Re: [PATCH] MIPS: Prevent READ_IMPLIES_EXEC propagation

[Tiezhu Yang]

On 07/08/2020 03:45 AM, Maciej W. Rozycki wrote:
> On Tue, 7 Jul 2020, Tiezhu Yang wrote:
>
> > In the MIPS architecture, we should clear the security-relevant
> > flag READ_IMPLIES_EXEC in the function SET_PERSONALITY2() of the
> > file arch/mips/include/asm/elf.h.
> >
> > Otherwise, with this flag set, PROT_READ implies PROT_EXEC for
> > mmap to make memory executable that is not safe, because this
> > condition allows an attacker to simply jump to and execute bytes
> > that are considered to be just data [1].
>   Why isn't the arrangement made with `mips_elf_read_implies_exec'
> sufficient?

We inherit the READ_IMPLIES_EXEC personality flag across fork().
If we do not explicitly clear this flag in SET_PERSONALITY2(),
PROT_READ implies PROT_EXEC for mmap to make memory executable
even if used with the GCC option "-z noexecstack" when compile.

By the way, we can see some other reasons in the following commit:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=48f99c8ec0b2

>    Maciej