From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <kees@kernel.org>
Cc: Nathan Chancellor <nathan@kernel.org>,
Vegard Nossum <vegard.nossum@oracle.com>,
Miguel Ojeda <ojeda@kernel.org>,
Linus Walleij <linus.walleij@linaro.org>,
Jeff Johnson <jeff.johnson@oss.qualcomm.com>,
Randy Dunlap <rdunlap@infradead.org>,
David Woodhouse <dwmw2@infradead.org>,
"Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
Nick Desaulniers <nick.desaulniers+lkml@gmail.com>,
Bill Wendling <morbo@google.com>,
Justin Stitt <justinstitt@google.com>,
Marco Elver <elver@google.com>,
Przemek Kitszel <przemyslaw.kitszel@intel.com>,
Ramon de C Valle <rcvalle@google.com>,
Jonathan Corbet <corbet@lwn.net>,
"Paul E. McKenney" <paulmck@kernel.org>,
Nicolas Schier <nicolas.schier@linux.dev>,
Masahiro Yamada <masahiroy@kernel.org>,
Arnd Bergmann <arnd@arndb.de>,
Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>,
Sami Tolvanen <samitolvanen@google.com>,
Mark Rutland <mark.rutland@arm.com>,
linux-kernel@vger.kernel.org, llvm@lists.linux.dev,
linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, x86@kernel.org,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH v2 5/9] x86/cfi: Add "debug" option to "cfi=" bootparam
Date: Thu, 4 Sep 2025 09:00:35 +0200 [thread overview]
Message-ID: <20250904070035.GW4067720@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20250904034656.3670313-5-kees@kernel.org>
On Wed, Sep 03, 2025 at 08:46:44PM -0700, Kees Cook wrote:
> @@ -1734,6 +1737,8 @@ static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
> * rewrite them. This disables all CFI. If this succeeds but any of the
> * later stages fails, we're without CFI.
> */
> + if (cfi_debug)
> + pr_info("CFI: disabling all indirect call checking\n");
> ret = cfi_disable_callers(start_retpoline, end_retpoline);
> if (ret)
> goto err;
> @@ -1744,14 +1749,23 @@ static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
> cfi_bpf_hash = cfi_rehash(cfi_bpf_hash);
> cfi_bpf_subprog_hash = cfi_rehash(cfi_bpf_subprog_hash);
> }
> + if (cfi_debug)
> + pr_info("CFI: cfi_seed: 0x%08x\n", cfi_seed);
>
> + if (cfi_debug)
> + pr_info("CFI: rehashing all preambles\n");
So this repeated if() bugs the heck out of me ... :-)
What would you prefer, this:
if (cfi_debug) {
pr_info("CFI: cfi_seed: 0x%08x\n", cfi_seed);
pr_info("CFI: rehashing all preambles\n");
}
or something like:
#define pr_cfi_debug(X...) if (cfi_debug) pr_info(X)
pr_cfi_debug("CFI: cfi_seed: 0x%08x\n", cfi_seed);
pr_cfi_debug("CFI: rehashing all preambles\n");
?
> ret = cfi_rand_preamble(start_cfi, end_cfi);
> if (ret)
> goto err;
>
> + if (cfi_debug)
> + pr_info("CFI: rehashing all indirect calls\n");
> ret = cfi_rand_callers(start_retpoline, end_retpoline);
> if (ret)
> goto err;
> + } else {
> + if (cfi_debug)
> + pr_info("CFI: rehashing disabled\n");
> }
>
> switch (cfi_mode) {
> @@ -1761,6 +1775,8 @@ static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
> return;
>
> case CFI_KCFI:
> + if (cfi_debug)
> + pr_info("CFI: enabling all indirect call checking\n");
This should be "CFI: re-enabling all..." I suppose, to better match the
earlier "CFI: disabling all ..." message.
> ret = cfi_enable_callers(start_retpoline, end_retpoline);
> if (ret)
> goto err;
> @@ -1771,17 +1787,23 @@ static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
> return;
>
> case CFI_FINEIBT:
> + if (cfi_debug)
> + pr_info("CFI: adding FineIBT to all preambles\n");
> /* place the FineIBT preamble at func()-16 */
> ret = cfi_rewrite_preamble(start_cfi, end_cfi);
> if (ret)
> goto err;
>
> /* rewrite the callers to target func()-16 */
> + if (cfi_debug)
> + pr_info("CFI: rewriting indirect call sites to use FineIBT\n");
> ret = cfi_rewrite_callers(start_retpoline, end_retpoline);
> if (ret)
> goto err;
>
> /* now that nobody targets func()+0, remove ENDBR there */
> + if (cfi_debug)
> + pr_info("CFI: removing old endbr insns\n");
> cfi_rewrite_endbr(start_cfi, end_cfi);
>
> if (builtin) {
> @@ -2324,6 +2346,7 @@ void __init alternative_instructions(void)
>
> __apply_fineibt(__retpoline_sites, __retpoline_sites_end,
> __cfi_sites, __cfi_sites_end, true);
> + cfi_debug = false;
>
> /*
> * Rewrite the retpolines, must be done before alternatives since
next prev parent reply other threads:[~2025-09-04 7:00 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-04 3:46 [PATCH v2 0/9] kcfi: Prepare for GCC support Kees Cook
2025-09-04 3:46 ` [PATCH v2 1/9] compiler_types.h: Move __nocfi out of compiler-specific header Kees Cook
2025-09-04 18:28 ` Nathan Chancellor
2025-09-04 3:46 ` [PATCH v2 2/9] x86/traps: Clarify KCFI instruction layout Kees Cook
2025-09-04 3:46 ` [PATCH v2 3/9] x86/cfi: Document the "cfi=" bootparam options Kees Cook
2025-09-04 18:32 ` Nathan Chancellor
2025-09-04 3:46 ` [PATCH v2 4/9] x86/cfi: Standardize on common "CFI:" prefix for CFI reports Kees Cook
2025-09-04 18:40 ` Nathan Chancellor
2025-09-05 0:40 ` Kees Cook
2025-09-04 3:46 ` [PATCH v2 5/9] x86/cfi: Add "debug" option to "cfi=" bootparam Kees Cook
2025-09-04 7:00 ` Peter Zijlstra [this message]
2025-09-04 3:46 ` [PATCH v2 6/9] x86/cfi: Remove __noinitretpoline and __noretpoline Kees Cook
2025-09-04 3:46 ` [PATCH v2 7/9] kconfig: Add transitional symbol attribute for migration support Kees Cook
2025-09-04 3:46 ` [PATCH v2 8/9] kcfi: Rename CONFIG_CFI_CLANG to CONFIG_CFI Kees Cook
2025-09-04 3:46 ` [PATCH v2 9/9] ARM: traps: Implement KCFI trap handler for ARM32 Kees Cook
2025-09-04 7:04 ` [PATCH v2 0/9] kcfi: Prepare for GCC support Peter Zijlstra
2025-09-04 16:37 ` Kees Cook
2025-09-04 20:01 ` Peter Zijlstra
2025-09-05 0:42 ` Kees Cook
2025-09-05 7:44 ` Miguel Ojeda
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