On 11/2/21 9:04 PM, Szabolcs Nagy wrote:
The 11/02/2021 00:06, Dan Li via Gcc-patches wrote:
Shadow Call Stack can be used to protect the return address of a
function at runtime, and clang already supports this feature[1].
To enable SCS in user mode, in addition to compiler, other support
is also required (as described in [2]). This patch only adds basic
support for SCS from the compiler side, and provides convenience
for users to enable SCS.
For linux kernel, only the support of the compiler is required.
[1] https://clang.llvm.org/docs/ShadowCallStack.html
[2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102768
i'm not a gcc maintainer, but i prefer such feature
to be in upstream gcc instead of in a plugin.
it will require update to the documentation:
which should mention that it depends on -ffixed-x18
(probably that should be enforced too) which is an
important abi issue: functions following the normal
pcs can clobber x18 and break scs.
Thanks Szabolcs, I will update the documentation in next version.
It sounds reasonable to enforced -ffixed-x18 with scs, but I see
that clang doesn’t do that. Maybe it is better to be consistent
with clang here?
and that there is no unwinder support.
Ok, let me try to add a support for this.
the abi issue means it is unlikely to be useful in
linux user space (even if libc and unwinder support
is implemented), but it can be still useful in
freestanding code such as the linux kernel.
thanks.
