On Fri, Nov 01, 2019 at 03:11:43PM -0700, Sami Tolvanen wrote: > With CONFIG_KRETPROBES, function return addresses are modified to > redirect control flow to kretprobe_trampoline. This is incompatible > with SCS. I'm a bit confused as to why that's the case -- could you please elaborate on how this is incompatible? IIUC kretrobes works by patching the function entry point with a BRK, so that it can modify the LR _before_ it is saved to the stack. I don't see how SCS affects that. When the instrumented function returns, it'll balance its SCS state, then "return" to kretprobe_trampoline. Since kretprobe_trampoline is plain assembly, it doesn't have SCS, and can modify the LR live, as it does. So functionally, that appears to work. What am I missing? Thanks, Mark. > Signed-off-by: Sami Tolvanen <samitolvanen@xxxxxxxxxx> > Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx> > --- > arch/arm64/Kconfig | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 3f047afb982c..e7b57a8a5531 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -165,7 +165,7 @@ config ARM64 > select HAVE_STACKPROTECTOR > select HAVE_SYSCALL_TRACEPOINTS > select HAVE_KPROBES > - select HAVE_KRETPROBES > + select HAVE_KRETPROBES if !SHADOW_CALL_STACK > select HAVE_GENERIC_VDSO > select IOMMU_DMA if IOMMU_SUPPORT > select IRQ_DOMAIN > -- > 2.24.0.rc1.363.gb1bccd3e3d-goog >
