[PATCH] riscv: Disable KSAN_SANITIZE for vDSO

[Tobias Klauser]

On 2021-02-19 at 08:15:34 +0100, Palmer Dabbelt <palmer at dabbelt.com> wrote:
> 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 for fixing up the commit message and adding the Fixes line. Makes
sense to me.