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 BC6C827875C; Wed, 17 Sep 2025 16:04:23 +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=1758125063; cv=none; b=Z6PqkjgG718S8A65pQJTcP3BjZC5vs7pXFvyzI883k/e7/zZd+kV2DwRGwrA1Is9mn2yKVgzcerXBV/+2WvKxqpcQ3lly6lwKDNLfUUZFGuzbtNguFZjir3MDElZ3DPYpY5e3DGDpBqyagHXL/w85Yr0L3H1SP4JHQyyiInHzyM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758125063; c=relaxed/simple; bh=eHw0u6kn/e6VWlDUX7+51egTO7nADQPtQ5LmQ4ML06Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=UDgy5GKkDo9ujGFl5EA24bJDazLW3Mp1DEUR6k4Tmx22GLDOfgYLkkiDmHFIHW9xRBDWOvR86kqMngOkrr+SUMG7/ANKyakEUh7/iVoD0Q1tLxGICysDzr6FNX45mk6K/M/JU+s0lJ6gzrQTaZFI/AOAuf5YNPxcXiGI0oKeECg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OM1pFhw8; 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="OM1pFhw8" Received: by smtp.kernel.org (Postfix) with ESMTPSA id C572BC19421; Wed, 17 Sep 2025 16:04:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758125063; bh=eHw0u6kn/e6VWlDUX7+51egTO7nADQPtQ5LmQ4ML06Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=OM1pFhw8q6gShh4qAiGYO5IYrvhr80DkYXOapti0woV45TFRpxV8s84DfGw3tnRCW e9zhOF7ttNdRowHlwd9OI7mx88NYODXbPrkgBtzR/8D9OaBJWpkk/1EzBULNZNUqlJ KmwG7V7+jhQKuswk++eStTK8uoobDUSO17NT8haat2d8UF/GGQrfWCdmY3n1mIIPIX 6LTateE28PYDre7gM6fUvz0zGvctqfgj+MHmOW9uExI30zdjSb4uApd4FJz5j/m5+c w7vHXFFsS7nuaYSx/k5+gVcUv4pOscD6I/GrmFgKM6PVF80aFJqCquPQdQTva6iBH9 dGafaZCRQuDQw== From: Josh Poimboeuf To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Petr Mladek , Miroslav Benes , Joe Lawrence , live-patching@vger.kernel.org, Song Liu , laokz , Jiri Kosina , Marcos Paulo de Souza , Weinan Liu , Fazla Mehrab , Chen Zhongjin , Puranjay Mohan , Dylan Hatch , Peter Zijlstra Subject: [PATCH v4 10/63] x86/alternative: Refactor INT3 call emulation selftest Date: Wed, 17 Sep 2025 09:03:18 -0700 Message-ID: <5568a50fd9cb11435e18c05a9841cd88a4d664ac.1758067942.git.jpoimboe@kernel.org> X-Mailer: git-send-email 2.50.0 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit The INT3 call emulation selftest is a bit fragile as it relies on the compiler not inserting any extra instructions before the int3_selftest_ip() definition. Also, the int3_selftest_ip() symbol overlaps with the int3_selftest symbol(), which can confuse objtool. Fix those issues by slightly reworking the functionality and moving int3_selftest_ip() to a separate asm function. While at it, improve the naming. Signed-off-by: Josh Poimboeuf --- arch/x86/kernel/alternative.c | 51 +++++++++++++++++++---------------- 1 file changed, 28 insertions(+), 23 deletions(-) diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c index 69fb818df2eed..9e7f03172a227 100644 --- a/arch/x86/kernel/alternative.c +++ b/arch/x86/kernel/alternative.c @@ -2244,21 +2244,34 @@ int alternatives_text_reserved(void *start, void *end) * See entry_{32,64}.S for more details. */ -/* - * We define the int3_magic() function in assembly to control the calling - * convention such that we can 'call' it from assembly. - */ - -extern void int3_magic(unsigned int *ptr); /* defined in asm */ +extern void int3_selftest_asm(unsigned int *ptr); asm ( " .pushsection .init.text, \"ax\", @progbits\n" -" .type int3_magic, @function\n" -"int3_magic:\n" +" .type int3_selftest_asm, @function\n" +"int3_selftest_asm:\n" ANNOTATE_NOENDBR -" movl $1, (%" _ASM_ARG1 ")\n" + /* + * INT3 padded with NOP to CALL_INSN_SIZE. The INT3 triggers an + * exception, then the int3_exception_nb notifier emulates a call to + * int3_selftest_callee(). + */ +" int3; nop; nop; nop; nop\n" ASM_RET -" .size int3_magic, .-int3_magic\n" +" .size int3_selftest_asm, . - int3_selftest_asm\n" +" .popsection\n" +); + +extern void int3_selftest_callee(unsigned int *ptr); + +asm ( +" .pushsection .init.text, \"ax\", @progbits\n" +" .type int3_selftest_callee, @function\n" +"int3_selftest_callee:\n" + ANNOTATE_NOENDBR +" movl $0x1234, (%" _ASM_ARG1 ")\n" + ASM_RET +" .size int3_selftest_callee, . - int3_selftest_callee\n" " .popsection\n" ); @@ -2267,7 +2280,7 @@ extern void int3_selftest_ip(void); /* defined in asm below */ static int __init int3_exception_notify(struct notifier_block *self, unsigned long val, void *data) { - unsigned long selftest = (unsigned long)&int3_selftest_ip; + unsigned long selftest = (unsigned long)&int3_selftest_asm; struct die_args *args = data; struct pt_regs *regs = args->regs; @@ -2282,7 +2295,7 @@ int3_exception_notify(struct notifier_block *self, unsigned long val, void *data if (regs->ip - INT3_INSN_SIZE != selftest) return NOTIFY_DONE; - int3_emulate_call(regs, (unsigned long)&int3_magic); + int3_emulate_call(regs, (unsigned long)&int3_selftest_callee); return NOTIFY_STOP; } @@ -2298,19 +2311,11 @@ static noinline void __init int3_selftest(void) BUG_ON(register_die_notifier(&int3_exception_nb)); /* - * Basically: int3_magic(&val); but really complicated :-) - * - * INT3 padded with NOP to CALL_INSN_SIZE. The int3_exception_nb - * notifier above will emulate CALL for us. + * Basically: int3_selftest_callee(&val); but really complicated :-) */ - asm volatile ("int3_selftest_ip:\n\t" - ANNOTATE_NOENDBR - " int3; nop; nop; nop; nop\n\t" - : ASM_CALL_CONSTRAINT - : __ASM_SEL_RAW(a, D) (&val) - : "memory"); + int3_selftest_asm(&val); - BUG_ON(val != 1); + BUG_ON(val != 0x1234); unregister_die_notifier(&int3_exception_nb); } -- 2.50.0