Re: [PATCH] sparc: vdso: Disable UBSAN instrumentation

[Sam Ravnborg]

Hi Kees,

On Fri, Feb 23, 2024 at 08:59:45AM -0800, Kees Cook wrote:
> The UBSAN instrumentation cannot work in the vDSO since it is executing
> in userspace, so disable it in the Makefile. Fixes the build failures
> such as:
> 
> arch/sparc/vdso/vclock_gettime.c:217: undefined reference to `__ubsan_handle_shift_out_of_bounds'
> 
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Andreas Larsson <andreas@xxxxxxxxxxx>
> Cc: Masahiro Yamada <masahiroy@xxxxxxxxxx>
> Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
> Cc: Helge Deller <deller@xxxxxx>
> Cc: Guo Ren <guoren@xxxxxxxxxx>
> Cc: sparclinux@xxxxxxxxxxxxxxx
> ---
>  arch/sparc/vdso/Makefile | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/arch/sparc/vdso/Makefile b/arch/sparc/vdso/Makefile
> index 7f5eedf1f5e0..e8aef2c8ae99 100644
> --- a/arch/sparc/vdso/Makefile
> +++ b/arch/sparc/vdso/Makefile
> @@ -2,6 +2,7 @@
>  #
>  # Building vDSO images for sparc.
>  #
> +UBSAN_SANITIZE := n

When I read:

config UBSAN_SANITIZE_ALL
        bool "Enable instrumentation for the entire kernel"
        depends on ARCH_HAS_UBSAN_SANITIZE_ALL
        default y
        help
          This option activates instrumentation for the entire kernel.
          If you don't enable this option, you have to explicitly specify
          UBSAN_SANITIZE := y for the files/directories you want to check for UB.
          Enabling this option will get kernel image size increased
          significantly.


I am left with the understanding that only arch's that
selects ARCH_HAS_UBSAN_SANITIZE_ALL would need to turn off
UBSAN_SANITIZE.

Are this fix papering over some other bug where we enable
UBSAN_SANITIZE_ALL for arch's that should not have it,
or something else that enable it?

	Sam