[PATCH 2/5] x86/alternatives: Catch late X86_FEATURE modifiers

Borislav Petkov
2024-03-27T15:43:57Z

From: "Borislav Petkov (AMD)" <bp@alien8.de>

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@alien8.de>
---
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 1ef620d508f4..d0b9c411144b 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -146,8 +146,12 @@ 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 b7174209d855..5dd427c6feb2 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 */
--
2.43.0