On Sat Dec 14, 2024 at 12:55 AM CET, Eduard Zingerman wrote:
> On Fri, 2024-12-13 at 22:27 +0100, Arthur Fabre wrote:
[...]
> > +++ b/tools/testing/selftests/bpf/progs/verifier_abnormal_ret.c
> > @@ -0,0 +1,88 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +
> > +#include <linux/bpf.h>
> > +#include <bpf/bpf_helpers.h>
> > +#include "../../../include/linux/filter.h"
> > +#include "bpf_misc.h"
> > +
> > +#define TEST(NAME, CALLEE) \
> > + SEC("socket") \
> > + __description("abnormal_ret: " #NAME) \
> > + __failure __msg("math between ctx pointer and register with unbounded min value") \
> > + __naked void check_abnormal_ret_##NAME(void) \
> > + { \
>
> Nit: this one and 'callee_tail_call' could be plain C.
>
> > + asm volatile(" \
> > + r6 = r1; \
> > + call " #CALLEE "; \
> > + r6 += r0; \
> > + r0 = 0; \
> > + exit; \
> > + " : \
> > + : \
> > + : __clobber_all); \
> > + }
>
> [...]
>
> > +static __naked __noinline __used
> > +int callee_tail_call(void)
> > +{
> > + asm volatile(" \
> > + r2 = %[map_prog] ll; \
> > + r3 = 0; \
> > + call %[bpf_tail_call]; \
> > + r0 = 0; \
> > + exit; \
> > +" :
> > + : __imm(bpf_tail_call), __imm_addr(map_prog)
> > + : __clobber_all);
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
Thanks for the review! Good point, I'll try to write them in C.
It might not be possible to do them both entirely: clang also doesn't
know that bpf_tail_call() can return, so it assumes the callee() will
return a constant r0. It sometimes optimizes branches / loads out
because of this.
