From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62023C4743C for ; Wed, 23 Jun 2021 12:25:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4C5606108E for ; Wed, 23 Jun 2021 12:25:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230157AbhFWM2D (ORCPT ); Wed, 23 Jun 2021 08:28:03 -0400 Received: from Galois.linutronix.de ([193.142.43.55]:36710 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231320AbhFWM0z (ORCPT ); Wed, 23 Jun 2021 08:26:55 -0400 Message-Id: <20210623121456.399107624@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1624451077; 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: references:references; bh=/ymlPjCvQ6fAwzLlz/UnrN3GToe0ytIgsbF9h2BnLOo=; b=zwhzWWDjL8uU/xiCh338cgSxhUOtJTHkdkvR1broA0/9/7NL4a7+dCwwa6X+fJ+TSAYkoL lymS06HTsAx+fNMmLmj9DoJKCwJpw1vpyGv2O3H1jRzeYetkKKQALo92fRJOolAxLjwoy/ x5ap35Qq3RugUAuy7ufhtV34M8Xp2lbp6l6EF/aJPUoVnF7MwXiBQvc3s4tu9Tn4m/yqXo OQv8qYwljOo+9Uj8Tu1Kv/SGc7iA9giyxdfYw3tX8cApfejVxow75ygYxeAP30Xqt07QP2 2myhS9/i4pSsJ0kY+8OkO2kyVEvytSHUv47T0PKWZgZFpw5i1absWdalhJmmsw== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1624451077; 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: references:references; bh=/ymlPjCvQ6fAwzLlz/UnrN3GToe0ytIgsbF9h2BnLOo=; b=0z6ermdlGwD3OAvi0b0tYlt6g8VBTgb/hFZzK7QCFsN+1AdCWjO4Qur3D2ijNUauBKiZ+Y jCEOQ7HDQ4ZyzVCg== Date: Wed, 23 Jun 2021 14:02:18 +0200 From: Thomas Gleixner To: LKML Cc: Andy Lutomirski , Dave Hansen , Fenghua Yu , Tony Luck , Yu-cheng Yu , Sebastian Andrzej Siewior , Borislav Petkov , Peter Zijlstra , Kan Liang , "Chang Seok Bae" , Megha Dey , Oliver Sang Subject: [patch V4 51/65] x86/fpu: Add PKRU storage outside of task XSAVE buffer References: <20210623120127.327154589@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-transfer-encoding: 8-bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Dave Hansen PKRU is currently partly XSAVE-managed and partly not. It has space in the task XSAVE buffer and is context-switched by XSAVE/XRSTOR. However, it is switched more eagerly than FPU because there may be a need for PKRU to be up-to-date for things like copy_to/from_user() since PKRU affects user-permission memory accesses, not just accesses from userspace itself. This leaves PKRU in a very odd position. XSAVE brings very little value to the table for how Linux uses PKRU except for signal related XSTATE handling. Prepare to move PKRU away from being XSAVE-managed. Allocate space in the thread_struct for it and save/restore it in the context-switch path separately from the XSAVE-managed features. task->thread_struct.pkru is only valid when the task is scheduled out. For the current task the authoritative source is the hardware, i.e. it has to be retrieved via rdpkru(). Leave the XSAVE code in place for now to ensure bisectability. Signed-off-by: Dave Hansen Signed-off-by: Thomas Gleixner Reviewed-by: Borislav Petkov --- V3: Fix the fallout on !PKRU enabled systems in copy_thread() - Intel testing via Dave --- arch/x86/include/asm/processor.h | 9 +++++++++ arch/x86/kernel/process.c | 7 +++++++ arch/x86/kernel/process_64.c | 25 +++++++++++++++++++++++++ 3 files changed, 41 insertions(+) --- a/arch/x86/include/asm/processor.h +++ b/arch/x86/include/asm/processor.h @@ -518,6 +518,15 @@ struct thread_struct { unsigned int sig_on_uaccess_err:1; + /* + * Protection Keys Register for Userspace. Loaded immediately on + * context switch. Store it in thread_struct to avoid a lookup in + * the tasks's FPU xstate buffer. This value is only valid when a + * task is scheduled out. For 'current' the authoritative source of + * PKRU is the hardware itself. + */ + u32 pkru; + /* Floating point and extended processor state */ struct fpu fpu; /* --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -156,11 +156,18 @@ int copy_thread(unsigned long clone_flag /* Kernel thread ? */ if (unlikely(p->flags & PF_KTHREAD)) { + p->thread.pkru = pkru_get_init_value(); memset(childregs, 0, sizeof(struct pt_regs)); kthread_frame_init(frame, sp, arg); return 0; } + /* + * Clone current's PKRU value from hardware. tsk->thread.pkru + * is only valid when scheduled out. + */ + p->thread.pkru = read_pkru(); + frame->bx = 0; *childregs = *current_pt_regs(); childregs->ax = 0; --- a/arch/x86/kernel/process_64.c +++ b/arch/x86/kernel/process_64.c @@ -340,6 +340,29 @@ static __always_inline void load_seg_leg } } +/* + * Store prev's PKRU value and load next's PKRU value if they differ. PKRU + * is not XSTATE managed on context switch because that would require a + * lookup in the task's FPU xsave buffer and require to keep that updated + * in various places. + */ +static __always_inline void x86_pkru_load(struct thread_struct *prev, + struct thread_struct *next) +{ + if (!cpu_feature_enabled(X86_FEATURE_OSPKE)) + return; + + /* Stash the prev task's value: */ + prev->pkru = rdpkru(); + + /* + * PKRU writes are slightly expensive. Avoid them when not + * strictly necessary: + */ + if (prev->pkru != next->pkru) + wrpkru(next->pkru); +} + static __always_inline void x86_fsgsbase_load(struct thread_struct *prev, struct thread_struct *next) { @@ -589,6 +612,8 @@ void compat_start_thread(struct pt_regs x86_fsgsbase_load(prev, next); + x86_pkru_load(prev, next); + /* * Switch the PDA and FPU contexts. */