From nobody Sun Nov 24 05:57:16 2024 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 39E2F74068; Thu, 21 Nov 2024 07:39:04 +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=1732174748; cv=none; b=LNDKP58CCPMp5UNvedchr0qdsyBzYWsKBEuCRt5qm6XopFFy2b1K+jzj4cB60uqZWPb0s3zyilp0f/iME2ZDAJ+c5UlwRYZEfnkdMJSMT+cjl7/nw+YyZetdgTKDlAEfaHQ9xw0PvkToeI8Y7Ge5k6B3t1k58xdidg3CX9tQw8c= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1732174748; c=relaxed/simple; bh=0mNbvn1SFyjy2OOqBy9OO9VK2ZbbcJPMtV0ZKO8QwvY=; h=From:Date:Subject:MIME-Version:Content-Type:Message-Id:To:Cc; b=rS+Kz5NIm6ojk0BlXPsOBINt/XT7s2lXcDbYCKd+r71AymIrH1N7HQZA2HSJB/DmA1ng6Dx73CVaBNI2/jvjlgQiPe9ZydSibMGVZrZFWyY/+BYLZ3pC7cyqsiGBt7A7QhDmdvlI00NPzYjrKMnkX6gcg+gB8nGXATb+n3NtA+Y= 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=DGvKlbka; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=PxXPMGND; 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="DGvKlbka"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="PxXPMGND" From: =?utf-8?q?Thomas_Wei=C3=9Fschuh?= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1732174736; h=from:from: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; bh=Xn0nijE3Gdm1C3OOWwYkq9mZCdk+DfIymWGjrWpc1L0=; b=DGvKlbkaZESL2BDPHwxlsem3KaSSGLL/Wqi/0jZqiR2tlqiH6YdiA1/88hCfzfJtBm2fV6 SvwCEcMcHPvPP2KcXHI/SVR+/dTqPLlee7qIq4KaJ/khs63BRWe/bZ+KdukVrqUy7oYA9u ISYS3bH52yR1UKaomc+yDmi42DStMDOto2/vIygYQxatSTmz58NoaLKb4j7kf8yv9Vrr2k LDAyAOraDmaMQQG72+EfPP47QG3z7O8KhATpCR5yRtZQDD5np8vnU5TTrd7G7nLnFzOfCt jX5NyNn9HlWK/XZmAQNbJUlo10Q8QwWmpsEa5TolJa/Ne9zkz5ntVHsLRbSdbw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1732174736; h=from:from: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; bh=Xn0nijE3Gdm1C3OOWwYkq9mZCdk+DfIymWGjrWpc1L0=; b=PxXPMGNDyh4uQu0sfU5R5dn6qxE6jBGsomBOpLLWV3uYCx7TE2J1VrqIHOZPWmiETtbjfN O573Q19HLExh8wBg== Date: Thu, 21 Nov 2024 08:38:08 +0100 Subject: [PATCH] kprobes: Reduce preempt disable scope in check_kprobe_access_safe() Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20241121-kprobes-preempt-v1-1-fd581ee7fcbb@linutronix.de> X-B4-Tracking: v=1; b=H4sIAF/jPmcC/x2MWwqAIBAArxL7naBSkV0l+uix1hKVuBGBePeWP mdgJgFjJGToigQRH2K6TgFTFjBv47miokUYrLaVMVarPcRrQlYhIh7hVtq1tvE11oubQSrxnt7 /2A85f2EJ5aBhAAAA X-Change-ID: 20241120-kprobes-preempt-09826f5e5d9c To: Naveen N Rao , Anil S Keshavamurthy , "David S. Miller" , Masami Hiramatsu , Clark Williams , Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Sebastian Andrzej Siewior , linux-rt-devel@lists.linux.dev, =?utf-8?q?Thomas_Wei=C3=9Fschuh?= X-Developer-Signature: v=1; a=ed25519-sha256; t=1732174733; l=3905; i=thomas.weissschuh@linutronix.de; s=20240209; h=from:subject:message-id; bh=0mNbvn1SFyjy2OOqBy9OO9VK2ZbbcJPMtV0ZKO8QwvY=; b=0/TI3xrXhoMu8f4MLWUEecTzN5qTwekglXesD5hXPBW0zgprOOY5TJlu77HnFvZtH2feUt9nl A8DxuuU5eyFDCkU18dDNjsrowncAgxh0wFczEbILmRKiGlVruP/Qa0S X-Developer-Key: i=thomas.weissschuh@linutronix.de; a=ed25519; pk=pfvxvpFUDJV2h2nY0FidLUml22uGLSjByFbM6aqQQws= Commit a189d0350f387 ("kprobes: disable preempt for module_text_address() a= nd kernel_text_address()") introduced a preempt_disable() region to protect against concurrent module unloading. However this region also includes the call to jump_label_text_reserved() which takes a long