Hi Miodrag,
> When kernel is detecting the type of mapping it should apply :
>
> fs/binfmt_elf.c:
> ...
> if (elf_read_implies_exec(loc->elf_ex, executable_stack))
> current->personality |= READ_IMPLIES_EXEC;
> ...
>
> this effectively calls mips_elf_read_implies_exec() which performs a check:
> ...
> if (!cpu_has_rixi) {
> /* The CPU doesn't support non-executable memory */
> return 1;
> }
>
> return 0;
> }
>
> This will in turn make stack & heap executable on processors without
> RIXI, which are practically all processors with MIPS ISA R < 6.
>
> We would like to have an option to override this and force
> non-executable mappings for such systems.
Of course you can't force a non-executable mapping with a system where
all valid pages are executable, as David has already noted. Did you mean
the other condition, that is:
if (exstack != EXSTACK_DISABLE_X) {
/* The binary doesn't request a non-executable stack */
return 1;
}
? In which case you do want to respect the lack of the RIXI feature,
i.e.:
int mips_elf_read_implies_exec(void *elf_ex, int exstack)
{
if (!cpu_has_rixi) {
/* The CPU doesn't support non-executable memory */
return 1;
}
switch (nonxstack) {
case EXSTACK_DISABLE_X:
return 0;
case EXSTACK_ENABLE_X:
return 1;
default:
break;
}
if (exstack != EXSTACK_DISABLE_X) {
/* The binary doesn't request a non-executable stack */
return 1;
}
return 0;
}
(I'd replace `break' with `return exstack != EXSTACK_DISABLE_X' and
discard the code that follows, but that can be a separate optimisation).
What problem are you trying to solve anyway? Is it not something that
can be handled with the `execstack' utility?
NB as someone has observed with programs that do not request a
non-executable stack we actually propagate the execute permission to all
data pages. Is it not something we would want to handle differently?
Maciej
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