kernel/SOURCES/1046-x86-bugs-Make-sure-MSR_SPEC_CTRL-is-updated-properly.patch

From 97e9891f4f6253ec70fc870e639d7e4d07b9e361 Mon Sep 17 00:00:00 2001
From: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Date: Wed, 30 Nov 2022 07:25:51 -0800
Subject: [PATCH 32/36] x86/bugs: Make sure MSR_SPEC_CTRL is updated properly
 upon resume from S3

The "force" argument to write_spec_ctrl_current() is currently ambiguous
as it does not guarantee the MSR write. This is due to the optimization
that writes to the MSR happen only when the new value differs from the
cached value.

This is fine in most cases, but breaks for S3 resume when the cached MSR
value gets out of sync with the hardware MSR value due to S3 resetting
it.

When x86_spec_ctrl_current is same as x86_spec_ctrl_base, the MSR write
is skipped. Which results in SPEC_CTRL mitigations not getting restored.

Move the MSR write from write_spec_ctrl_current() to a new function that
unconditionally writes to the MSR. Update the callers accordingly and
rename functions.

  [ bp: Rework a bit. ]

Fixes: caa0ff24d5d0 ("x86/bugs: Keep a per-CPU IA32_SPEC_CTRL value")
Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: <stable@kernel.org>
Link: https://lore.kernel.org/r/806d39b0bfec2fe8f50dc5446dff20f5bb24a959.1669821572.git.pawan.kumar.gupta@linux.intel.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
(cherry picked from commit 66065157420c5b9b3f078f43d313c153e1ff7f83)
Signed-off-by: Mridula Shastry <mridula.c.shastry@oracle.com>
Reviewed-by: Todd Vierling <todd.vierling@oracle.com>
---
 arch/x86/include/asm/nospec-branch.h |  2 +-
 arch/x86/kernel/cpu/bugs.c           | 21 ++++++++++++++-------
 arch/x86/kernel/process.c            |  2 +-
 3 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
index 442e62e7be47..53e56fc9cf70 100644
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -318,7 +318,7 @@ static inline void indirect_branch_prediction_barrier(void)
 /* The Intel SPEC CTRL MSR base value cache */
 extern u64 x86_spec_ctrl_base;
 DECLARE_PER_CPU(u64, x86_spec_ctrl_current);
-extern void write_spec_ctrl_current(u64 val, bool force);
+extern void update_spec_ctrl_cond(u64 val);
 extern u64 spec_ctrl_current(void);
 
 /*
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 5dc79427d047..53623ea69873 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -60,11 +60,18 @@ EXPORT_SYMBOL_GPL(x86_spec_ctrl_current);
 
 static DEFINE_MUTEX(spec_ctrl_mutex);
 
+/* Update SPEC_CTRL MSR and its cached copy unconditionally */
+static void update_spec_ctrl(u64 val)
+{
+	this_cpu_write(x86_spec_ctrl_current, val);
+	wrmsrl(MSR_IA32_SPEC_CTRL, val);
+}
+
 /*
  * Keep track of the SPEC_CTRL MSR value for the current task, which may differ
  * from x86_spec_ctrl_base due to STIBP/SSB in __speculation_ctrl_update().
  */
-void write_spec_ctrl_current(u64 val, bool force)
+void update_spec_ctrl_cond(u64 val)
 {
 	if (this_cpu_read(x86_spec_ctrl_current) == val)
 		return;
@@ -76,7 +83,7 @@ void write_spec_ctrl_current(u64 val, bool force)
 	 * forced or the exit MSR write is skipped the update can be delayed
 	 * until that time.
 	 */
-	if (force || !cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) ||
+	if (!cpu_feature_enabled(X86_FEATURE_KERNEL_IBRS) ||
 	    cpu_feature_enabled(X86_FEATURE_IBRS_EXIT_SKIP))
 		wrmsrl(MSR_IA32_SPEC_CTRL, val);
 }
@@ -1308,7 +1315,7 @@ static void __init spec_ctrl_disable_kernel_rrsba(void)
 
 	if (ia32_cap & ARCH_CAP_RRSBA) {
 		x86_spec_ctrl_base |= SPEC_CTRL_RRSBA_DIS_S;
-		write_spec_ctrl_current(x86_spec_ctrl_base, true);
+		update_spec_ctrl(x86_spec_ctrl_base);
 	}
 }
 
@@ -1440,7 +1447,7 @@ static void __init spectre_v2_select_mitigation(void)
 
 	if (spectre_v2_in_ibrs_mode(mode)) {
 		x86_spec_ctrl_base |= SPEC_CTRL_IBRS;
-		write_spec_ctrl_current(x86_spec_ctrl_base, true);
+		update_spec_ctrl(x86_spec_ctrl_base);
 	}
 
 	switch (mode) {
@@ -1565,7 +1572,7 @@ static void __init spectre_v2_select_mitigation(void)
 static void update_stibp_msr(void * __unused)
 {
 	u64 val = spec_ctrl_current() | (x86_spec_ctrl_base & SPEC_CTRL_STIBP);
-	write_spec_ctrl_current(val, true);
+	update_spec_ctrl(val);
 }
 
 /* Update x86_spec_ctrl_base in case SMT state changed. */
@@ -1798,7 +1805,7 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void)
 			x86_amd_ssb_disable();
 		} else {
 			x86_spec_ctrl_base |= SPEC_CTRL_SSBD;
-			write_spec_ctrl_current(x86_spec_ctrl_base, true);
+			update_spec_ctrl(x86_spec_ctrl_base);
 		}
 	}
 
@@ -2016,7 +2023,7 @@ int arch_prctl_spec_ctrl_get(struct task_struct *task, unsigned long which)
 void x86_spec_ctrl_setup_ap(void)
 {
 	if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
-		write_spec_ctrl_current(x86_spec_ctrl_base, true);
+		update_spec_ctrl(x86_spec_ctrl_base);
 
 	if (ssb_mode == SPEC_STORE_BYPASS_DISABLE)
 		x86_amd_ssb_disable();
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 87bcb25ff8b2..a62f200aa736 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -583,7 +583,7 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp,
 	}
 
 	if (updmsr)
-		write_spec_ctrl_current(msr, false);
+		update_spec_ctrl_cond(msr);
 }
 
 static unsigned long speculation_ctrl_update_tif(struct task_struct *tsk)
-- 
2.39.3