Re: [PATCH] alpha: Fix personality flag propagation across an exec

[John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>]

Hi Arnd,

thanks a lot for your feedback!

On Thu, 2025-01-09 at 09:43 +0100, Arnd Bergmann wrote:
> On Thu, Jan 9, 2025, at 09:01, Arnd Bergmann wrote:
> > On Fri, Jan 3, 2025, at 15:01, John Paul Adrian Glaubitz wrote:
> > 
> > > 
> > >  #define SET_PERSONALITY(EX)					\
> > > -	set_personality(((EX).e_flags & EF_ALPHA_32BIT)		\
> > > -	   ? PER_LINUX_32BIT : PER_LINUX)
> > > +	set_personality((((EX).e_flags & EF_ALPHA_32BIT)	\
> > > +	   ? PER_LINUX_32BIT : PER_LINUX) | (current->personality & (~PER_MASK)))
> > 
> > This looks wrong to me: since ADDR_LIMIT_32BIT is not part of
> > PER_MASK, executing a regular binary from a taso binary no longer
> > reverts back to the entire 64-bit address space.
> > 
> > It seems that the behavior on most other architectures changed in 2012
> > commit 16f3e95b3209 ("cross-arch: don't corrupt personality flags upon
> > exec()").
> > 
> > At the time, the same bug existed on mips, parisc and tile, but those
> > got fixed quickly.
> 
> Correction: from what I can tell, mips still has the bug (and now
> also loongarch), it's just in SET_PERSONALITY2() now instead of
> SET_PERSONALITY():
> 
>         current->personality &= ~READ_IMPLIES_EXEC;
>         ...
>         p = personality(current->personality);                          \
>         if (p != PER_LINUX32 && p != PER_LINUX)                         \
>                 set_personality(PER_LINUX);                             \
> 
> personality() only returns the lower 8 bits (execution domain),
> so if any of them are set (BSD/HPUX/IRIX32/IRIX64/...), both
> the upper and the lower bits are cleared, otherwise neither
> of them are.
> 
> The behavior on the other architectures is that we clear the
> lower bits but keep the upper ones.

So, if I understand this correctly, we should just use PER_MASK on alpha
for 64-bit executables and allow the bits to be cleared for 32-bit binaries?

Adrian

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