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x86/kernel: Validate ROM memory before accessing when SEV-SNP is active

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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 the page table.

When SEV-SNP is active, all the private memory must be validated before
accessing. 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
exception yet, so validate the ROM memory regions before it is accessed.

  [ bp: Massage commit message. ]

Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-21-brijesh.singh@amd.com
This commit is contained in:
Brijesh Singh 2022-02-09 12:10:14 -06:00 committed by Borislav Petkov
parent efac0eedfa
commit 9704c07bf9
1 changed files with 12 additions and 1 deletions
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13
arch/x86/kernel/probe_roms.c
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@ -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) {