From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Google-Smtp-Source: AH8x2249b+Rahbnp19Rydvqg1zkQSA0e8QaL21bUoFGyT+L0lZpQYAHr8RRweGcSYUvVZqPFLhWC ARC-Seal: i=1; a=rsa-sha256; t=1516528179; cv=none; d=google.com; s=arc-20160816; b=SvqaHRbBk0P1rumepLKoKl83rEMeWAVPXtZvdS0KUP87JMNgDdX7HDIMGRAU4qliKM gw8p+0tZ1+/jfM0HF6MV6JS/B7NIL55vJ2e8efGGiLpkaJ6U2NCQLQ0EAc1jy59IlzDC cWDDj0+zHW98eOrkwAG7hHeSxc51vLmUnw1GXJml0o9Sjq3t6kC0t9lxq+qtXku653DO sf3yMcGjnIGYk0k2eA/MYhkuZgbUAKdHL0Lm1MOjfxfQc1uLGqsiReYU0SproqNQF70/ 1428nDZaRatzdXBEr3hlimKHsddfRQgumtwidCy1MC6ru2bpO7yC+Yp6uPtBnUKRv2Oo 1aiQ== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=references:in-reply-to:message-id:date:subject:to:from :dkim-signature:arc-authentication-results; bh=061kL8zroH8l4c3tEfz/x6XYcyJCsm+f2C8rAQCOPlM=; b=PZcK9I3wI8oLXj7g+La+bI0eNS7O51J87Zngwht/KNVhV5IaLgSvHfBJzdRy4py7bQ vb7w318ZMt23olbRHAB3MkOVZ3Tv5xj6iOWTzVSqYm1EAqqJMIMHZl8ACARTHHXQJ+k6 ac2I8QvDGCdaAY30jYP9zbIRWjbq4lb0JF8A8Zmug06QcgsE9CY5HM9MQ0d3NRKKx3mk CH0ghebq8WrEMdpjcmtm29yzeLnnDbigNM0dcrIGa4vpYPdmGkQjUYwMnfxIc4x+LrsT +3vhv1jo3Yp6KtnixpH2m2J+IuZKZ2TrX5YApjvegZwSfX8ExQucrwsaWUnSM7b20ua0 7FxA== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=JIgDQsF7; spf=pass (google.com: domain of prvs=552b621e3=dwmw@amazon.com designates 72.21.198.25 as permitted sender) smtp.mailfrom=prvs=552b621e3=dwmw@amazon.com; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk Authentication-Results: mx.google.com; dkim=pass header.i=@amazon.co.uk header.s=amazon201209 header.b=JIgDQsF7; spf=pass (google.com: domain of prvs=552b621e3=dwmw@amazon.com designates 72.21.198.25 as permitted sender) smtp.mailfrom=prvs=552b621e3=dwmw@amazon.com; dmarc=pass (p=QUARANTINE sp=QUARANTINE dis=NONE) header.from=amazon.co.uk X-IronPort-AV: E=Sophos;i="5.46,390,1511827200"; d="scan'208";a="704575208" From: David Woodhouse To: arjan@linux.intel.com, tglx@linutronix.de, karahmed@amazon.de, x86@kernel.org, linux-kernel@vger.kernel.org, tim.c.chen@linux.intel.com, bp@alien8.de, peterz@infradead.org, pbonzini@redhat.com, ak@linux.intel.com, torvalds@linux-foundation.org, gregkh@linux-foundation.org Subject: [PATCH v2 8/8] x86/mm: Only flush indirect branches when switching into non dumpable process Date: Sun, 21 Jan 2018 09:49:09 +0000 Message-Id: <1516528149-9370-9-git-send-email-dwmw@amazon.co.uk> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1516528149-9370-1-git-send-email-dwmw@amazon.co.uk> References: <1516528149-9370-1-git-send-email-dwmw@amazon.co.uk> X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: =?utf-8?q?1590195052643423989?= X-GMAIL-MSGID: =?utf-8?q?1590195052643423989?= X-Mailing-List: linux-kernel@vger.kernel.org List-ID: From: Andi Kleen Flush indirect branches when switching into a process that marked itself non dumpable. This protects high value processes like gpg better, without having too high performance overhead. Signed-off-by: Andi Kleen Signed-off-by: David Woodhouse Signed-off-by: KarimAllah Ahmed --- arch/x86/mm/tlb.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-) diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c index 304de7d..f64e80c 100644 --- a/arch/x86/mm/tlb.c +++ b/arch/x86/mm/tlb.c @@ -225,8 +225,19 @@ void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next, * Avoid user/user BTB poisoning by flushing the branch predictor * when switching between processes. This stops one process from * doing Spectre-v2 attacks on another. + * + * As an optimization: Flush indirect branches only when + * switching into processes that disable dumping. + * + * This will not flush when switching into kernel threads. + * But it would flush when switching into idle and back + * + * It might be useful to have a one-off cache here + * to also not flush the idle case, but we would need some + * kind of stable sequence number to remember the previous mm. */ - indirect_branch_prediction_barrier(); + if (tsk && tsk->mm && get_dumpable(tsk->mm) != SUID_DUMP_USER) + indirect_branch_prediction_barrier(); if (IS_ENABLED(CONFIG_VMAP_STACK)) { /* -- 2.7.4