Re: [PATCH v2] ubsan: Avoid i386 UBSAN handler crashes with Clang

[Justin Stitt]

Hi,

On Wed, Apr 24, 2024 at 03:40:29PM -0700, Kees Cook wrote:
> When generating Runtime Calls, Clang doesn't respect the -mregparm=3
> option used on i386. Hopefully this will be fixed correctly in Clang 19:
> https://github.com/llvm/llvm-project/pull/89707
> but we need to fix this for earlier Clang versions today. Force the
> calling convention to use non-register arguments.
> 
> Reported-by: Erhard Furtner <erhard_f@xxxxxxxxxxx>
> Closes: https://github.com/KSPP/linux/issues/350
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
> Cc: Marco Elver <elver@xxxxxxxxxx>
> Cc: Andrey Konovalov <andreyknvl@xxxxxxxxx>
> Cc: Andrey Ryabinin <ryabinin.a.a@xxxxxxxxx>
> Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> Cc: Bill Wendling <morbo@xxxxxxxxxx>
> Cc: Justin Stitt <justinstitt@xxxxxxxxxx>
> Cc: llvm@xxxxxxxxxxxxxxx
> Cc: kasan-dev@xxxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx
>  v2:
>    - use email address in Reported-by
>    - link to upstream llvm bug in ubsan.h comment
>    - drop needless /**/
>    - explicitly test Clang version
>  v1: https://lore.kernel.org/lkml/20240424162942.work.341-kees@xxxxxxxxxx/
> ---
>  lib/ubsan.h | 41 +++++++++++++++++++++++++++--------------
>  1 file changed, 27 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/ubsan.h b/lib/ubsan.h
> index 50ef50811b7c..07e37d4429b4 100644
> --- a/lib/ubsan.h
> +++ b/lib/ubsan.h
> @@ -124,19 +124,32 @@ typedef s64 s_max;
>  typedef u64 u_max;
>  #endif
>  
> -void __ubsan_handle_add_overflow(void *data, void *lhs, void *rhs);
> -void __ubsan_handle_sub_overflow(void *data, void *lhs, void *rhs);
> -void __ubsan_handle_mul_overflow(void *data, void *lhs, void *rhs);
> -void __ubsan_handle_negate_overflow(void *_data, void *old_val);
> -void __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs);
> -void __ubsan_handle_type_mismatch(struct type_mismatch_data *data, void *ptr);
> -void __ubsan_handle_type_mismatch_v1(void *_data, void *ptr);
> -void __ubsan_handle_out_of_bounds(void *_data, void *index);
> -void __ubsan_handle_shift_out_of_bounds(void *_data, void *lhs, void *rhs);
> -void __ubsan_handle_builtin_unreachable(void *_data);
> -void __ubsan_handle_load_invalid_value(void *_data, void *val);
> -void __ubsan_handle_alignment_assumption(void *_data, unsigned long ptr,
> -					 unsigned long align,
> -					 unsigned long offset);
> +/*
> + * When generating Runtime Calls, Clang doesn't respect the -mregparm=3
> + * option used on i386: https://github.com/llvm/llvm-project/issues/89670
> + * Fix this for earlier Clang versions by forcing the calling convention
> + * to use non-register arguments.
> + */
> +#if defined(CONFIG_X86_32) && \
> +    defined(CONFIG_CC_IS_CLANG) && CONFIG_CLANG_VERSION < 190000
> +# define ubsan_linkage asmlinkage

Clever.

Acked-by: Justin Stitt <justinstitt@xxxxxxxxxx>

> +#else
> +# define ubsan_linkage
> +#endif
> +
> +void ubsan_linkage __ubsan_handle_add_overflow(void *data, void *lhs, void *rhs);
> +void ubsan_linkage __ubsan_handle_sub_overflow(void *data, void *lhs, void *rhs);
> +void ubsan_linkage __ubsan_handle_mul_overflow(void *data, void *lhs, void *rhs);
> +void ubsan_linkage __ubsan_handle_negate_overflow(void *_data, void *old_val);
> +void ubsan_linkage __ubsan_handle_divrem_overflow(void *_data, void *lhs, void *rhs);
> +void ubsan_linkage __ubsan_handle_type_mismatch(struct type_mismatch_data *data, void *ptr);
> +void ubsan_linkage __ubsan_handle_type_mismatch_v1(void *_data, void *ptr);
> +void ubsan_linkage __ubsan_handle_out_of_bounds(void *_data, void *index);
> +void ubsan_linkage __ubsan_handle_shift_out_of_bounds(void *_data, void *lhs, void *rhs);
> +void ubsan_linkage __ubsan_handle_builtin_unreachable(void *_data);
> +void ubsan_linkage __ubsan_handle_load_invalid_value(void *_data, void *val);
> +void ubsan_linkage __ubsan_handle_alignment_assumption(void *_data, unsigned long ptr,
> +						       unsigned long align,
> +						       unsigned long offset);
>  
>  #endif
> -- 
> 2.34.1
> 

Thanks
Justin