[tip: x86/alternatives] x86/alternatives: Catch late X86_FEATURE modifiers

[tip-bot2 for Borislav Petkov (AMD)]

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

Commit-ID:     97784e52f18fe6e0d6516ded8ecd3cec722ce9cc
Gitweb:        https://git.kernel.org/tip/97784e52f18fe6e0d6516ded8ecd3cec722ce9cc
Author:        Borislav Petkov (AMD) <bp@xxxxxxxxx>
AuthorDate:    Wed, 27 Mar 2024 16:43:14 +01:00
Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
CommitterDate: Wed, 03 Apr 2024 20:03:24 +02:00

x86/alternatives: Catch late X86_FEATURE modifiers

After alternatives have been patched, changes to the X86_FEATURE flags
won't take effect and could potentially even be wrong.

Warn about it.

This is something which has been long overdue.

Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
Tested-by: Srikanth Aithal <sraithal@xxxxxxx>
Link: https://lore.kernel.org/r/20240327154317.29909-3-bp@xxxxxxxxx
---
 arch/x86/include/asm/cpufeature.h | 8 ++++++--
 arch/x86/kernel/cpu/cpuid-deps.c  | 3 +++
 2 files changed, 9 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index 7103ba1..e5d8880 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -148,8 +148,12 @@ extern const char * const x86_bug_flags[NBUGINTS*32];
 extern void setup_clear_cpu_cap(unsigned int bit);
 extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
 
-#define setup_force_cpu_cap(bit) do { \
-	set_cpu_cap(&boot_cpu_data, bit);	\
+#define setup_force_cpu_cap(bit) do {			\
+							\
+	if (!boot_cpu_has(bit))				\
+		WARN_ON(alternatives_patched);		\
+							\
+	set_cpu_cap(&boot_cpu_data, bit);		\
 	set_bit(bit, (unsigned long *)cpu_caps_set);	\
 } while (0)
 
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index b717420..5dd427c 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -114,6 +114,9 @@ static void do_clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int feature)
 	if (WARN_ON(feature >= MAX_FEATURE_BITS))
 		return;
 
+	if (boot_cpu_has(feature))
+		WARN_ON(alternatives_patched);
+
 	clear_feature(c, feature);
 
 	/* Collect all features to disable, handling dependencies */