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 53D4F2EF67E; Tue, 15 Jul 2025 13:57:13 +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=1752587833; cv=none; b=ttJsCE8DbaIv63VBCvUdjsXyGmmDACnSIFDL3683leg8o/rcxt1XLLazj6qBodj6OyJe6iOrAld3MxiAkVE0yy/UyhZ+4KeD/y1f9K9yxlTd9DWhrsYm47L+TUj1QFHChTYHgXkV3ugbDN5gQ+TX1294KIWhsvwCVmlj3LifuLI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1752587833; c=relaxed/simple; bh=cM7ACrnFCPBYAlW/ZEuZ15EbcHOL4lG2qFXb/xEXXCE=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qRyf+Pd/E4R996yIxFAQIgKFJJlqDXEXgRxjW1poJTmj4N00i06Y2ly4pGCl7bF/6CKOLxO3Y8R7TjwSBmeA8i+pJYhC+GNRLCimrvXScWinq8FmJRyweOaz7VUj07dfitWbnvfy9R4VKwx1Tfo7oMgiBYS2m2/uehuAn7uEon0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=0hfBU8am; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="0hfBU8am" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DAE92C4CEF1; Tue, 15 Jul 2025 13:57:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1752587833; bh=cM7ACrnFCPBYAlW/ZEuZ15EbcHOL4lG2qFXb/xEXXCE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=0hfBU8amATjlB+ORD8tyLUHBFlTCd889HVy/wjgX9pkK4RmwKpZEi7iGeUjzm33Fe bo8rJU/nr1Fmv5mdS8qJH+u//I+8mYB4SSFyES8LlJdv8iD68NGAuG5zJ540EOQ3C5 S+Gn1/G2Fi5vZC426NyU1oCsONNnkjDprqRFJB9k= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, "Peter Zijlstra (Intel)" , Ingo Molnar , "Masami Hiramatsu (Google)" , Thadeu Lima de Souza Cascardo , Pawan Gupta Subject: [PATCH 5.10 159/208] x86/alternatives: Teach text_poke_bp() to patch Jcc.d32 instructions Date: Tue, 15 Jul 2025 15:14:28 +0200 Message-ID: <20250715130817.352516742@linuxfoundation.org> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20250715130810.830580412@linuxfoundation.org> References: <20250715130810.830580412@linuxfoundation.org> User-Agent: quilt/0.68 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra commit ac0ee0a9560c97fa5fe1409e450c2425d4ebd17a upstream. In order to re-write Jcc.d32 instructions text_poke_bp() needs to be taught about them. The biggest hurdle is that the whole machinery is currently made for 5 byte instructions and extending this would grow struct text_poke_loc which is currently a nice 16 bytes and used in an array. However, since text_poke_loc contains a full copy of the (s32) displacement, it is possible to map the Jcc.d32 2 byte opcodes to Jcc.d8 1 byte opcode for the int3 emulation. This then leaves the replacement bytes; fudge that by only storing the last 5 bytes and adding the rule that 'length == 6' instruction will be prefixed with a 0x0f byte. Change-Id: Ie3f72c6b92f865d287c8940e5a87e59d41cfaa27 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Link: https://lore.kernel.org/r/20230123210607.115718513@infradead.org [cascardo: there is no emit_call_track_retpoline] Signed-off-by: Thadeu Lima de Souza Cascardo Signed-off-by: Pawan Gupta Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/alternative.c | 56 +++++++++++++++++++++++++++++++++++------- 1 file changed, 47 insertions(+), 9 deletions(-) --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -506,6 +506,12 @@ next: kasan_enable_current(); } +static inline bool is_jcc32(struct insn *insn) +{ + /* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */ + return insn->opcode.bytes[0] == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80; +} + #if defined(CONFIG_RETPOLINE) && defined(CONFIG_STACK_VALIDATION) /* @@ -1331,6 +1337,11 @@ void text_poke_sync(void) on_each_cpu(do_sync_core, NULL, 1); } +/* + * NOTE: crazy scheme to allow patching Jcc.d32 but not increase the size of + * this thing. When len == 6 everything is prefixed with 0x0f and we map + * opcode to Jcc.d8, using len to distinguish. + */ struct text_poke_loc { /* addr := _stext + rel_addr */ s32 rel_addr; @@ -1452,6 +1463,10 @@ noinstr int poke_int3_handler(struct pt_ int3_emulate_jmp(regs, (long)ip + tp->disp); break; + case 0x70 ... 0x7f: /* Jcc */ + int3_emulate_jcc(regs, tp->opcode & 0xf, (long)ip, tp->disp); + break; + default: BUG(); } @@ -1525,16 +1540,26 @@ static void text_poke_bp_batch(struct te * Second step: update all but the first byte of the patched range. */ for (do_sync = 0, i = 0; i < nr_entries; i++) { - u8 old[POKE_MAX_OPCODE_SIZE] = { tp[i].old, }; + u8 old[POKE_MAX_OPCODE_SIZE+1] = { tp[i].old, }; + u8 _new[POKE_MAX_OPCODE_SIZE+1]; + const u8 *new = tp[i].text; int len = tp[i].len; if (len - INT3_INSN_SIZE > 0) { memcpy(old + INT3_INSN_SIZE, text_poke_addr(&tp[i]) + INT3_INSN_SIZE, len - INT3_INSN_SIZE); + + if (len == 6) { + _new[0] = 0x0f; + memcpy(_new + 1, new, 5); + new = _new; + } + text_poke(text_poke_addr(&tp[i]) + INT3_INSN_SIZE, - (const char *)tp[i].text + INT3_INSN_SIZE, + new + INT3_INSN_SIZE, len - INT3_INSN_SIZE); + do_sync++; } @@ -1562,8 +1587,7 @@ static void text_poke_bp_batch(struct te * The old instruction is recorded so that the event can be * processed forwards or backwards. */ - perf_event_text_poke(text_poke_addr(&tp[i]), old, len, - tp[i].text, len); + perf_event_text_poke(text_poke_addr(&tp[i]), old, len, new, len); } if (do_sync) { @@ -1580,10 +1604,15 @@ static void text_poke_bp_batch(struct te * replacing opcode. */ for (do_sync = 0, i = 0; i < nr_entries; i++) { - if (tp[i].text[0] == INT3_INSN_OPCODE) + u8 byte = tp[i].text[0]; + + if (tp[i].len == 6) + byte = 0x0f; + + if (byte == INT3_INSN_OPCODE) continue; - text_poke(text_poke_addr(&tp[i]), tp[i].text, INT3_INSN_SIZE); + text_poke(text_poke_addr(&tp[i]), &byte, INT3_INSN_SIZE); do_sync++; } @@ -1601,9 +1630,11 @@ static void text_poke_loc_init(struct te const void *opcode, size_t len, const void *emulate) { struct insn insn; - int ret, i; + int ret, i = 0; - memcpy((void *)tp->text, opcode, len); + if (len == 6) + i = 1; + memcpy((void *)tp->text, opcode+i, len-i); if (!emulate) emulate = opcode; @@ -1614,6 +1645,13 @@ static void text_poke_loc_init(struct te tp->len = len; tp->opcode = insn.opcode.bytes[0]; + if (is_jcc32(&insn)) { + /* + * Map Jcc.d32 onto Jcc.d8 and use len to distinguish. + */ + tp->opcode = insn.opcode.bytes[1] - 0x10; + } + switch (tp->opcode) { case RET_INSN_OPCODE: case JMP32_INSN_OPCODE: @@ -1630,7 +1668,6 @@ static void text_poke_loc_init(struct te BUG_ON(len != insn.length); }; - switch (tp->opcode) { case INT3_INSN_OPCODE: case RET_INSN_OPCODE: @@ -1639,6 +1676,7 @@ static void text_poke_loc_init(struct te case CALL_INSN_OPCODE: case JMP32_INSN_OPCODE: case JMP8_INSN_OPCODE: + case 0x70 ... 0x7f: /* Jcc */ tp->disp = insn.immediate.value; break;