From nobody Sat Feb 7 15:10:58 2026 Received: from mgamail.intel.com (mgamail.intel.com [192.198.163.9]) (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 63F4815F3E2; Mon, 25 Mar 2024 06:41:26 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=192.198.163.9 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711348888; cv=none; b=p0yL1ZHw9sxfAeOSn/hjVJi2IXh5Z9iBOpaqS1j4uL9uECJzpi4Om2/hgHZ/zww/FsvvkUBsR2NobdAfZ26kPcGqY4wUEu56iuY5xMDr5NdDH6KnxaeKWrX0sfI7HIbov7wzwH2dtv0QZo9ChzuOyTCco5bWxnweGgYoesJx/eI= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1711348888; c=relaxed/simple; bh=Zjh6IUndlImHk90vhCoelXOI1d7rMagiowI5tzl77NQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=nI59wntMQwHShCXljF/y9H0PtnTBJo93RYSVIWo3D0vOuGK3lw6CYgLX5ZzfS56dT668gVPb50GxzjmwRtQBPUb6PGbhvBLLKfLi38DvPjj12J0GI1M5jiEg5bNcOnkBP83RbrvxZEl4UOfxQoR7UYY614AR3auXtOcBhyn8Zbs= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com; spf=pass smtp.mailfrom=intel.com; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b=d2HRW4RJ; arc=none smtp.client-ip=192.198.163.9 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=intel.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=intel.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=intel.com header.i=@intel.com header.b="d2HRW4RJ" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1711348886; x=1742884886; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=Zjh6IUndlImHk90vhCoelXOI1d7rMagiowI5tzl77NQ=; b=d2HRW4RJ+Whp0NALxuEas08Z+GpG7vgYUH0VRQzlWPQq9HbPC0k4bN6A 0kJcy6Jrvhn6cwVCPLaxIXxitFfkdcTSGbuevtu5QcKHIf9vCYufhnOSg +WJfdRqxOvbZM+VQIH1qoPxQzAQYztrotZ6aNvMminNzuemJMlT4ooJRK 1SnsQYtfqCzqgK6lKnpi2xVmwcLwthVJCLa/Qrf7YHkcvb5WKKDjJoeKx de9gHSzCdP2tSAs+GTPWMhdfVH35Jx5hJfjPFatMx42I8rWTJ7XqfqRzY tbpRag46J17Gym4ftdr1IpxzraYdehNh664IVNnFiMBwzsHUVgiAMQVi5 g==; X-IronPort-AV: E=McAfee;i="6600,9927,11023"; a="17065197" X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="17065197" Received: from fmviesa002.fm.intel.com ([10.60.135.142]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2024 23:41:24 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.07,152,1708416000"; d="scan'208";a="38629597" Received: from ahunter6-mobl1.ger.corp.intel.com (HELO ahunter-VirtualBox.home\044ger.corp.intel.com) ([10.251.211.155]) by fmviesa002-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Mar 2024 23:41:18 -0700 From: Adrian Hunter To: Thomas Gleixner Cc: Michael Ellerman , Nicholas Piggin , Christophe Leroy , "Aneesh Kumar K.V" , "Naveen N. Rao" , Heiko Carstens , Vasily Gorbik , Alexander Gordeev , Christian Borntraeger , Sven Schnelle , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andy Lutomirski , Vincenzo Frascino , John Stultz , Stephen Boyd , Peter Zijlstra , Randy Dunlap , Bjorn Helgaas , Arnd Bergmann , Anna-Maria Behnsen , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org Subject: [PATCH V2 07/19] vdso: Make delta calculation overflow safe Date: Mon, 25 Mar 2024 08:40:11 +0200 Message-Id: <20240325064023.2997-8-adrian.hunter@intel.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20240325064023.2997-1-adrian.hunter@intel.com> References: <20240325064023.2997-1-adrian.hunter@intel.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Kernel timekeeping is designed to keep the change in cycles (since the last timer interrupt) below max_cycles, which prevents multiplication overflow when converting cycles to nanoseconds. However, if timer interrupts stop, the calculation will eventually overflow. Add protection against that, enabled by config option CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT. Check against max_cycles, falling back to a slower higher precision calculation. Suggested-by: Thomas Gleixner Signed-off-by: Adrian Hunter --- lib/vdso/gettimeofday.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-) diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c index 9fa90e0794c9..9c3a8d2440c9 100644 --- a/lib/vdso/gettimeofday.c +++ b/lib/vdso/gettimeofday.c @@ -13,6 +13,18 @@ # define VDSO_DELTA_MASK(vd) (vd->mask) #endif =20 +#ifdef CONFIG_GENERIC_VDSO_OVERFLOW_PROTECT +static __always_inline bool vdso_delta_ok(const struct vdso_data *vd, u64 = delta) +{ + return delta < vd->max_cycles; +} +#else +static __always_inline bool vdso_delta_ok(const struct vdso_data *vd, u64 = delta) +{ + return true; +} +#endif + #ifndef vdso_shift_ns static __always_inline u64 vdso_shift_ns(u64 ns, u32 shift) { @@ -28,7 +40,10 @@ static __always_inline u64 vdso_calc_ns(const struct vds= o_data *vd, u64 cycles, { u64 delta =3D (cycles - vd->cycle_last) & VDSO_DELTA_MASK(vd); =20 - return vdso_shift_ns((delta * vd->mult) + base, vd->shift); + if (likely(vdso_delta_ok(vd, delta))) + return vdso_shift_ns((delta * vd->mult) + base, vd->shift); + + return mul_u64_u32_add_u64_shr(delta, vd->mult, base, vd->shift); } #endif /* vdso_calc_ns */ =20 --=20 2.34.1