From nobody Sun Feb 8 10:29:56 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 E83925F84D; Tue, 13 Feb 2024 15:36:02 +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=1707838564; cv=none; b=pLq6iaXs7/JPiKezCwCO/DNtSF7AMdN6vfJ75cV7L/JKS1iNfjPW05jOWJl92GW8QJgAe+bAEY5carpM0ZQ6MPkpmkZSySIuSnl5zYU02XYiVCMO/kyG8Ow+qLSy5c0cIrIDFO8IpRETFmXxkIdieEx521JkRy+Z9MTFdZ9c7Jw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1707838564; c=relaxed/simple; bh=aVgoCDjaCj+eT7ageQaio+TWORvefVyEZ/TIQDNwpVg=; h=Date:From:To:Subject:Cc:In-Reply-To:References:MIME-Version: Message-ID:Content-Type; b=QK34hY5fGSMu4tCTrkd2OCJOWOhiPMGLZYnTc9lq89GeOq7cjTaiB5bFv7vTeZah0Ktxz6ptCizSH1e+Y7v1Pf+7KNaC/auPTxde6zMvhsm2vPRBpjER5A7KTwHMd81TTXHMGqKfars5EhmhvLd46kfmWbkqOJMd5XIWYyDsFYU= 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=TV6shhgJ; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=GpAt0edQ; 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="TV6shhgJ"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="GpAt0edQ" Date: Tue, 13 Feb 2024 15:36:00 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1707838561; 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=l7GypcD490unVLgueSk5Pu7RzO5BZKUqSeBYWtjlgPQ=; b=TV6shhgJ+o5v7CalaGBTctqdAELugp5pGzBhLKdPB9k6I/gGwCKvLKrORarzAodX0at6cb PebjCUYC8Tqa+ZRbohpF7Ybz3OXPsmhG4nQe7/yhZgz2/Ov6RtCsXQ5zdad1YN1Z+j7JLZ Vpwhqk4Rg8HpKEcW179pxVV5L5x1Z1kXs3iVkD11JtoNcUlSupZfWsYWkLYDLs47Cf4Lde UMNet7uX61toKHsQwnf8cQM2q05kLLxHUQ4FrRHksaQ8rJ6b8p2QEmGtZrHvoRv9XoXdWN 3PQJVODrkOVXaNRotwjpTssUuJcrJCEuVY2pgRal5PUMHbri8SLjqaXiNqFUCQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1707838561; 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=l7GypcD490unVLgueSk5Pu7RzO5BZKUqSeBYWtjlgPQ=; b=GpAt0edQmZw4UifW0dSzAsnZkBOAgeKz5FS8QW8v7h6exsoHFmNmUJ3jq7KWyqTKXOgGmG WH26GidQPg6dEQBA== From: "tip-bot2 for Borislav Petkov (AMD)" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: x86/alternatives] x86/alternatives: Use a temporary buffer when optimizing NOPs Cc: "Borislav Petkov (AMD)" , Thomas Gleixner , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20240130105941.19707-2-bp@alien8.de> References: <20240130105941.19707-2-bp@alien8.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Message-ID: <170783856041.398.6328711543597681720.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/alternatives branch of ti= p: Commit-ID: fca88864f9d5637381b71a0cd38b7f5e82eab01d Gitweb: https://git.kernel.org/tip/fca88864f9d5637381b71a0cd38b7f5e8= 2eab01d Author: Borislav Petkov (AMD) AuthorDate: Tue, 30 Jan 2024 11:59:38 +01:00 Committer: Borislav Petkov (AMD) CommitterDate: Tue, 13 Feb 2024 16:16:02 +01:00 x86/alternatives: Use a temporary buffer when optimizing NOPs Instead of optimizing NOPs in-place, use a temporary buffer like the usual alternatives patching flow does. This obviates the need to grab locks when patching, see 6778977590da ("x86/alternatives: Disable interrupts and sync when optimiz= ing NOPs in place") While at it, add nomenclature definitions clarifying and simplifying the naming of function-local variables in the alternatives code. Signed-off-by: Borislav Petkov (AMD) Acked-by: Thomas Gleixner Link: https://lore.kernel.org/r/20240130105941.19707-2-bp@alien8.de --- arch/x86/kernel/alternative.c | 78 ++++++++++++++++++---------------- 1 file changed, 42 insertions(+), 36 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 1d85cb7..835e343 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -125,6 +125,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] = =3D }; =20 /* + * Nomenclature for variable names to simplify and clarify this code and e= ase + * any potential staring at it: + * + * @instr: source address of the original instructions in the kernel text = as + * generated by the compiler. + * + * @buf: temporary buffer on which the patching operates. This buffer is + * eventually text-poked into the kernel image. + * + * @replacement: pointer to the opcodes which are replacing @instr, locate= d in + * the .altinstr_replacement section. + */ + +/* * Fill the buffer with a single effective instruction of size @len. * * In order not to issue an ORC stack depth tracking CFI entry (Call Frame= Info) @@ -133,28 +147,28 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] = =3D * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with = INT3 and * *jump* over instead of executing long and daft NOPs. */ -static void __init_or_module add_nop(u8 *instr, unsigned int len) +static void __init_or_module add_nop(u8 *buf, unsigned int len) { - u8 *target =3D instr + len; + u8 *target =3D buf + len; =20 if (!len) return; =20 if (len <=3D ASM_NOP_MAX) { - memcpy(instr, x86_nops[len], len); + memcpy(buf, x86_nops[len], len); return; } =20 if (len < 128) { - __text_gen_insn(instr, JMP8_INSN_OPCODE, instr, target, JMP8_INSN_SIZE); - instr +=3D JMP8_INSN_SIZE; + __text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE); + buf +=3D JMP8_INSN_SIZE; } else { - __text_gen_insn(instr, JMP32_INSN_OPCODE, instr, target, JMP32_INSN_SIZE= ); - instr +=3D JMP32_INSN_SIZE; + __text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE); + buf +=3D JMP32_INSN_SIZE; } =20 - for (;instr < target; instr++) - *instr =3D INT3_INSN_OPCODE; + for (;buf < target; buf++) + *buf =3D INT3_INSN_OPCODE; } =20 extern s32 __retpoline_sites[], __retpoline_sites_end[]; @@ -187,12 +201,12 @@ static bool insn_is_nop(struct insn *insn) * Find the offset of the first non-NOP instruction starting at @offset * but no further than @len. */ -static int skip_nops(u8 *instr, int offset, int len) +static int skip_nops(u8 *buf, int offset, int len) { struct insn insn; =20 for (; offset < len; offset +=3D insn.length) { - if (insn_decode_kernel(&insn, &instr[offset])) + if (insn_decode_kernel(&insn, &buf[offset])) break; =20 if (!insn_is_nop(&insn)) @@ -207,7 +221,7 @@ static int skip_nops(u8 *instr, int offset, int len) * to the end of the NOP sequence into a single NOP. */ static bool __init_or_module -__optimize_nops(u8 *instr, size_t len, struct insn *insn, int *next, int *= prev, int *target) +__optimize_nops(const u8 * const instr, u8 *buf, size_t len, struct insn *= insn, int *next, int *prev, int *target) { int i =3D *next - insn->length; =20 @@ -222,12 +236,12 @@ __optimize_nops(u8 *instr, size_t len, struct insn *i= nsn, int *next, int *prev,=20 if (insn_is_nop(insn)) { int nop =3D i; =20 - *next =3D skip_nops(instr, *next, len); + *next =3D skip_nops(buf, *next, len); if (*target && *next =3D=3D *target) nop =3D *prev; =20 - add_nop(instr + nop, *next - nop); - DUMP_BYTES(ALT, instr, len, "%px: [%d:%d) optimized NOPs: ", instr, nop,= *next); + add_nop(buf + nop, *next - nop); + DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, *= next); return true; } =20 @@ -239,32 +253,22 @@ __optimize_nops(u8 *instr, size_t len, struct insn *i= nsn, int *next, int *prev,=20 * "noinline" to cause control flow change and thus invalidate I$ and * cause refetch after modification. */ -static void __init_or_module noinline optimize_nops(u8 *instr, size_t len) +static void __init_or_module noinline optimize_nops(const u8 * const