From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <kees@kernel.org>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Nathan Chancellor <nathan@kernel.org>,
Nick Desaulniers <ndesaulniers@google.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
llvm@lists.linux.dev, linux-kernel@vger.kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check
Date: Mon, 12 Oct 2026 11:22:50 +0200 [thread overview]
Message-ID: <20261012092250.GO4121339@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20261012090436.1676525-3-kees@kernel.org>
On Mon, Oct 12, 2026 at 02:04:26AM -0700, Kees Cook wrote:
> With MITIGATION_RETPOLINE=y, GCC lowers the computed goto in
> ___bpf_prog_run() to a jump through __x86_indirect_thunk_rdx. objtool
> puts that jump on the retpoline call list along with the indirect calls,
> so with CONFIG_CFI=y the kCFI check wants a UD2 before it:
>
> vmlinux.o: warning: objtool: ___bpf_prog_run+0x1e: no-cfi indirect call!
>
> The jump goes through the "jumptable" array, which objtool already reads
> from .data.rel.ro.c_jump_table, so its targets stay inside the function
> and need no kCFI check. Skip jump table jumps in the check. Clang does
> not emit this jump: with retpolines, it lowers the computed goto without
> an indirect jump.
I am confused.. I don't see a computed goto in __bpf_prog_run(), and we
build with -fno-jump-tables.
prev parent reply other threads:[~2026-10-12 9:22 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-12 9:04 [PATCH 0/3] x86/cfi: Fix a few kCFI issues found with GCC Kees Cook
2026-10-12 9:04 ` [PATCH 1/3] x86/kcfi: Decode the kCFI check from the trap address Kees Cook
2026-10-12 9:59 ` [tip: x86/urgent] " tip-bot2 for Kees Cook
2026-10-12 9:04 ` [PATCH 2/3] x86/kcfi: Emit the FineIBT paranoid "cs" prefix as a byte Kees Cook
2026-10-12 9:16 ` Peter Zijlstra
2026-10-12 9:59 ` [tip: x86/core] " tip-bot2 for Kees Cook
2026-10-12 9:04 ` [PATCH 3/3] objtool: Skip jump table jumps in the kCFI indirect call check Kees Cook
2026-10-12 9:22 ` Peter Zijlstra [this message]
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