[PATCH] riscv: Disable KSAN_SANITIZE for vDSO

[Palmer Dabbelt]

On Tue, 16 Feb 2021 09:33:05 PST (-0800), tklauser at distanz.ch wrote:
> Dmitry Vyukov reports:
>> I've localized one issue with riscv/KASAN:
>> KASAN breaks VDSO and that's I think the root cause of weird faults I
>> saw earlier. The following patch fixes it.
>> Could somebody please upstream this fix? I don't know how to add/run
>> tests for this.
>
> Verified the fix on a kernel with KASAN enabled using vDSO selftests.
>
> Link: https://lore.kernel.org/lkml/CACT4Y+ZNJBnkKHXUf=tm_yuowvZvHwN=0rmJ=7J+xFd+9r_6pQ@mail.gmail.com/
> Cc: Dmitry Vyukov <dvyukov at google.com>
> Tested-by: Tobias Klauser <tklauser at distanz.ch>
> Signed-off-by: Tobias Klauser <tklauser at distanz.ch>
> ---
>  arch/riscv/kernel/vdso/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/riscv/kernel/vdso/Makefile b/arch/riscv/kernel/vdso/Makefile
> index 0cfd6da784f8..71a315e73cbe 100644
> --- a/arch/riscv/kernel/vdso/Makefile
> +++ b/arch/riscv/kernel/vdso/Makefile
> @@ -32,9 +32,10 @@ CPPFLAGS_vdso.lds += -P -C -U$(ARCH)
>  # Disable -pg to prevent insert call site
>  CFLAGS_REMOVE_vgettimeofday.o = $(CC_FLAGS_FTRACE) -Os
>
> -# Disable gcov profiling for VDSO code
> +# Disable profiling and instrumentation for VDSO code
>  GCOV_PROFILE := n
>  KCOV_INSTRUMENT := n
> +KASAN_SANITIZE := n
>
>  # Force dependency
>  $(obj)/vdso.o: $(obj)/vdso.so

This seems reasonable.  Building the VDSO with asan results in a bunch of PLT
entries for the VDSO stubs.  I don't see a sane way to resolve those, and it
looks like this is what everyone else is doing.

That said, the commit text is a bit funny so I've written one of my own.  This
is on for-next, as it's still the merge window.  Let me know if the text
doesn't make sense.

Thanks!