instr= , u8 *buf, size_t len) { int prev, target =3D 0; =20 for (int next, i =3D 0; i < len; i =3D next) { struct insn insn; =20 - if (insn_decode_kernel(&insn, &instr[i])) + if (insn_decode_kernel(&insn, &buf[i])) return; =20 next =3D i + insn.length; =20 - __optimize_nops(instr, len, &insn, &next, &prev, &target); + __optimize_nops(instr, buf, len, &insn, &next, &prev, &target); } } =20 -static void __init_or_module noinline optimize_nops_inplace(u8 *instr, siz= e_t len) -{ - unsigned long flags; - - local_irq_save(flags); - optimize_nops(instr, len); - sync_core(); - local_irq_restore(flags); -} - /* * In this context, "source" is where the instructions are placed in the * section .altinstr_replacement, for example during kernel build by the @@ -336,7 +340,7 @@ bool need_reloc(unsigned long offset, u8 *src, size_t s= rc_len) } =20 static void __init_or_module noinline -apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src, size_t src_len) +apply_relocation(const u8 * const instr, u8 *buf, size_t len, u8 *src, siz= e_t src_len) { int prev, target =3D 0; =20 @@ -348,7 +352,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src= , size_t src_len) =20 next =3D i + insn.length; =20 - if (__optimize_nops(buf, len, &insn, &next, &prev, &target)) + if (__optimize_nops(instr, buf, len, &insn, &next, &prev, &target)) continue; =20 switch (insn.opcode.bytes[0]) { @@ -365,7 +369,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src= , size_t src_len) if (need_reloc(next + insn.immediate.value, src, src_len)) { apply_reloc(insn.immediate.nbytes, buf + i + insn_offset_immediate(&insn), - src - dest); + src - instr); } =20 /* @@ -373,7 +377,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src= , size_t src_len) */ if (insn.opcode.bytes[0] =3D=3D JMP32_INSN_OPCODE) { s32 imm =3D insn.immediate.value; - imm +=3D src - dest; + imm +=3D src - instr; imm +=3D JMP32_INSN_SIZE - JMP8_INSN_SIZE; if ((imm >> 31) =3D=3D (imm >> 7)) { buf[i+0] =3D JMP8_INSN_OPCODE; @@ -389,7 +393,7 @@ apply_relocation(u8 *buf, size_t len, u8 *dest, u8 *src= , size_t src_len) if (need_reloc(next + insn.displacement.value, src, src_len)) { apply_reloc(insn.displacement.nbytes, buf + i + insn_offset_displacement(&insn), - src - dest); + src - instr); } } } @@ -505,7 +509,9 @@ void __init_or_module noinline apply_alternatives(struc= t alt_instr *start, * patch if feature is *NOT* present. */ if (!boot_cpu_has(a->cpuid) =3D=3D !(a->flags & ALT_FLAG_NOT)) { - optimize_nops_inplace(instr, a->instrlen); + memcpy(insn_buff, instr, a->instrlen); + optimize_nops(instr, insn_buff, a->instrlen); + text_poke_early(instr, insn_buff, a->instrlen); continue; } =20 @@ -527,7 +533,7 @@ void __init_or_module noinline apply_alternatives(struc= t alt_instr *start, for (; insn_buff_sz < a->instrlen; insn_buff_sz++) insn_buff[insn_buff_sz] =3D 0x90; =20 - apply_relocation(insn_buff, a->instrlen, instr, replacement, a->replacem= entlen); + apply_relocation(instr, insn_buff, a->instrlen, replacement, a->replacem= entlen); =20 DUMP_BYTES(ALT, instr, a->instrlen, "%px: old_insn: ", instr); DUMP_BYTES(ALT, replacement, a->replacementlen, "%px: rpl_insn: ", rep= lacement); @@ -762,7 +768,7 @@ void __init_or_module noinline apply_retpolines(s32 *st= art, s32 *end) =20 len =3D patch_retpoline(addr, &insn, bytes); if (len =3D=3D insn.length) { - optimize_nops(bytes, len); + optimize_nops(addr, bytes, len); DUMP_BYTES(RETPOLINE, ((u8*)addr), len, "%px: orig: ", addr); DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr); text_poke_early(addr, bytes, len);