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

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Message-ID: <20220317202741.GP8939@worktop.programming.kicks-ass.net>
Date:   Thu, 17 Mar 2022 21:27:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Kumar Kartikeya Dwivedi <memxor@...il.com>,
        X86 ML <x86@...nel.org>, joao@...rdrivepizza.com,
        hjl.tools@...il.com, Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Sami Tolvanen <samitolvanen@...gle.com>,
        Mark Rutland <mark.rutland@....com>, alyssa.milburn@...el.com,
        Miroslav Benes <mbenes@...e.cz>,
        Steven Rostedt <rostedt@...dmis.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>, bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH v4 00/45] x86: Kernel IBT

On Tue, Mar 15, 2022 at 11:26:10AM -0700, Alexei Starovoitov wrote:
> The bpf trampoline can attach to both indirect and non-indirect
> functions. My understanding is that only indirect targets will have
> endbr first insn. So the fix totally makes sense.

Correct, the compiler is free to not emit endbr if it can determine the
function will never be called indirectly (or it is explicitly marked so
with a function attribute).