linux-kernel - [RFC PATCH v1 11/28] x86: Don't decrypt trampoline area if SEV is active

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Message-ID: <147190835102.9523.9786544054464015663.stgit@brijesh-build-machine>
Date:   Mon, 22 Aug 2016 19:25:51 -0400
From:   Brijesh Singh <brijesh.singh@....com>
To:     <simon.guinot@...uanux.org>, <linux-efi@...r.kernel.org>,
        <brijesh.singh@....com>, <kvm@...r.kernel.org>,
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Subject: [RFC PATCH v1 11/28] x86: Don't decrypt trampoline area if SEV is
 active

From: Tom Lendacky <thomas.lendacky@....com>

When Secure Encrypted Virtualization is active instruction fetches are
always interpreted as being from encrypted memory so the trampoline area
must remain encrypted when SEV is active.

Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/realmode/init.c |    9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/realmode/init.c b/arch/x86/realmode/init.c
index c3edb49..f3207e5 100644
--- a/arch/x86/realmode/init.c
+++ b/arch/x86/realmode/init.c
@@ -138,10 +138,13 @@ static void __init set_real_mode_permissions(void)
 	/*
 	 * If memory encryption is active, the trampoline area will need to
 	 * be in non-encrypted memory in order to bring up other processors
-	 * successfully.
+	 * successfully. This only applies to SME, SEV requires the trampoline
+	 * to be encrypted.
 	 */
-	sme_early_mem_dec(__pa(base), size);
-	sme_set_mem_dec(base, size);
+	if (!sev_active) {
+		sme_early_mem_dec(__pa(base), size);
+		sme_set_mem_dec(base, size);
+	}
 
 	set_memory_nx((unsigned long) base, size >> PAGE_SHIFT);
 	set_memory_ro((unsigned long) base, ro_size >> PAGE_SHIFT);