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

["Arnd Bergmann" <arnd@arndb.de>]

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.

There are two related bits I don't quite understand:

- Do we still care about EF_ALPHA_32BIT? I see that it gets set by
 "alpha-linux-ld.bfd --taso", but could not find any documentation
 on what that flag is actually good for. On all other architectures,
 the address space limit gets enforced through a per-thread setting
 like TIF_32BIT, not through the personality that gets inherited
 by the child processes.

- all architectures other than x86 mask out the lower byte. Why
  not that one?

       Arnd