Re: [Bug 11063] New: lack of GNU_STACK header doesn't result in rwxstack on i386

[Andrew Morton]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Wed,  9 Jul 2008 12:13:05 -0700 (PDT) bugme-daemon@xxxxxxxxxxxxxxxxxxx wrote:

> http://bugzilla.kernel.org/show_bug.cgi?id=11063
> 
>            Summary: lack of GNU_STACK header doesn't result in rwx stack on
>                     i386
>            Product: Memory Management
>            Version: 2.5
>           Platform: All
>         OS/Version: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: Other
>         AssignedTo: akpm@xxxxxxxx
>         ReportedBy: pageexec@xxxxxxxxxxx
> 
> 
> Latest working kernel version: unknown, probably before the introduction of
> unlimited argv
> Earliest failing kernel version: unknown, probably after the introduction of
> unlimited argv, 2.6.26-rc9 definitely fails
> Distribution:
> Hardware Environment:
> Software Environment:
> Problem Description:
> ELF/i386 traditionally has an executable stack which in the PT_GNU_STACK world
> is provided two ways: if the ELF has a RWE PT_GNU_STACK program header or if it
> lacks that program header. due to this regression, the latter case results in a
> non-executable stack with corresponding breakage of (old) userland binaries
> that use nested function trampolines.
> 
> this bug was probably introduced when the unlimited argv feature was merged: in
> that system the stack vma (and its vm_flags) is initialized too early, before
> the incoming process' ELF header is consulted, which on i386 means that the
> personality used for determining the executable status of the stack is that of
> the old process, not the incoming one. later, in setup_arg_pages, only the
> explicit setting (disable/enable) of stack executability is honoured,
> EXSTACK_DEFAULT isn't consulted (i guess the assumption was that the initial
> ->vm_flags setting got it right).
> 
> Steps to reproduce: run any ELF that lacks a PT_GNU_STACK program header and
> check its stack vma, it'll be rw-, instead of rwx.
> 

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