linux-kernel - [PATCH] x86/speculation: Check whether speculation is force disabled

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Date:   Wed, 3 Jun 2020 07:12:35 +0000
From:   "Tada, Kenta (Sony)" <Kenta.Tada@...y.com>
To:     "x86@...nel.org" <x86@...nel.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "jpoimboe@...hat.com" <jpoimboe@...hat.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "longman@...hat.com" <longman@...hat.com>,
        "pawan.kumar.gupta@...ux.intel.com" 
        <pawan.kumar.gupta@...ux.intel.com>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: [PATCH] x86/speculation: Check whether speculation is force disabled

Once PR_SPEC_FORCE_DISABLE is set, users cannot set PR_SPEC_ENABLE.
This commit checks whether PR_SPEC_FORCE_DISABLE was previously set.

Signed-off-by: Kenta Tada <Kenta.Tada@...y.com>
---
 arch/x86/kernel/cpu/bugs.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index ed54b3b21c39..678ace157035 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -1173,6 +1173,9 @@ static int ib_prctl_set(struct task_struct *task, unsigned long ctrl)
 		if (spectre_v2_user == SPECTRE_V2_USER_STRICT ||
 		    spectre_v2_user == SPECTRE_V2_USER_STRICT_PREFERRED)
 			return -EPERM;
+		/* If speculation is force disabled, enable is not allowed */
+		if (task_spec_ib_force_disable(task))
+			return -EPERM;
 		task_clear_spec_ib_disable(task);
 		task_update_spec_tif(task);
 		break;
-- 
2.20.1