[Xen-devel] [PATCH v8 23/38] x86/realmode: Decrypt trampoline area if memory encryption is active

[Tom Lendacky <thomas.lendacky@xxxxxxx>]

When Secure Memory Encryption is enabled, the trampoline area must not
be encrypted. A CPU running in real mode will not be able to decrypt
memory that has been encrypted because it will not be able to use addresses
with the memory encryption mask.

Reviewed-by: Borislav Petkov <bp@xxxxxxx>
Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
 arch/x86/realmode/init.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index cd4be19..d6ddc7e 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -1,6 +1,7 @@
 #include <linux/io.h>
 #include <linux/slab.h>
 #include <linux/memblock.h>
+#include <linux/mem_encrypt.h>
 
 #include <asm/set_memory.h>
 #include <asm/pgtable.h>
@@ -59,6 +60,13 @@ static void __init setup_real_mode(void)
 
        base = (unsigned char *)real_mode_header;
 
+       /*
+        * If SME is active, the trampoline area will need to be in
+        * decrypted memory in order to bring up other processors
+        * successfully.
+        */
+       set_memory_decrypted((unsigned long)base, size >> PAGE_SHIFT);
+
        memcpy(base, real_mode_blob, size);
 
        phys_base = __pa(base);


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