On Fri, Oct 18, 2019 at 09:10:21AM -0700, Sami Tolvanen wrote: > This change adds generic support for Clang's Shadow Call Stack, which > uses a shadow stack to protect return addresses from being overwritten > by an attacker. Details are available here: > > https://clang.llvm.org/docs/ShadowCallStack.html > > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > --- > Makefile | 6 ++ > arch/Kconfig | 39 ++++++++ > include/linux/compiler-clang.h | 2 + > include/linux/compiler_types.h | 4 + > include/linux/scs.h | 88 ++++++++++++++++++ > init/init_task.c | 6 ++ > init/main.c | 3 + > kernel/Makefile | 1 + > kernel/fork.c | 9 ++ > kernel/sched/core.c | 2 + > kernel/sched/sched.h | 1 + > kernel/scs.c | 162 +++++++++++++++++++++++++++++++++ > 12 files changed, 323 insertions(+) > create mode 100644 include/linux/scs.h > create mode 100644 kernel/scs.c > > diff --git a/Makefile b/Makefile > index ffd7a912fc46..e401fa500f62 100644 > --- a/Makefile > +++ b/Makefile > @@ -846,6 +846,12 @@ ifdef CONFIG_LIVEPATCH > KBUILD_CFLAGS += $(call cc-option, -flive-patching=inline-clone) > endif > > +ifdef CONFIG_SHADOW_CALL_STACK > +KBUILD_CFLAGS += -fsanitize=shadow-call-stack > +DISABLE_SCS := -fno-sanitize=shadow-call-stack > +export DISABLE_SCS > +endif 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 ... with removal being: CFLAGS_REMOVE := $(CC_FLAGS_SCS) ... or: CFLAGS_REMOVE_obj.o := $(CC_FLAGS_SCS) That way you only need to define the flags once, so the enable and disable falgs remain in sync by construction. [...] > +config ARCH_SUPPORTS_SHADOW_CALL_STACK > + bool > + help > + An architecture should select this if it supports Clang's Shadow > + Call Stack, has asm/scs.h, and implements runtime support for shadow > + stack switching. > + > +config SHADOW_CALL_STACK_VMAP > + def_bool n A bool is default n, so you can just say bool here. > + depends on SHADOW_CALL_STACK > + help > + Use virtually mapped shadow call stacks. Selecting this option > + provides better stack exhaustion protection, but increases per-thread > + memory consumption as a full page is allocated for each shadow stack. > + > +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? > +config ROP_PROTECTION_NONE > + bool "None" IIUC this is for the benefit of the kretprobes Kconfig. 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. > +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? [...] > +#define SCS_GFP (GFP_KERNEL | __GFP_ZERO) Normally GFP_ is a prefix. For consistency, GFP_SCS would be preferable. > +extern unsigned long init_shadow_call_stack[]; Do we need this exposed here? IIUC this is only assigned by assembly in arch code. [...] > +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? Thanks, Mark.
