linux-kernel - [PATCH] x86/virtio: Have SEV guests enforce restricted virtio memory access

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Date:   Thu,  4 Mar 2021 16:40:11 -0600
From:   Tom Lendacky <thomas.lendacky@....com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Brijesh Singh <brijesh.singh@....com>
Subject: [PATCH] x86/virtio: Have SEV guests enforce restricted virtio memory access

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

An SEV guest requires that virtio devices use the DMA API to allow the
hypervisor to successfully access guest memory as needed.

The VIRTIO_F_VERSION_1 and VIRTIO_F_ACCESS_PLATFORM features tell virtio
to use the DMA API. Add arch_has_restricted_virtio_memory_access() for
x86, to fail the device probe if these features have not been set for the
device when running as an SEV guest.

Cc: Brijesh Singh <brijesh.singh@....com>
Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
---
 arch/x86/Kconfig          | 1 +
 arch/x86/mm/mem_encrypt.c | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 2792879d398e..e80e7268d2c6 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1518,6 +1518,7 @@ config AMD_MEM_ENCRYPT
 	select ARCH_USE_MEMREMAP_PROT
 	select ARCH_HAS_FORCE_DMA_UNENCRYPTED
 	select INSTRUCTION_DECODER
+	select ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
 	help
 	  Say yes to enable support for the encryption of system memory.
 	  This requires an AMD processor that supports Secure Memory
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index 4b01f7dbaf30..667283f3dcfa 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -484,3 +484,8 @@ void __init mem_encrypt_init(void)
 	print_mem_encrypt_feature_info();
 }
 
+int arch_has_restricted_virtio_memory_access(void)
+{
+	return sev_active();
+}
+EXPORT_SYMBOL_GPL(arch_has_restricted_virtio_memory_access);
-- 
2.30.0