * In some cases (e.g. Hyper-Threading), we want to avoid L1
+	 * evictions by the processes running on the same package. One
+	 * thing we can do is to shuffle the initial stack for them.
+	 */
+	p = arch_align_stack(p);
+
+	/*
 	 * If this architecture has a platform capability string, copy it
 	 * to userspace.  In some cases (Sparc), this info is impossible
 	 * for userspace to get any other way, in others (i386) it is
@@ -159,14 +166,6 @@ create_elf_tables(struct linux_binprm *bprm, struct elfhdr *exec,
 	if (k_platform) {
 		size_t len = strlen(k_platform) + 1;
 
-		/*
-		 * In some cases (e.g. Hyper-Threading), we want to avoid L1
-		 * evictions by the processes running on the same package. One
-		 * thing we can do is to shuffle the initial stack for them.
-		 */
-
-		p = arch_align_stack(p);
-
 		u_platform = (elf_addr_t __user *)STACK_ALLOC(p, len);
 		if (__copy_to_user(u_platform, k_platform, len))
 			return -EFAULT;

Re: Useless stack randomization patch

[Ralf Baechle]

On Wed, Sep 26, 2007 at 05:20:10PM +0200, Franck Bui-Huu wrote:

> Ralf Baechle wrote:
> > On Wed, Sep 26, 2007 at 04:10:14PM +0200, Franck Bui-Huu wrote:
> > I suppose we should give it a sane definition.  Not sure what would be
> > useful, if it should be like an ASCII string with the processor type or
> > more corse grained like just "mips32r2", should ASEs be mentioned ...
> > 
> 
> Well before giving any sane definition, shouldn't we know why this
> dependency (ELF_PLATFORM/sp-randomization) exists at all...
> 
> Is something like the patch below better ?

Yes, I think that makes more sense.

  Ralf