x86/sev-es: Check required CPU features for SEV-ES

Make sure the machine supports RDRAND, otherwise there is no trusted
source of randomness in the system.

To also check this in the pre-decompression stage, make has_cpuflag()
not depend on CONFIG_RANDOMIZE_BASE anymore.

Signed-off-by: Martin Radev <[e-mail]>
Signed-off-by: Joerg Roedel <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Reviewed-by: Kees Cook <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/boot/compressed/cpuflags.c

···
 // SPDX-License-Identifier: GPL-2.0
-#ifdef CONFIG_RANDOMIZE_BASE
-
 #include "../cpuflags.c"
 
 bool has_cpuflag(int flag)
···
 
 	return test_bit(flag, cpu.flags);
 }
-
-#endif

arch/x86/boot/compressed/misc.h

···
 			    unsigned long *output,
 			    unsigned long output_size,
 			    unsigned long *virt_addr);
-/* cpuflags.c */
-bool has_cpuflag(int flag);
 #else
 static inline void choose_random_location(unsigned long input,
 					  unsigned long input_size,
···
 {
 }
 #endif
+
+/* cpuflags.c */
+bool has_cpuflag(int flag);
 
 #ifdef CONFIG_X86_64
 extern int set_page_decrypted(unsigned long address);

arch/x86/boot/compressed/sev-es.c

···
 	if (!boot_ghcb)
 		return;
 
+	if (!sev_es_check_cpu_features())
+		error("SEV-ES CPU Features missing.");
+
 	/*
 	 * GHCB Page must be flushed from the cache and mapped encrypted again.
 	 * Otherwise the running kernel will see strange cache effects when

arch/x86/kernel/sev-es-shared.c

···
  * and is included directly into both code-bases.
  */
 
+#ifndef __BOOT_COMPRESSED
+#define error(v)	pr_err(v)
+#define has_cpuflag(f)	boot_cpu_has(f)
+#endif
+
+static bool __init sev_es_check_cpu_features(void)
+{
+	if (!has_cpuflag(X86_FEATURE_RDRAND)) {
+		error("RDRAND instruction not supported - no trusted source of randomness available\n");
+		return false;
+	}
+
+	return true;
+}
+
 static void sev_es_terminate(unsigned int reason)
 {
 	u64 val = GHCB_SEV_TERMINATE;

arch/x86/kernel/sev-es.c

···
 	if (!sev_es_active())
 		return;
 
+	if (!sev_es_check_cpu_features())
+		panic("SEV-ES CPU Features missing");
+
 	/* Enable SEV-ES special handling */
 	static_branch_enable(&sev_es_enable_key);