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Message-ID: <20231208224557.GH36716@noisy.programming.kicks-ass.net> Date: Fri, 8 Dec 2023 23:45:57 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Alexei Starovoitov <alexei.starovoitov@...il.com> Cc: Jiri Olsa <olsajiri@...il.com>, Song Liu <song@...nel.org>, Song Liu <songliubraving@...a.com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>, "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Arnd Bergmann <arnd@...db.de>, Sami Tolvanen <samitolvanen@...gle.com>, Kees Cook <keescook@...omium.org>, Nathan Chancellor <nathan@...nel.org>, Nick Desaulniers <ndesaulniers@...gle.com>, linux-riscv <linux-riscv@...ts.infradead.org>, LKML <linux-kernel@...r.kernel.org>, Network Development <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>, linux-arch <linux-arch@...r.kernel.org>, clang-built-linux <llvm@...ts.linux.dev>, Josh Poimboeuf <jpoimboe@...nel.org>, Joao Moreira <joao@...rdrivepizza.com>, Mark Rutland <mark.rutland@....com> Subject: Re: [PATCH v2 2/2] x86/cfi,bpf: Fix BPF JIT call On Fri, Dec 08, 2023 at 12:58:01PM -0800, Alexei Starovoitov wrote: > On Fri, Dec 8, 2023 at 12:52 PM Peter Zijlstra <peterz@...radead.org> wrote: > > > > On Fri, Dec 08, 2023 at 12:41:03PM -0800, Alexei Starovoitov wrote: > > > On Fri, Dec 8, 2023 at 12:35 PM Peter Zijlstra <peterz@...radead.org> wrote: > > > > > > -__bpf_kfunc void bpf_task_release(struct task_struct *p) > > > > +__bpf_kfunc void bpf_task_release(void *p) > > > > > > Yeah. That won't work. We need a wrapper. > > > Since bpf prog is also calling it directly. > > > In progs/task_kfunc_common.h > > > void bpf_task_release(struct task_struct *p) __ksym; > > > > > > than later both libbpf and the verifier check that > > > what bpf prog is calling actually matches the proto > > > of what is in the kernel. > > > Effectively we're doing strong prototype check at load time. > > > > I'm still somewhat confused on how this works, where does BPF get the > > address of the function from? and what should I call the wrapper? > > It starts with > register_btf_id_dtor_kfuncs() that takes a set of btf_ids: > {btf_id_of_type, btf_id_of_dtor_function}, ... > > Then based on btf_id_of_dtor_function we find its type proto, name, do checks, > and eventually: > addr = kallsyms_lookup_name(dtor_func_name); > field->kptr.dtor = (void *)addr; > > bpf_task_release(struct task_struct *p) would need to stay as-is, > but we can have a wrapper > void bpf_task_release_dtor(void *p) > { > bpf_task_release(p); > } > > And adjust the above lookup with extra "_dtor" suffix. > > > > btw instead of EXPORT_SYMBOL_GPL(bpf_task_release) > > > can __ADDRESSABLE be used ? > > > Since it's not an export symbol. > > > > No __ADDRESSABLE() is expressly ignored, but we have IBT_NOSEAL() that > > should do it. I'll rename the thing and lift it out of x86 to avoid > > breaking all other arch builds. > > Makes sense. Ok, did that. Current patches (on top of bpf-next) are here: git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git x86/cfi (really should try and write better changelogs, but it's too late) The test_progs thing still doesn't run to completion, the next problem seems to be bpf_throw(): [ 247.720159] ? die+0xa4/0xd0 [ 247.720216] ? do_trap+0xa5/0x180 [ 247.720281] ? __cfi_bpf_prog_8ac473954ac6d431_F+0xd/0x10 [ 247.720368] ? __cfi_bpf_prog_8ac473954ac6d431_F+0xd/0x10 [ 247.720459] ? do_error_trap+0xba/0x120 [ 247.720525] ? __cfi_bpf_prog_8ac473954ac6d431_F+0xd/0x10 [ 247.720614] ? handle_invalid_op+0x2c/0x40 [ 247.720684] ? __cfi_bpf_prog_8ac473954ac6d431_F+0xd/0x10 [ 247.720775] ? exc_invalid_op+0x38/0x60 [ 247.720840] ? asm_exc_invalid_op+0x1a/0x20 [ 247.720909] ? 0xffffffffc001ba54 [ 247.720971] ? __cfi_bpf_prog_8ac473954ac6d431_F+0xd/0x10 [ 247.721063] ? bpf_throw+0x9b/0xf0 [ 247.721126] ? bpf_test_run+0x108/0x350 [ 247.721191] ? bpf_prog_5555714b685bf0cf_exception_throw_always_1+0x26/0x26 [ 247.721301] ? bpf_test_run+0x108/0x350 [ 247.721368] bpf_test_run+0x212/0x350 [ 247.721433] ? slab_build_skb+0x22/0x110 [ 247.721503] bpf_prog_test_run_skb+0x347/0x4a0 But I'm too tired to think staight. Is this a bpf_callback_t vs bpf_exception_cb difference? I'll prod more later. Zzzz..
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