From nobody Wed Dec 24 01:49:45 2025 Received: from mail.alien8.de (mail.alien8.de [65.109.113.108]) (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 DDD2766B5E for ; Tue, 30 Jan 2024 11:00:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=65.109.113.108 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706612404; cv=none; b=eRSyzhNK0SRUqeGCjJK2P/gK0Mo7ZiZ2KztTKAtcGMNcRr/1MvUdX2ZMLSXxG5hMfmOV+FsegtZ4qeZaEUrY3z7C4QHQZpHKDxJKeXHgx/evO+1gCg8bfnkbEOhp+/Z3/Uqp6NycS0qclZHbC0zaYBtAFSarU8lIir3fh+Evulg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1706612404; c=relaxed/simple; bh=S6v5NG3zkWzybZS+L6ZCuQTTnUlx2jbdtvaXdKu2GAw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UNxEYpxy0RTX+RMshQSbTazZIw9Hyx7OF0l4dUbOLp3OjTckIDjGg3u+J2baanKQQTtzvG1Q/rYc1JyDyPYSzHu2vcnJYC84fDCyvVN5WxlVDXTqiOQS4A6O05Xw3GdUs6qobuEGPw7J6PKhKcvQ74OWDIsS4rIAntb+lXaM0tA= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de; spf=pass smtp.mailfrom=alien8.de; dkim=fail (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b=NtM6XUdy reason="signature verification failed"; arc=none smtp.client-ip=65.109.113.108 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=alien8.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=alien8.de Authentication-Results: smtp.subspace.kernel.org; dkim=fail reason="signature verification failed" (4096-bit key) header.d=alien8.de header.i=@alien8.de header.b="NtM6XUdy" Received: from localhost (localhost.localdomain [127.0.0.1]) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTP id E168B40E01BB; Tue, 30 Jan 2024 10:59:59 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at mail.alien8.de Authentication-Results: mail.alien8.de (amavisd-new); dkim=fail (4096-bit key) reason="fail (body has been altered)" header.d=alien8.de Received: from mail.alien8.de ([127.0.0.1]) by localhost (mail.alien8.de [127.0.0.1]) (amavisd-new, port 10026) with ESMTP id Zr7zz19iKXhN; Tue, 30 Jan 2024 10:59:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=alien8; t=1706612397; bh=Nzb7MQEnsKeU91bcnGcqQoyDmQJKUpafnfMpQ9uplZ8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=NtM6XUdyOGaMTSux6J2dRXVlZM6So+Ty9wR4Cxs3uMIsJ41WIrgJ6mXk05DiWCOIy sU9uu7SjzzkQjQJBj9Vh2jod9hREa+F5/oeShrHg3Hf/0E8ijkx1i1Ywuhrx7hW8Bg FwqGzixLJ5lDtcyA1UaZOMM6chzyCuahkBa+ASOgTZhSL82W5IWGH/FJ68YteybMo+ I2TBm2KnRp7yAzuPQGo2lRg11jc9NgawaeoLe+ogd+BqVlxEHU439Pqdx/dEl7lIwi YSarGScGDRAgnDX7kYZtHkHLL5Qmh/8GFESOfyHN4TbpCPJ4c6atvbh7vC9JMf+Wnr alwGLPA2cHXtJqLxzHC8t83hkfuEp01IWY8V3Sf+iYOI84nN0OmCVSnxru5g1MmH5d s4OGbs1dfyU2oTrqBcEpQFPi8ikviXEbb2xEMiLxl6iDlVElGgPqF+zZEXCRp7flvV if4hkmHeO9KQHd+j1MZZLSg9tvfcQBIbTkYQWaKyedPCq/3rp9Lx6aCIKuHQSe3LT/ vFkUQ7yu0RPwVS3gPyr5UlTIGdkjPXwX5OtFWAndSJ5xZ0YDf1LCERff0rb/RAuuJO ZDL6iHvI1pF+h7mPgRiM1UCRr3lspm6CwDXlrK5sqTYAVdZ2RVKo/zq4gs1FHA1SLu LP/fvJzkcfQKv6YRjo8lCy0Y= Received: from zn.tnic (pd953033e.dip0.t-ipconnect.de [217.83.3.62]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature ECDSA (P-256) server-digest SHA256) (No client certificate requested) by mail.alien8.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 331CC40E0177; Tue, 30 Jan 2024 10:59:53 +0000 (UTC) From: Borislav Petkov To: X86 ML Cc: Paul Gortmaker , LKML , Thomas Gleixner Subject: [PATCH 1/4] x86/alternatives: Use a temporary buffer when optimizing NOPs Date: Tue, 30 Jan 2024 11:59:38 +0100 Message-ID: <20240130105941.19707-2-bp@alien8.de> X-Mailer: git-send-email 2.43.0 In-Reply-To: <20240130105941.19707-1-bp@alien8.de> References: <20240130105941.19707-1-bp@alien8.de> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: "Borislav Petkov (AMD)" Instead of optimizing NOPs inplace, 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 --- 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 cc130b57542a..d633eb59f2b6 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -124,6 +124,20 @@ const unsigned char * const x86_nops[ASM_NOP_MAX+1] = =3D #endif }; =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. * @@ -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, 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, * "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); --=20 2.43.0