Re: [PATCH v4 04/39] x86/cpufeatures: Enable CET CR4 bit for shadow stack

[Borislav Petkov]

On Fri, Dec 02, 2022 at 04:35:31PM -0800, Rick Edgecombe wrote:
> From: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
> 
> Setting CR4.CET is a prerequisite for utilizing any CET features, most of
> which also require setting MSRs.

...

>  arch/x86/kernel/cpu/common.c | 37 ++++++++++++++++++++++++++++++------
>  1 file changed, 31 insertions(+), 6 deletions(-)

Looks better.

Let's get rid of the ifdeffery and simplify it even more. Diff ontop:

---

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 579f10222432..c364f3067121 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -597,12 +597,14 @@ __noendbr void ibt_restore(u64 save)
 
 #endif
 
-#ifdef CONFIG_X86_CET
 static __always_inline void setup_cet(struct cpuinfo_x86 *c)
 {
-	bool kernel_ibt = HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT);
-	bool user_shstk;
-	u64 msr = 0;
+	bool kernel_ibt, user_shstk;
+
+	if (!IS_ENABLED(CONFIG_X86_CET))
+		return;
+
+	kernel_ibt = HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT);
 
 	/*
 	 * Enable user shadow stack only if the Linux defined user shadow stack
@@ -618,21 +620,18 @@ static __always_inline void setup_cet(struct cpuinfo_x86 *c)
 		set_cpu_cap(c, X86_FEATURE_USER_SHSTK);
 
 	if (kernel_ibt)
-		msr = CET_ENDBR_EN;
+		wrmsrl(MSR_IA32_S_CET, CET_ENDBR_EN);
+	else
+		wrmsrl(MSR_IA32_S_CET, 0);
 
-	wrmsrl(MSR_IA32_S_CET, msr);
 	cr4_set_bits(X86_CR4_CET);
 
 	if (kernel_ibt && !ibt_selftest()) {
 		pr_err("IBT selftest: Failed!\n");
 		wrmsrl(MSR_IA32_S_CET, 0);
 		setup_clear_cpu_cap(X86_FEATURE_IBT);
-		return;
 	}
 }
-#else /* CONFIG_X86_CET */
-static inline void setup_cet(struct cpuinfo_x86 *c) {}
-#endif
 
 __noendbr void cet_disable(void)
 {

-- 
Regards/Gruss,
    Boris.

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