From nobody Sun Feb 8 14:56:52 2026 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (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 22B4826E62C; Wed, 26 Feb 2025 10:54:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740567266; cv=none; b=EPchBH9FG30iNceNVNljdjy9sKY0VkiacYOJzjGo/+GhO/Wex3AIJ9pe819U2yrt0R63sl0p1186xeGUMagMcycR+aw7pJ4zca/vxL15b255B/j920XcI6GOwH7V21QlEDVveL1XGnifo5v8Hf8TOrT2fQoOzC7ca7NGf7Quh64= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1740567266; c=relaxed/simple; bh=9jQi2oe4ACPxFgTZT/wfimYgKbuAA934twTRiC/0+M0=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=NEf3iovxdQwVNoj1Y7Rr90Bx9MocixgO96k1CI3JMdAe+Gdx21jdo3ydIIi/xQ/keCmRkicWT5HGbxj1pEwP7R4G8y98WnfZJo+lX4hiGDpkejI+qHUqZU3UfTm0IGj8kSTMBDzL6K3OHGSIwZFShQFzDX1SPra1LPoR6If/3jU= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=XUex2nyZ; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=rT0E5ANI; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="XUex2nyZ"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="rT0E5ANI" Date: Wed, 26 Feb 2025 10:54:21 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1740567261; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1pdqb2IAcYHElMsrgqXtnTLk+Cj80ClKr57N3fKBXUw=; b=XUex2nyZyAhFFiQP5854Ja7X5G5iEemjl6xnqVhIWo8xZMDyLuKx5zCdGgxbIRZlWTS7rf ezmaSazyWewEwel5ASYumOAdlYPhMdfW26p2TBbYOZJl+kB8QsTS81NG1Xo/1BFMzihskU FCua+yOJby4mfRdODOdS2MUoVA320IUpF5aDaeyHXLADcUP4HIWXMV/aJvxu0S83ArwabX S8qUxQenrprUDVUORYOQ+IrAaO0qK6N6knOJdp4tKiqvo6kmLKS967YeFbR1p3XNujfm82 1ohSPfHGySMNgBhVPq9JkiiSzhxe3wigxPp185s2ZlJyz0zOykbjToBFcmnx7g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1740567261; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=1pdqb2IAcYHElMsrgqXtnTLk+Cj80ClKr57N3fKBXUw=; b=rT0E5ANI9m0c40Am56qXCbgS7XqdeLovJ9UunSZaDFXlkh0ZGmKse4D6OKVsNYDmygT1OO Ln8GScduK+3TdxCA== From: "tip-bot2 for Peter Zijlstra" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/core] x86/ibt: Optimize FineIBT sequence Cc: Scott Constable , "Peter Zijlstra (Intel)" , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20250224124200.371942555@infradead.org> References: <20250224124200.371942555@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <174056726115.10177.145025681668547446.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Precedence: bulk Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable The following commit has been merged into the x86/core branch of tip: Commit-ID: 7359ea8e1b7fbd5b98cb72a9f596ddf67f2dc33b Gitweb: https://git.kernel.org/tip/7359ea8e1b7fbd5b98cb72a9f596ddf67= f2dc33b Author: Peter Zijlstra AuthorDate: Mon, 24 Feb 2025 13:37:08 +01:00 Committer: Peter Zijlstra CommitterDate: Wed, 26 Feb 2025 11:41:54 +01:00 x86/ibt: Optimize FineIBT sequence Scott notes that non-taken branches are faster. Abuse overlapping code that traps instead of explicit UD2 instructions. And LEA does not modify flags and will have less dependencies. Suggested-by: Scott Constable Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Kees Cook Link: https://lore.kernel.org/r/20250224124200.371942555@infradead.org --- arch/x86/kernel/alternative.c | 61 ++++++++++++++++++++++------------ arch/x86/net/bpf_jit_comp.c | 5 +-- 2 files changed, 42 insertions(+), 24 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 1cc0e4d..599f218 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -1053,9 +1053,9 @@ early_param("cfi", cfi_parse_cmdline); * __cfi_\func: __cfi_\func: * movl $0x12345678,%eax // 5 endbr64 // 4 * nop subl $0x12345678,%r10d // 7 - * nop jz 1f // 2 - * nop ud2 // 2 - * nop 1: nop // 1 + * nop jne __cfi_\func+6 // 2 + * nop nop3 // 3 + * nop * nop * nop * nop @@ -1067,37 +1067,50 @@ early_param("cfi", cfi_parse_cmdline); * * caller: caller: * movl $(-0x12345678),%r10d // 6 movl $0x12345678,%r10d // 6 - * addl $-15(%r11),%r10d // 4 sub $16,%r11 // 4 + * addl $-15(%r11),%r10d // 4 lea -0x10(%r11),%r11 // 4 * je 1f // 2 nop4 // 4 * ud2 // 2 - * 1: call __x86_indirect_thunk_r11 // 5 call *%r11; nop2; // 5 + * 1: cs call __x86_indirect_thunk_r11 // 6 call *%r11; nop3; // 6 * */ =20 -asm( ".pushsection .rodata \n" - "fineibt_preamble_start: \n" - " endbr64 \n" - " subl $0x12345678, %r10d \n" - " je fineibt_preamble_end \n" - "fineibt_preamble_ud2: \n" - " ud2 \n" - " nop \n" - "fineibt_preamble_end: \n" +/* + * : + * 0: f3 0f 1e fa endbr64 + * 4: 41 81 78 56 34 12 sub $0x12345678, %r10d + * b: 75 f9 jne 6 + * d: 0f 1f 00 nopl (%rax) + * + * Note that the JNE target is the 0xEA byte inside the SUB, this decodes = as + * (bad) on x86_64 and raises #UD. + */ +asm( ".pushsection .rodata \n" + "fineibt_preamble_start: \n" + " endbr64 \n" + " subl $0x12345678, %r10d \n" + " jne fineibt_preamble_start+6 \n" + ASM_NOP3 + "fineibt_preamble_end: \n" ".popsection\n" ); =20 extern u8 fineibt_preamble_start[]; -extern u8 fineibt_preamble_ud2[]; extern u8 fineibt_preamble_end[]; =20 #define fineibt_preamble_size (fineibt_preamble_end - fineibt_preamble_sta= rt) -#define fineibt_preamble_ud2 (fineibt_preamble_ud2 - fineibt_preamble_sta= rt) +#define fineibt_preamble_ud 6 #define fineibt_preamble_hash 7 =20 +/* + * : + * 0: 41 ba 78 56 34 12 mov $0x12345678, %r10d + * 6: 4d 8d 5b f0 lea -0x10(%r11), %r11 + * a: 0f 1f 40 00 nopl 0x0(%rax) + */ asm( ".pushsection .rodata \n" "fineibt_caller_start: \n" " movl $0x12345678, %r10d \n" - " sub $16, %r11 \n" + " lea -0x10(%r11), %r11 \n" ASM_NOP4 "fineibt_caller_end: \n" ".popsection \n" @@ -1428,15 +1441,15 @@ static void poison_cfi(void *addr) } =20 /* - * regs->ip points to a UD2 instruction, return true and fill out target a= nd - * type when this UD2 is from a FineIBT preamble. + * When regs->ip points to a 0xEA byte in the FineIBT preamble, + * return true and fill out target and type. * * We check the preamble by checking for the ENDBR instruction relative to= the - * UD2 instruction. + * 0xEA instruction. */ bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 = *type) { - unsigned long addr =3D regs->ip - fineibt_preamble_ud2; + unsigned long addr =3D regs->ip - fineibt_preamble_ud; u32 hash; =20 if (!exact_endbr((void *)addr)) @@ -1447,6 +1460,12 @@ bool decode_fineibt_insn(struct pt_regs *regs, unsig= ned long *target, u32 *type) __get_kernel_nofault(&hash, addr + fineibt_preamble_hash, u32, Efault); *type =3D (u32)regs->r10 + hash; =20 + /* + * Since regs->ip points to the middle of an instruction; it cannot + * continue with the normal fixup. + */ + regs->ip =3D *target; + return true; =20 Efault: diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index f36508b..ce033e6 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -417,9 +417,8 @@ static void emit_fineibt(u8 **pprog, u32 hash) =20 EMIT_ENDBR(); EMIT3_off32(0x41, 0x81, 0xea, hash); /* subl $hash, %r10d */ - EMIT2(0x74, 0x07); /* jz.d8 +7 */ - EMIT2(0x0f, 0x0b); /* ud2 */ - EMIT1(0x90); /* nop */ + EMIT2(0x75, 0xf9); /* jne.d8 .-7 */ + EMIT3(0x0f, 0x1f, 0x00); /* nop3 */ EMIT_ENDBR_POISON(); =20 *pprog =3D prog;