From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EA1092FB612; Mon, 25 Aug 2025 14:26:03 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756131964; cv=none; b=licG/yNhsMZ9wa4D7gqQHjITNRQl+LLA40P018STIvYwjFp643xXdPRR4OnMaGrs/SDxReHwJJk9Q7KXY278073ZCrZpa3h/JvbL3e5XPKjwwn9mz3YFfPRrhaa1Rb8P5d5vJESP7WoXTuIMAddGrMlnmekX2/oc1YK07/OpUI4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1756131964; c=relaxed/simple; bh=HivC8e+d4y482Da6cYyudQLG75+xG2H1Zq0+IirdkmE=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=TzroF7S0OeJgwfvQ/C3DExQVJjGIp3sEDG4RJGTScblOjAzol0dzJfVC3cszmNz1HDidh7EMdRGRe2OhJ+4yHfoGPtOr8mW09hsfJWqrl3wur9OuOZA6AyXpl9YLpgz98FcbpctCVmANiTmoYnkcncKw4AovhjsUzg36wSVbd4g= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=pjNfH8WK; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="pjNfH8WK" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A2968C116D0; Mon, 25 Aug 2025 14:26:03 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1756131963; bh=HivC8e+d4y482Da6cYyudQLG75+xG2H1Zq0+IirdkmE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pjNfH8WK7wwlxCDAwwhjnZU752SGmoD2ubuqmodGNyfTJWeONXLewWOxmik1Y5Vls Bc1dheonE3xufvqgfq7BafYodPq5cOFqWkU79VouuWmFze6QMUf8FTpcm7MJ81LJ4s W5XA+St1iUJ6JGhbM6fdEezFqE0b87qoXhtrkzi5yRg4tKA6whQsgOXnOArjXjiJQm 7OCNj4lYaJ2wPGgePFGihoTH/pDceapGb7AkfDsDx0OgcftbRadjjunHkNT1UtDvzp QxqRlRLPPuWA9WkzfjE8H9hfNUYXK6aZW9J8mlAZyQ7lprpLGwyLkXQPFGTTV2c4rC B2xrp+uNa9IiA== From: Kees Cook To: Peter Zijlstra Cc: Kees Cook , Kees Cook , David Woodhouse , Sami Tolvanen , Linus Walleij , Mark Rutland , Puranjay Mohan , Jonathan Corbet , Nathan Chancellor , x86@kernel.org, linux-doc@vger.kernel.org, linux-kbuild@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-riscv@lists.infradead.org, llvm@lists.linux.dev, linux-hardening@vger.kernel.org Subject: [PATCH 4/5] x86/cfi: Remove __noinitretpoline and __noretpoline Date: Mon, 25 Aug 2025 07:25:51 -0700 Message-Id: <20250825142603.1907143-4-kees@kernel.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20250825141316.work.967-kees@kernel.org> References: <20250825141316.work.967-kees@kernel.org> Precedence: bulk X-Mailing-List: llvm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Kees Cook Commit 66f793099a63 ("x86/retpoline: Avoid retpolines for built-in __init functions") disabled retpolines in __init sections (__noinitretpoline) as a precaution against potential issues with retpolines in early boot, but it has not been a problem in practice (i.e. see Clang below). Commit 87358710c1fb ("x86/retpoline: Support retpoline builds with Clang") narrowed this to only GCC, as Clang doesn't have per-function control over retpoline emission. As such, Clang has been booting with retpolines in __init since retpoline support was introduced. Clang KCFI has been instrumenting __init since CFI was introduced. With the introduction of KCFI for GCC, KCFI instrumentation with retpolines disabled means that objtool does not construct .retpoline_sites section entries for the non-retpoline KCFI calls. At boot, the KCFI rehashing code, via __apply_fineibt(), misses all __init KCFI calls (since they are not retpolines), resulting in immediate hash mismatches: all preambles are rehashed (via .cfi_sites) and none of the __init call sites are rehashed. Remove __noinitretpoline since it provides no meaningful utility and creates problems with CFI. Additionally remove __noretpoline since it is now unused. Alternatively, cfi_rand_callers() could walk the .kcfi_traps section which is exactly the list of KCFI instrumentation sites. But it seems better to have as few differences in common instruction sequences between compilers as possible, so better to remove the special handling of retpolines in __init for GCC. Signed-off-by: Kees Cook --- Cc: David Woodhouse --- include/linux/compiler-gcc.h | 4 ---- include/linux/init.h | 8 -------- 2 files changed, 12 deletions(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index 5d07c469b571..5de824a0b3d7 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -35,10 +35,6 @@ (typeof(ptr)) (__ptr + (off)); \ }) -#ifdef CONFIG_MITIGATION_RETPOLINE -#define __noretpoline __attribute__((__indirect_branch__("keep"))) -#endif - #if defined(LATENT_ENTROPY_PLUGIN) && !defined(__CHECKER__) #define __latent_entropy __attribute__((latent_entropy)) #endif diff --git a/include/linux/init.h b/include/linux/init.h index a60d32d227ee..17c1bc712e23 100644 --- a/include/linux/init.h +++ b/include/linux/init.h @@ -7,13 +7,6 @@ #include #include -/* Built-in __init functions needn't be compiled with retpoline */ -#if defined(__noretpoline) && !defined(MODULE) -#define __noinitretpoline __noretpoline -#else -#define __noinitretpoline -#endif - /* These macros are used to mark some functions or * initialized data (doesn't apply to uninitialized data) * as `initialization' functions. The kernel can take this @@ -50,7 +43,6 @@ /* These are for everybody (although not all archs will actually discard it in modules) */ #define __init __section(".init.text") __cold __latent_entropy \ - __noinitretpoline \ __no_kstack_erase #define __initdata __section(".init.data") #define __initconst __section(".init.rodata") -- 2.34.1