On Mon, Feb 17, 2020 at 04:51:46PM +0100, Daniel Borkmann wrote: > On 1/29/20 10:36 PM, Kees Cook wrote: > > In an effort to enable -Wcast-function-type in the top-level Makefile > > to support Control Flow Integrity builds, rework the BPF instruction > > immediate calculation macros to avoid mismatched function pointers. Since > > these calculations are only ever between function address (these are > > not function calls, just address calculations), they can be cast to u64 > > instead, where the result will be assigned to the s32 insn->imm. > > > > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > > --- > > include/linux/filter.h | 6 +++--- > > kernel/bpf/hashtab.c | 6 +++--- > > kernel/bpf/verifier.c | 21 +++++++-------------- > > 3 files changed, 13 insertions(+), 20 deletions(-) > > > > diff --git a/include/linux/filter.h b/include/linux/filter.h > > index f349e2c0884c..b5beee7bf2ea 100644 > > --- a/include/linux/filter.h > > +++ b/include/linux/filter.h > > @@ -340,8 +340,8 @@ static inline bool insn_is_zext(const struct bpf_insn *insn) > > /* Function call */ > > -#define BPF_CAST_CALL(x) \ > > - ((u64 (*)(u64, u64, u64, u64, u64))(x)) > > +#define BPF_FUNC_IMM(FUNC) \ > > + ((u64)(FUNC) - (u64)__bpf_call_base) > > Looks good to me in general. My only concern is compilation on 32bit archs: I think > the cast needs to be of '(u64)(unsigned long)' to avoid introducing new warnings a la > 'cast from pointer to integer of different size'. Oh, good point. I'll double-check the 32-bit builds. (I also have another related change that I found several days later.) I'll get this adjusted/tested and resend the patch. Thanks! -Kees -- Kees Cook
