Re: [PATCH] crypto: arm64/sha: fix function types

[Sami Tolvanen <samitolvanen@google.com>]

On Wed, Nov 13, 2019 at 12:04 PM Eric Biggers <ebiggers@kernel.org> wrote:
>
> On Tue, Nov 12, 2019 at 02:30:46PM -0800, Sami Tolvanen wrote:
> > Declare assembly functions with the expected function type
> > instead of casting pointers in C to avoid type mismatch failures
> > with Control-Flow Integrity (CFI) checking.
> >
> > Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
> > ---
> >  arch/arm64/crypto/sha1-ce-glue.c   | 12 +++++-------
> >  arch/arm64/crypto/sha2-ce-glue.c   | 26 +++++++++++---------------
> >  arch/arm64/crypto/sha256-glue.c    | 30 ++++++++++++------------------
> >  arch/arm64/crypto/sha512-ce-glue.c | 23 ++++++++++-------------
> >  arch/arm64/crypto/sha512-glue.c    | 13 +++++--------
> >  5 files changed, 43 insertions(+), 61 deletions(-)
> >
> > diff --git a/arch/arm64/crypto/sha1-ce-glue.c b/arch/arm64/crypto/sha1-ce-glue.c
> > index bdc1b6d7aff7..3153a9bbb683 100644
> > --- a/arch/arm64/crypto/sha1-ce-glue.c
> > +++ b/arch/arm64/crypto/sha1-ce-glue.c
> > @@ -25,7 +25,7 @@ struct sha1_ce_state {
> >       u32                     finalize;
> >  };
> >
> > -asmlinkage void sha1_ce_transform(struct sha1_ce_state *sst, u8 const *src,
> > +asmlinkage void sha1_ce_transform(struct sha1_state *sst, u8 const *src,
> >                                 int blocks);
>
> Please update the comments in the corresponding assembly files too.
>
> Also, this change doesn't really make sense because the assembly functions still
> expect struct sha1_ce_state, and they access sha1_ce_state::finalize which is
> not present in struct sha1_state.  There should either be wrapper functions that
> explicitly do the cast from sha1_state to sha1_ce_state, or there should be
> comments in the assembly files that very clearly explain that although the
> function prototype takes sha1_state, it's really assumed to be a sha1_ce_state.

Agreed, this needs a comment explaining the type mismatch. I'm also
fine with using wrapper functions and explicitly casting the
parameters instead of changing function declarations. Herbert, Ard,
any preferences?

Sami