linux-kernel - [PATCH] arm64: cpufeature: make sure cpu_mitigations

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Message-Id: <1655382938-126283-1-git-send-email-liusong@linux.alibaba.com>
Date:   Thu, 16 Jun 2022 20:35:38 +0800
From:   Liu Song <liusong@...ux.alibaba.com>
To:     catalin.marinas@....com, will@...nel.org
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] arm64: cpufeature: make sure cpu_mitigations_off then kpti off

From: Liu Song <liusong@...ux.alibaba.com>

If kaslr is enabled, kpti cannot be turned off even if "mitigations=off",
adjust the code order to ensure that kpti is off when "mitigations=off".

Signed-off-by: Liu Song <liusong@...ux.alibaba.com>
---
 arch/arm64/kernel/cpufeature.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index 42ea2bd..27d4850 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -1616,6 +1616,11 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 		__kpti_forced = -1;
 	}
 
+	if (cpu_mitigations_off() && !__kpti_forced) {
+		str = "mitigations=off";
+		__kpti_forced = -1;
+	}
+
 	/* Useful for KASLR robustness */
 	if (kaslr_requires_kpti()) {
 		if (!__kpti_forced) {
@@ -1624,11 +1629,6 @@ static bool unmap_kernel_at_el0(const struct arm64_cpu_capabilities *entry,
 		}
 	}
 
-	if (cpu_mitigations_off() && !__kpti_forced) {
-		str = "mitigations=off";
-		__kpti_forced = -1;
-	}
-
 	if (!IS_ENABLED(CONFIG_UNMAP_KERNEL_AT_EL0)) {
 		pr_info_once("kernel page table isolation disabled by kernel configuration\n");
 		return false;
-- 
1.8.3.1