Date: Wed, 21 Jun 2017 10:24:56 +0100 From: Mark Rutland <mark.rutland@....com> To: Kees Cook <keescook@...omium.org> Cc: Laura Abbott <labbott@...hat.com>, Alexander Popov <alex.popov@...ux.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, PaX Team <pageexec@...email.hu>, Brad Spengler <spender@...ecurity.net>, Tycho Andersen <tycho@...ker.com>, Ard Biesheuvel <ard.biesheuvel@...aro.org> Subject: Re: Re: [PATCH RFC v2 1/1] gcc-plugins: Add stackleak feature erasing the kernel stack at the end of syscalls On Tue, Jun 20, 2017 at 12:11:56PM -0700, Kees Cook wrote: > On Tue, Jun 20, 2017 at 4:20 AM, Mark Rutland <mark.rutland@....com> wrote: > > On Tue, Jun 13, 2017 at 02:51:59PM -0700, Laura Abbott wrote: > >> On 06/09/2017 10:28 AM, Kees Cook wrote: > >> > It seems like it shouldn't be too hard to add on-user-return erasure > >> > code to other architectures too. > >> > >> I played around getting this to compile for arm64 with a dummy > >> stack clearing function. arm64 is doing something special with the > >> efistub so it fails to link with > >> > >> drivers/firmware/efi/libstub/arm-stub.c:45:(.init.text+0x54): relocation > >> truncated to fit: R_AARCH64_CALL26 against undefined symbol `__efistub_track_stack' > >> > >> The relocation to the .init.text section and appending __efistub happens after > >> compilation so the checks in the plugin itself don't work. I haven't come up > >> with a solution to not have the plugin run on the stub yet. > > > > Can we do something like what we do for KCOV, and (only) place the > > plugin-invoking flags to into CFLAGS_STACKLEAK, which we can filter out > > in scripts/Makefile.lib? > > That seems fine to me, though plugins have tended to provide a > DISABLE_foo_bar_PLUGIN export (like used in ppc for turning off the > latent entropy plugin): > > scripts/Makefile.gcc-plugins: DISABLE_LATENT_ENTROPY_PLUGIN += > -fplugin-arg-latent_entropy_plugin-disable > > arch/powerpc/kernel/Makefile:CFLAGS_cputable.o += > $(DISABLE_LATENT_ENTROPY_PLUGIN) > arch/powerpc/kernel/Makefile:CFLAGS_prom_init.o += > $(DISABLE_LATENT_ENTROPY_PLUGIN) > ... Interesting. I hadn't encountered that style before. I'd seen the per-makefile config disables: drivers/firmware/efi/libstub/Makefile:GCOV_PROFILE := n drivers/firmware/efi/libstub/Makefile:KASAN_SANITIZE := n drivers/firmware/efi/libstub/Makefile:UBSAN_SANITIZE := n drivers/firmware/efi/libstub/Makefile:KCOV_INSTRUMENT := n ... and per-object config disables: arch/arm64/mm/Makefile:KASAN_SANITIZE_physaddr.o += n arch/arm64/mm/Makefile:KASAN_SANITIZE_kasan_init.o := n ... which AFAICT are both handled by the standard scripts/Makefile.lib idiom: ifeq ($(CONFIG_KASAN),y) _c_flags += $(if $(patsubst n%,, \ $(KASAN_SANITIZE_$(basetarget).o)$(KASAN_SANITIZE)y), \ $(CFLAGS_KASAN)) endif ... it seems a shame for plugins to follow a different pattern. Thanks, Mark.
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