Messages in this thread | | | From | Sami Tolvanen <> | Date | Tue, 22 Oct 2019 12:26:02 -0700 | Subject | Re: [PATCH 06/18] add support for Clang's Shadow Call Stack (SCS) |
| |
On Tue, Oct 22, 2019 at 9:28 AM Mark Rutland <mark.rutland@arm.com> wrote: > I think it would be preferable to follow the example of CC_FLAGS_FTRACE > so that this can be filtered out, e.g. > > ifdef CONFIG_SHADOW_CALL_STACK > CFLAGS_SCS := -fsanitize=shadow-call-stack > KBUILD_CFLAGS += $(CFLAGS_SCS) > export CC_FLAGS_SCS > endif
Sure, SGTM.
> > +choice > > + prompt "Return-oriented programming (ROP) protection" > > + default ROP_PROTECTION_NONE > > + help > > + This option controls kernel protections against return-oriented > > + programming (ROP) attacks. > > Are we expecting more options here in future?
Yes, I believe we'd be interested in seeing PAC support too once hardware is more readily available.
> I think it would be better to ./make that depend on !SHADOW_CALL_STACK, as > it's plausible that we can add a different ROP protection mechanism that > is compatible with kretprobes.
OK, I can change that and remove the choice. We can always add it back when other alternatives are added.
> > +config SHADOW_CALL_STACK > > + bool "Clang Shadow Call Stack" > > + depends on ARCH_SUPPORTS_SHADOW_CALL_STACK > > + depends on CC_IS_CLANG && CLANG_VERSION >= 70000 > > Is there a reason for an explicit version check rather than a > CC_HAS_<feature> check? e.g. was this available but broken in prior > versions of clang?
No, this feature was added in Clang 7. However, -fsanitize=shadow-call-stack might require architecture-specific flags, so a simple $(cc-option, -fsanitize=shadow-call-stack) in arch/Kconfig is not going to work. I could add something like this to arch/arm64/Kconfig though:
select ARCH_SUPPORTS_SHADOW_CALL_STACK if CC_HAVE_SHADOW_CALL_STACK ... config CC_HAVE_SHADOW_CALL_STACK def_bool $(cc-option, -fsanitize=shadow-call-stack -ffixed-x18)
And then drop CC_IS_CLANG and version check entirely. Thoughts?
> > +#define SCS_GFP (GFP_KERNEL | __GFP_ZERO) > > Normally GFP_ is a prefix. For consistency, GFP_SCS would be preferable.
Ack.
> > +extern unsigned long init_shadow_call_stack[]; > > Do we need this exposed here? IIUC this is only assigned by assembly in > arch code.
True, it's not needed.
> [...] > > > +void scs_set_init_magic(struct task_struct *tsk) > > +{ > > + scs_save(tsk); > > + scs_set_magic(tsk); > > + scs_load(tsk); > > +} > > Can we initialize this at compile time instead?
We can. I'll change this and drop the function.
Sami
| |