x86/boot/realmode: Check for memory encryption on the APs

Add support to check if memory encryption is active in the kernel and that
it has been enabled on the AP. If memory encryption is active in the kernel
but has not been enabled on the AP, then set the memory encryption bit (bit
23) of MSR_K8_SYSCFG to enable memory encryption on that AP and allow the
AP to continue start up.

Signed-off-by: Tom Lendacky <[email protected]>
Reviewed-by: Thomas Gleixner <[email protected]>
Reviewed-by: Borislav Petkov <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Andrey Ryabinin <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brijesh Singh <[email protected]>
Cc: Dave Young <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Larry Woodman <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Matt Fleming <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Paolo Bonzini <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Radim Krčmář <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Toshimitsu Kani <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Link: http://lkml.kernel.org/r/37e29b99c395910f56ca9f8ecf7b0439b28827c8.1500319216.git.thomas.lendacky@amd.com
Signed-off-by: Ingo Molnar <[email protected]>

3 files changed, 40 insertions, 0 deletions

diff --git a/arch/x86/include/asm/realmode.h b/arch/x86/include/asm/realmode.h
index 230e1903acf0..90d91520c13a 100644
--- a/arch/x86/include/asm/realmode.h
+++ b/arch/x86/include/asm/realmode.h
@@ -1,6 +1,15 @@
 #ifndef _ARCH_X86_REALMODE_H
 #define _ARCH_X86_REALMODE_H
 
+/*
+ * Flag bit definitions for use with the flags field of the trampoline header
+ * in the CONFIG_X86_64 variant.
+ */
+#define TH_FLAGS_SME_ACTIVE_BIT		0
+#define TH_FLAGS_SME_ACTIVE		BIT(TH_FLAGS_SME_ACTIVE_BIT)
+
+#ifndef __ASSEMBLY__
+
 #include <linux/types.h>
 #include <asm/io.h>
 
@@ -38,6 +47,7 @@ struct trampoline_header {
 	u64 start;
 	u64 efer;
 	u32 cr4;
+	u32 flags;
 #endif
 };
 
@@ -69,4 +79,6 @@ static inline size_t real_mode_size_needed(void)
 void set_real_mode_mem(phys_addr_t mem, size_t size);
 void reserve_real_mode(void);
 
+#endif /* __ASSEMBLY__ */
+
 #endif /* _ARCH_X86_REALMODE_H */
diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index d6ddc7e60884..1f71980fc5e0 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -108,6 +108,10 @@ static void __init setup_real_mode(void)
 	trampoline_cr4_features = &trampoline_header->cr4;
 	*trampoline_cr4_features = mmu_cr4_features;
 
+	trampoline_header->flags = 0;
+	if (sme_active())
+		trampoline_header->flags |= TH_FLAGS_SME_ACTIVE;
+
 	trampoline_pgd = (u64 *) __va(real_mode_header->trampoline_pgd);
 	trampoline_pgd[0] = trampoline_pgd_entry.pgd;
 	trampoline_pgd[511] = init_top_pgt[511].pgd;
diff --git a/arch/x86/realmode/rm/trampoline_64.S b/arch/x86/realmode/rm/trampoline_64.S
index dac7b20d2f9d..614fd7064d0a 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -30,6 +30,7 @@
 #include <asm/msr.h>
 #include <asm/segment.h>
 #include <asm/processor-flags.h>
+#include <asm/realmode.h>
 #include "realmode.h"
 
 	.text
@@ -92,6 +93,28 @@ ENTRY(startup_32)
 	movl	%edx, %fs
 	movl	%edx, %gs
 
+	/*
+	 * Check for memory encryption support. This is a safety net in
+	 * case BIOS hasn't done the necessary step of setting the bit in
+	 * the MSR for this AP. If SME is active and we've gotten this far
+	 * then it is safe for us to set the MSR bit and continue. If we
+	 * don't we'll eventually crash trying to execute encrypted
+	 * instructions.
+	 */
+	bt	$TH_FLAGS_SME_ACTIVE_BIT, pa_tr_flags
+	jnc	.Ldone
+	movl	$MSR_K8_SYSCFG, %ecx
+	rdmsr
+	bts	$MSR_K8_SYSCFG_MEM_ENCRYPT_BIT, %eax
+	jc	.Ldone
+
+	/*
+	 * Memory encryption is enabled but the SME enable bit for this
+	 * CPU has has not been set.  It is safe to set it, so do so.
+	 */
+	wrmsr
+.Ldone:
+
 	movl	pa_tr_cr4, %eax
 	movl	%eax, %cr4		# Enable PAE mode
 
@@ -147,6 +170,7 @@ GLOBAL(trampoline_header)
 	tr_start:		.space	8
 	GLOBAL(tr_efer)		.space	8
 	GLOBAL(tr_cr4)		.space	4
+	GLOBAL(tr_flags)	.space	4
 END(trampoline_header)
 
 #include "trampoline_common.S"