On Thu, Aug 27, 2020 at 2:16 PM Catalin Marinas <catalin.marinas@xxxxxxx> wrote: > > On Thu, Aug 27, 2020 at 11:56:49AM +0100, Vincenzo Frascino wrote: > > On 8/27/20 11:38 AM, Catalin Marinas wrote: > > > On Fri, Aug 14, 2020 at 07:27:06PM +0200, Andrey Konovalov wrote: > > >> diff --git a/arch/arm64/kernel/mte.c b/arch/arm64/kernel/mte.c > > >> index 7717ea9bc2a7..cfac7d02f032 100644 > > >> --- a/arch/arm64/kernel/mte.c > > >> +++ b/arch/arm64/kernel/mte.c > > >> @@ -18,10 +18,14 @@ > > >> > > >> #include <asm/barrier.h> > > >> #include <asm/cpufeature.h> > > >> +#include <asm/kasan.h> > > >> +#include <asm/kprobes.h> > > >> #include <asm/mte.h> > > >> #include <asm/ptrace.h> > > >> #include <asm/sysreg.h> > > >> > > >> +u64 gcr_kernel_excl __read_mostly; > > > > > > Could we make this __ro_after_init? > > > > Yes, it makes sense, it should be updated only once through mte_init_tags(). > > > > Something to consider though here is that this might not be the right approach > > if in future we want to add stack tagging. In such a case we need to know the > > kernel exclude mask before any C code is executed. Initializing the mask via > > mte_init_tags() it is too late. > > It depends on how stack tagging ends up in the kernel, whether it uses > ADDG/SUBG or not. If it's only IRG, I think it can cope with changing > the GCR_EL1.Excl in the middle of a function. > > > I was thinking to add a compilation define instead of having gcr_kernel_excl in > > place. This might not work if the kernel excl mask is meant to change during the > > execution. > > A macro with the default value works for me. That's what it basically is > currently, only that it ends up in a variable. Some thoughts on the topic: gcr_kernel_excl is currently initialized in mte_init_tags() and depends on the max_tag value dynamically provided to it, so it's not something that can be expressed with a define. In the case of KASAN the max_tag value is static, but if we rely on that we make core MTE code depend on KASAN, which doesn't seem right from the design perspective.
