Re: [PATCH v3 5/8] x86/sme: Replace occurrences of sme_active() with cc_platform_has()

[Borislav Petkov <bp@alien8.de>]

On Thu, Sep 23, 2021 at 12:05:58AM +0300, Kirill A. Shutemov wrote:
> Unless we find other way to guarantee RIP-relative access, we must use
> fixup_pointer() to access any global variables.

Yah, I've asked compiler folks about any guarantees we have wrt
rip-relative addresses but it doesn't look good. Worst case, we'd have
to do the fixup_pointer() thing.

In the meantime, Tom and I did some more poking at this and here's a
diff ontop.

The direction being that we'll stick both the AMD and Intel
*cc_platform_has() call into cc_platform.c for which instrumentation
will be disabled so no issues with that.

And that will keep all that querying all together in a single file.

---
diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
index a73712b6ee0e..2d4f5c17d79c 100644
--- a/arch/x86/include/asm/mem_encrypt.h
+++ b/arch/x86/include/asm/mem_encrypt.h
@@ -51,7 +51,6 @@ void __init mem_encrypt_free_decrypted_mem(void);
 void __init mem_encrypt_init(void);
 
 void __init sev_es_init_vc_handling(void);
-bool amd_cc_platform_has(enum cc_attr attr);
 
 #define __bss_decrypted __section(".bss..decrypted")
 
@@ -74,7 +73,6 @@ static inline void __init sme_encrypt_kernel(struct boot_params *bp) { }
 static inline void __init sme_enable(struct boot_params *bp) { }
 
 static inline void sev_es_init_vc_handling(void) { }
-static inline bool amd_cc_platform_has(enum cc_attr attr) { return false; }
 
 static inline int __init
 early_set_memory_decrypted(unsigned long vaddr, unsigned long size) { return 0; }
@@ -103,12 +101,6 @@ static inline u64 sme_get_me_mask(void)
 	return sme_me_mask;
 }
 
-#if defined(CONFIG_CPU_SUP_INTEL) && defined(CONFIG_ARCH_HAS_CC_PLATFORM)
-bool intel_cc_platform_has(enum cc_attr attr);
-#else
-static inline bool intel_cc_platform_has(enum cc_attr attr) { return false; }
-#endif
-
 #endif	/* __ASSEMBLY__ */
 
 #endif	/* __X86_MEM_ENCRYPT_H__ */
diff --git a/arch/x86/kernel/cc_platform.c b/arch/x86/kernel/cc_platform.c
index da54a1805211..97ede7052f77 100644
--- a/arch/x86/kernel/cc_platform.c
+++ b/arch/x86/kernel/cc_platform.c
@@ -13,6 +13,52 @@
 
 #include <asm/processor.h>
 
+static bool intel_cc_platform_has(enum cc_attr attr)
+{
+#ifdef CONFIG_INTEL_TDX_GUEST
+	return false;
+#else
+	return false;
+#endif
+}
+
+/*
+ * SME and SEV are very similar but they are not the same, so there are
+ * times that the kernel will need to distinguish between SME and SEV. The
+ * cc_platform_has() function is used for this.  When a distinction isn't
+ * needed, the CC_ATTR_MEM_ENCRYPT attribute can be used.
+ *
+ * The trampoline code is a good example for this requirement.  Before
+ * paging is activated, SME will access all memory as decrypted, but SEV
+ * will access all memory as encrypted.  So, when APs are being brought
+ * up under SME the trampoline area cannot be encrypted, whereas under SEV
+ * the trampoline area must be encrypted.
+ */
+static bool amd_cc_platform_has(enum cc_attr attr)
+{
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	switch (attr) {
+	case CC_ATTR_MEM_ENCRYPT:
+		return sme_me_mask;
+
+	case CC_ATTR_HOST_MEM_ENCRYPT:
+		return sme_me_mask && !(sev_status & MSR_AMD64_SEV_ENABLED);
+
+	case CC_ATTR_GUEST_MEM_ENCRYPT:
+		return sev_status & MSR_AMD64_SEV_ENABLED;
+
+	case CC_ATTR_GUEST_STATE_ENCRYPT:
+		return sev_status & MSR_AMD64_SEV_ES_ENABLED;
+
+	default:
+		return false;
+	}
+#else
+	return false;
+#endif
+}
+
+
 bool cc_platform_has(enum cc_attr attr)
 {
 	if (sme_me_mask)
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 53756ff12295..8321c43554a1 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -60,13 +60,6 @@ static u64 msr_test_ctrl_cache __ro_after_init;
  */
 static bool cpu_model_supports_sld __ro_after_init;
 
-#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
-bool intel_cc_platform_has(enum cc_attr attr)
-{
-	return false;
-}
-#endif
-
 /*
  * Processors which have self-snooping capability can handle conflicting
  * memory type across CPUs by snooping its own cache. However, there exists
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 9417d404ea92..23d54b810f08 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -361,38 +361,6 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
 	return early_set_memory_enc_dec(vaddr, size, true);
 }
 
-/*
- * SME and SEV are very similar but they are not the same, so there are
- * times that the kernel will need to distinguish between SME and SEV. The
- * cc_platform_has() function is used for this.  When a distinction isn't
- * needed, the CC_ATTR_MEM_ENCRYPT attribute can be used.
- *
- * The trampoline code is a good example for this requirement.  Before
- * paging is activated, SME will access all memory as decrypted, but SEV
- * will access all memory as encrypted.  So, when APs are being brought
- * up under SME the trampoline area cannot be encrypted, whereas under SEV
- * the trampoline area must be encrypted.
- */
-bool amd_cc_platform_has(enum cc_attr attr)
-{
-	switch (attr) {
-	case CC_ATTR_MEM_ENCRYPT:
-		return sme_me_mask;
-
-	case CC_ATTR_HOST_MEM_ENCRYPT:
-		return sme_me_mask && !(sev_status & MSR_AMD64_SEV_ENABLED);
-
-	case CC_ATTR_GUEST_MEM_ENCRYPT:
-		return sev_status & MSR_AMD64_SEV_ENABLED;
-
-	case CC_ATTR_GUEST_STATE_ENCRYPT:
-		return sev_status & MSR_AMD64_SEV_ES_ENABLED;
-
-	default:
-		return false;
-	}
-}
-
 /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
 bool force_dma_unencrypted(struct device *dev)
 {

-- 
Regards/Gruss,
    Boris.

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