issues w/init

[Kumar Gala]

On Apr 17, 2009, at 5:41 AM, Benjamin Herrenschmidt wrote:

> On Fri, 2009-04-17 at 20:05 +1000, Paul Mackerras wrote:
>> Benjamin Herrenschmidt writes:
>>
>>> I'm pretty sure they are broken already when running off a 64-bit
>>> kernel,
>>
>> Maybe not... for 64-bit kernels we have our definition of
>> elf_read_implies_exec in arch/powerpc/include/asm/elf.h, which IIRC
>> sets the read-implies-exec personality thing on old 32-bit binaries.
>
> Ok, so looking at that more closely, if that had worked, we would
> have had PROT_EXEC, and thus VM_EXEC added to the vma by mmap... which
> apparently didn't occur.
>
> I think what may be happening is that the binary he's running has the
> PT_GNU_STACK but his libc doesn't ... the kernel will set the
> personality flag based on the binary you are trying to run, not any
> library it uses...
>
> Kumar, can you try to instrument that a bit and tell us ? What the
> personality flag gets set to and whether mmap sets PROT_EXEC ?

On ppc32 personality is clearly set to 0.  On ppc64 the  
elf_read_implies_exec does work around the issue (ie I implemented  
elf_read_implies_exec as (exec_stk != EXSTACK_DISABLE_X) on ppc32).   
However I think its just masking it.

Hear are the PHDRs for the version of init I'm running:

Program Headers:
   Type           Offset   VirtAddr   PhysAddr   FileSiz MemSiz  Flg  
Align
   PHDR           0x000034 0x10000034 0x10000034 0x000e0 0x000e0 R E 0x4
   INTERP         0x000114 0x10000114 0x10000114 0x0000d 0x0000d R   0x1
       [Requesting program interpreter: /lib/ld.so.1]
   LOAD           0x000000 0x10000000 0x10000000 0x072a0 0x072a0 R E  
0x10000
   LOAD           0x0072a0 0x100172a0 0x100172a0 0x00358 0x00988 RW   
0x10000
   DYNAMIC        0x0074bc 0x100174bc 0x100174bc 0x000c8 0x000c8 RW  0x4
   NOTE           0x000130 0x10000130 0x10000130 0x00020 0x00020 R    
0x10

I don't think elf_read_implies_exec() is the right solution on ppc32.   
As I asked before, can VM_MAYEXEC be of any use to us?

- k