time; up to 400us, iterating over approx 6000 jump tables. The scope protected by preempt_disable() is largen than necessary. core_kernel_text() does not need to be protected as it does not interact with module code at all. Only the scope from __module_text_address() to try_module_get() needs to be protected. By limiting the critical section to __module_text_address() and try_module_get() the function responsible for the latency spike remains preemptible. This works fine even when !CONFIG_MODULES as in that case try_module_get() will always return true and that block can be optimized away. Limit the critical section to __module_text_address() and try_module_get(). Use guard(preempt)() for easier error handling. While at it also remove a spurious *probed_mod =3D NULL in an error path. On errors the output parameter is never inspected by the caller. Some error paths were clearing the parameters, some didn't. Align them for clarity. Signed-off-by: Thomas Wei=C3=9Fschuh Reviewed-by: Sebastian Andrzej Siewior --- kernel/kprobes.c | 24 ++++++++++++------------ 1 file changed, 12 insertions(+), 12 deletions(-) diff --git a/kernel/kprobes.c b/kernel/kprobes.c index da59c68df8412c4662d39d3e286d516e8cee9a69..369020170e832a34ea9c05eda66= 93bded02ec505 100644 --- a/kernel/kprobes.c +++ b/kernel/kprobes.c @@ -39,6 +39,7 @@ #include #include #include +#include =20 #include #include @@ -1570,16 +1571,25 @@ static int check_kprobe_address_safe(struct kprobe = *p, if (ret) return ret; jump_label_lock(); - preempt_disable(); =20 /* Ensure the address is in a text area, and find a module if exists. */ *probed_mod =3D NULL; if (!core_kernel_text((unsigned long) p->addr)) { + guard(preempt)(); *probed_mod =3D __module_text_address((unsigned long) p->addr); if (!(*probed_mod)) { ret =3D -EINVAL; goto out; } + + /* + * We must hold a refcount of the probed module while updating + * its code to prohibit unexpected unloading. + */ + if (unlikely(!try_module_get(*probed_mod))) { + ret =3D -ENOENT; + goto out; + } } /* Ensure it is not in reserved area. */ if (in_gate_area_no_mm((unsigned long) p->addr) || @@ -1588,21 +1598,13 @@ static int check_kprobe_address_safe(struct kprobe = *p, static_call_text_reserved(p->addr, p->addr) || find_bug((unsigned long)p->addr) || is_cfi_preamble_symbol((unsigned long)p->addr)) { + module_put(*probed_mod); ret =3D -EINVAL; goto out; } =20 /* Get module refcount and reject __init functions for loaded modules. */ if (IS_ENABLED(CONFIG_MODULES) && *probed_mod) { - /* - * We must hold a refcount of the probed module while updating - * its code to prohibit unexpected unloading. - */ - if (unlikely(!try_module_get(*probed_mod))) { - ret =3D -ENOENT; - goto out; - } - /* * If the module freed '.init.text', we couldn't insert * kprobes in there. @@ -1610,13 +1612,11 @@ static int check_kprobe_address_safe(struct kprobe = *p, if (within_module_init((unsigned long)p->addr, *probed_mod) && !module_is_coming(*probed_mod)) { module_put(*probed_mod); - *probed_mod =3D NULL; ret =3D -ENOENT; } } =20 out: - preempt_enable(); jump_label_unlock(); =20 return ret; --- base-commit: adc218676eef25575469234709c2d87185ca223a change-id: 20241120-kprobes-preempt-09826f5e5d9c Best regards, --=20 Thomas Wei=C3=9Fschuh