linux-kernel - [tip: x86/urgent] x86/cpu: Actually turn off mitigations by default for SPECULATION

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Date: Wed, 10 Apr 2024 14:31:19 -0000
From: "tip-bot2 for Sean Christopherson" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Sean Christopherson <seanjc@...gle.com>, Ingo Molnar <mingo@...nel.org>,
 Daniel Sneddon <daniel.sneddon@...ux.intel.com>, stable@...r.kernel.org,
 Linus Torvalds <torvalds@...ux-foundation.org>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject: [tip: x86/urgent] x86/cpu: Actually turn off mitigations by default
 for SPECULATION_MITIGATIONS=n

The following commit has been merged into the x86/urgent branch of tip:

Commit-ID:     f337a6a21e2fd67eadea471e93d05dd37baaa9be
Gitweb:        https://git.kernel.org/tip/f337a6a21e2fd67eadea471e93d05dd37baaa9be
Author:        Sean Christopherson <seanjc@...gle.com>
AuthorDate:    Tue, 09 Apr 2024 10:51:05 -07:00
Committer:     Ingo Molnar <mingo@...nel.org>
CommitterDate: Wed, 10 Apr 2024 16:22:47 +02:00

x86/cpu: Actually turn off mitigations by default for SPECULATION_MITIGATIONS=n

Initialize cpu_mitigations to CPU_MITIGATIONS_OFF if the kernel is built
with CONFIG_SPECULATION_MITIGATIONS=n, as the help text quite clearly
states that disabling SPECULATION_MITIGATIONS is supposed to turn off all
mitigations by default.

  │ If you say N, all mitigations will be disabled. You really
  │ should know what you are doing to say so.

As is, the kernel still defaults to CPU_MITIGATIONS_AUTO, which results in
some mitigations being enabled in spite of SPECULATION_MITIGATIONS=n.

Fixes: f43b9876e857 ("x86/retbleed: Add fine grained Kconfig knobs")
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Reviewed-by: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
Cc: stable@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: https://lore.kernel.org/r/20240409175108.1512861-2-seanjc@google.com
---
 kernel/cpu.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 8f6affd..07ad53b 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -3207,7 +3207,8 @@ enum cpu_mitigations {
 };
 
 static enum cpu_mitigations cpu_mitigations __ro_after_init =
-	CPU_MITIGATIONS_AUTO;
+	IS_ENABLED(CONFIG_SPECULATION_MITIGATIONS) ? CPU_MITIGATIONS_AUTO :
+						     CPU_MITIGATIONS_OFF;
 
 static int __init mitigations_parse_cmdline(char *arg)
 {