Re: [PATCH bpf v2] selftests/bpf: Fix "missing ENDBR" BUG for destructor kfunc

Jiri Olsa
2022-11-27T21:59:01Z

On Fri, Nov 25, 2022 at 09:28:28PM +0800, Chen, Hu1 wrote:
> On 11/22/2022 9:48 PM, Jiri Olsa wrote:
> > On Mon, Nov 21, 2022 at 11:32:43PM -0800, Chen Hu wrote:
> >> With CONFIG_X86_KERNEL_IBT enabled, the test_verifier triggers the
> >> following BUG:
> >>
> >> traps: Missing ENDBR: bpf_kfunc_call_test_release+0x0/0x30
> >> ------------[ cut here ]------------
> >> kernel BUG at arch/x86/kernel/traps.c:254!
> >> invalid opcode: 0000 [#1] PREEMPT SMP
> >> <TASK>
> >> asm_exc_control_protection+0x26/0x50
> >> RIP: 0010:bpf_kfunc_call_test_release+0x0/0x30
> >> Code: 00 48 c7 c7 18 f2 e1 b4 e8 0d ca 8c ff 48 c7 c0 00 f2 e1 b4 c3
> >> 0f 1f 44 00 00 66 0f 1f 00 0f 1f 44 00 00 0f 0b 31 c0 c3 66 90
> >> <66> 0f 1f 00 0f 1f 44 00 00 48 85 ff 74 13 4c 8d 47 18 b8 ff ff ff
> >> bpf_map_free_kptrs+0x2e/0x70
> >> array_map_free+0x57/0x140
> >> process_one_work+0x194/0x3a0
> >> worker_thread+0x54/0x3a0
> >> ? rescuer_thread+0x390/0x390
> >> kthread+0xe9/0x110
> >> ? kthread_complete_and_exit+0x20/0x20
> >>
> >> This is because there are no compile-time references to the destructor
> >> kfuncs, bpf_kfunc_call_test_release() for example. So objtool marked
> >> them sealable and ENDBR in the functions were sealed (converted to NOP)
> >> by apply_ibt_endbr().
> >>
> >> This fix creates dummy compile-time references to destructor kfuncs so
> >> ENDBR stay there.
> >>
> >> Fixes: 05a945deefaa ("selftests/bpf: Add verifier tests for kptr")
> >> Signed-off-by: Chen Hu <hu1.chen@intel.com>
> >> Tested-by: Pengfei Xu <pengfei.xu@intel.com>
> >> ---
> >> v2:
> >> - Use generic macro name and place the macro after function body as
> >> - suggested by Jiri Olsa
> >>
> >> v1: https://lore.kernel.org/all/20221121085113.611504-1-hu1.chen@intel.com/
> >>
> >> include/linux/btf_ids.h | 7 +++++++
> >> net/bpf/test_run.c | 4 ++++
> >> 2 files changed, 11 insertions(+)
> >>
> >> diff --git a/include/linux/btf_ids.h b/include/linux/btf_ids.h
> >> index 2aea877d644f..db02691b506d 100644
> >> --- a/include/linux/btf_ids.h
> >> +++ b/include/linux/btf_ids.h
> >> @@ -266,4 +266,11 @@ MAX_BTF_TRACING_TYPE,
> >>
> >> extern u32 btf_tracing_ids[];
> >>
> >> +#if defined(CONFIG_X86_KERNEL_IBT) && !defined(__DISABLE_EXPORTS)
> >> +#define FUNC_IBT_NOSEAL(name) \
> >> + asm(IBT_NOSEAL(#name));
> >> +#else
> >> +#define FUNC_IBT_NOSEAL(name)
> >> +#endif /* CONFIG_X86_KERNEL_IBT */
> >
> > hum, IBT_NOSEAL is x86 specific, so this will probably fail build
> > on other archs.. I think we could ifdef it with CONFIG_X86, but
> > it should go to some IBT related header? surely not to btf_ids.h
> >
> > cc-ing Peter and Josh
> >
> > thanks,
> > jirka
> >
>
> The lkp reports build success because X86_KERNEL_IBT alredy depends on
> X86_64.

ah right, so please just move it to some other header

jirka

>
> Currently, arch/x86/include/asm/ibt.h which defines macro IBT_NOSEAL is
> x86 specific. How about we just put asm at test_run.c directly (ugly?):
>
> #if defined(CONFIG_X86_KERNEL_IBT) && !defined(__DISABLE_EXPORTS)
> asm(IBT_NOSEAL("bpf_kfunc_call_test_release"));
> asm(IBT_NOSEAL("bpf_kfunc_call_memb_release"));
> #endif
>
> thanks
> Chen Hu
>
> >
> >> +
> >> #endif
> >> diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
> >> index 13d578ce2a09..07263b7cc12d 100644
> >> --- a/net/bpf/test_run.c
> >> +++ b/net/bpf/test_run.c
> >> @@ -597,10 +597,14 @@ noinline void bpf_kfunc_call_test_release(struct prog_test_ref_kfunc *p)
> >> refcount_dec(&p->cnt);
> >> }
> >>
> >> +FUNC_IBT_NOSEAL(bpf_kfunc_call_test_release)
> >> +
> >> noinline void bpf_kfunc_call_memb_release(struct prog_test_member *p)
> >> {
> >> }
> >>
> >> +FUNC_IBT_NOSEAL(bpf_kfunc_call_memb_release)
> >> +
> >> noinline void bpf_kfunc_call_memb1_release(struct prog_test_member1 *p)
> >> {
> >> WARN_ON_ONCE(1);
> >> --
> >> 2.34.1
> >>