Re: [PATCH v4 1/2] module: add elf_check_module_arch for module specific elf arch checks

Segher Boessenkool [off-list ref] writes:

On Tue, Jun 15, 2021 at 03:41:00PM +0200, Jessica Yu wrote:

quoted

+++ Segher Boessenkool [15/06/21 07:50 -0500]:

quoted

On Tue, Jun 15, 2021 at 02:17:40PM +0200, Jessica Yu wrote:

quoted

+int __weak elf_check_module_arch(Elf_Ehdr *hdr)
+{
+       return 1;
+}

But is this a good idea?  It isn't useful to be able to attempt to load
a module not compiled for your architecture, and it increases the attack
surface tremendously.  These checks are one of the few things that can
*not* be weak symbols, imo.

Hm, could you please elaborate a bit more? This patchset is adding
extra Elf header checks specifically for powerpc, and the module
loader usually provides arch-specific hooks via weak symbols. We are
just providing an new hook here, which should act as a no-op if it
isn't used.

So if an architecture wants to provide extra header checks, it can do
so by overriding the new weak symbol. Otherwise, the weak function acts as
a noop. We also already have the existing elf_check_arch() check for each
arch and that is *not* a weak symbol.

The way I read your patch the default elf_check_module_arch does not
call elf_check_arch?  Is that clearly called elsewhere and I'm just
dumb again?  Sorry for the distraction in that case :-/

Yeah elf_check_arch() is already called from elf_validity_check(), and
that call would remain.

cheers