[PATCH Part1 RFC v4 14/36] x86/kernel: Validate rom memory before accessing when SEV-SNP is active
From: Brijesh Singh <hidden>
Date: 2021-07-07 18:16:47
Also in:
kvm, linux-coco, linux-efi, linux-mm, lkml, platform-driver-x86
Subsystem:
the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
The probe_roms() access 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 <redacted> --- arch/x86/kernel/probe_roms.c | 13 ++++++++++++- 1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/probe_roms.c b/arch/x86/kernel/probe_roms.c
index 9e1def3744f2..9c09df86d167 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 is not part of the E820 system RAM and is not pre-validated + * by the BIOS. The kernel page table maps the ROM region as encrypted memory, + * the SEV-SNP requires the encrypted memory must be validated before the + * access. Validate the ROM before accessing it. + */ + 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) {
--
2.17.1