linux-kernel - Re: [PATCH v4 00/45] x86: Kernel IBT

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Date:   Thu, 10 Mar 2022 17:29:11 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com,
        linux-kernel@...r.kernel.org, ndesaulniers@...gle.com,
        keescook@...omium.org, samitolvanen@...gle.com,
        mark.rutland@....com, alyssa.milburn@...el.com, mbenes@...e.cz,
        rostedt@...dmis.org, mhiramat@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v4 00/45] x86: Kernel IBT

On Thu, Mar 10, 2022 at 02:47:18PM +0100, Peter Zijlstra wrote:
> On Thu, Mar 10, 2022 at 10:35:32AM +0100, Peter Zijlstra wrote:
> 
> > > $ test_progs -t fentry
> > > test_fentry_fexit:PASS:fentry_skel_load 0 nsec
> > > test_fentry_fexit:PASS:fexit_skel_load 0 nsec
> > > test_fentry_fexit:PASS:fentry_attach 0 nsec
> > > test_fentry_fexit:FAIL:fexit_attach unexpected error: -1 (errno 19)
> > > #54 fentry_fexit:FAIL
> 
> This seems to cure the above. fexit_bpf2bpf is still failing, I'll dig
> into that after lunch.
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index acb50fb7ed2d..2d86d3c09d64 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5354,6 +5381,11 @@ int modify_ftrace_direct(unsigned long ip,
>  	mutex_lock(&direct_mutex);
>  
>  	mutex_lock(&ftrace_lock);
> +
> +	ip = ftrace_location(ip);
> +	if (!ip)
> +		goto out_unlock;
> +
>  	entry = find_direct_entry(&ip, &rec);
>  	if (!entry)
>  		goto out_unlock;

This seems to cure most of the rest. I'm still seeing one failure:

libbpf: prog 'connect_v4_prog': BPF program load failed: Invalid argument
libbpf: failed to load program 'connect_v4_prog'
libbpf: failed to load object './connect4_prog.o'
test_fexit_bpf2bpf_common:FAIL:tgt_prog_load unexpected error: -22 (errno 22)
#48/4 fexit_bpf2bpf/func_replace_verify:FAIL

but the rest seems to be good again.

diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index 2b1e266ff95c..3fecfe8c4429 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -384,6 +395,13 @@ int bpf_arch_text_poke(void *ip, enum bpf_text_poke_type t,
 		/* BPF poking in modules is not supported */
 		return -EINVAL;
 
+	/*
+	 * See emit_prologue(), for IBT builds the trampoline hook is preceded
+	 * with an ENDBR instruction.
+	 */
+	if (is_endbr(*(u32 *)ip))
+		ip += ENDBR_INSN_SIZE;
+
 	return __bpf_arch_text_poke(ip, t, old_addr, new_addr, true);
 }