diff mbox series

[v12,20/46] x86/kernel: Validate ROM memory before accessing when SEV-SNP is active

Message ID 20220307213356.2797205-21-brijesh.singh@amd.com
State Accepted
Commit 9704c07bf9f7682a83aec4e66f2d9154dbd8577f
Headers show
Series Add AMD Secure Nested Paging (SEV-SNP) Guest Support | expand

Commit Message

Brijesh Singh March 7, 2022, 9:33 p.m. UTC 
probe_roms() accesses the memory range (0xc0000 - 0x10000) to probe
various ROMs. The memory range is not part of the E820 system RAM
range. The memory range is mapped as private (i.e encrypted) in page
table.

When SEV-SNP is active, all the private memory must be validated before
the access. The ROM range was not part of E820 map, so the guest BIOS
did not validate it. An access to invalidated memory will cause a VC
exception. The guest does not support handling not-validated VC exception
yet, so validate the ROM memory regions before it is accessed.

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
---
 arch/x86/kernel/probe_roms.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/x86/kernel/probe_roms.c b/arch/x86/kernel/probe_roms.c
index 36e84d904260..319fef37d9dc 100644
--- a/arch/x86/kernel/probe_roms.c
+++ b/arch/x86/kernel/probe_roms.c
@@ -21,6 +21,7 @@ 
 #include <asm/sections.h>
 #include <asm/io.h>
 #include <asm/setup_arch.h>
+#include <asm/sev.h>
 
 static struct resource system_rom_resource = {
 	.name	= "System ROM",
@@ -197,11 +198,21 @@  static int __init romchecksum(const unsigned char *rom, unsigned long length)
 
 void __init probe_roms(void)
 {
-	const unsigned char *rom;
 	unsigned long start, length, upper;
+	const unsigned char *rom;
 	unsigned char c;
 	int i;
 
+	/*
+	 * The ROM memory range is not part of the e820 table and is therefore not
+	 * pre-validated by BIOS. The kernel page table maps the ROM region as encrypted
+	 * memory, and SNP requires encrypted memory to be validated before access.
+	 * Do that here.
+	 */
+	snp_prep_memory(video_rom_resource.start,
+			((system_rom_resource.end + 1) - video_rom_resource.start),
+			SNP_PAGE_STATE_PRIVATE);
+
 	/* video rom */
 	upper = adapter_rom_resources[0].start;
 	for (start = video_rom_resource.start; start < upper; start += 2048) {