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efi: Apply allowlist to EFI configuration tables when running under Xen

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As it turns out, Xen does not guarantee that EFI boot services data
regions in memory are preserved, which means that EFI configuration
tables pointing into such memory regions may be corrupted before the
dom0 OS has had a chance to inspect them.

This is causing problems for Qubes OS when it attempts to perform system
firmware updates, which requires that the contents of the EFI System
Resource Table are valid when the fwupd userspace program runs.

However, other configuration tables such as the memory attributes table
or the runtime properties table are equally affected, and so we need a
comprehensive workaround that works for any table type.

So when running under Xen, check the EFI memory descriptor covering the
start of the table, and disregard the table if it does not reside in
memory that is preserved by Xen.

Co-developed-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
This commit is contained in:
Demi Marie Obenour 2023-01-19 14:03:58 -05:00 committed by Ard Biesheuvel
parent aca1d27ac3
commit c0fecaa44d
3 changed files with 45 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

13
drivers/firmware/efi/efi.c
View File

@ -589,13 +589,20 @@ static __init int match_config_table(const efi_guid_t *guid,
int i;
for (i = 0; efi_guidcmp(table_types[i].guid, NULL_GUID); i++) {
if (!efi_guidcmp(*guid, table_types[i].guid)) {
*(table_types[i].ptr) = table;
if (efi_guidcmp(*guid, table_types[i].guid))
continue;
if (!efi_config_table_is_usable(guid, table)) {
if (table_types[i].name[0])
pr_cont("%s=0x%lx ",
pr_cont("(%s=0x%lx unusable) ",
table_types[i].name, table);
return 1;
}
*(table_types[i].ptr) = table;
if (table_types[i].name[0])
pr_cont("%s=0x%lx ", table_types[i].name, table);
return 1;
}
return 0;

25
drivers/xen/efi.c
View File

@ -328,3 +328,28 @@ int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
return 0;
}
bool __init xen_efi_config_table_is_usable(const efi_guid_t *guid,
unsigned long table)
{
efi_memory_desc_t md;
int rc;
if (!efi_enabled(EFI_PARAVIRT))
return true;
rc = efi_mem_desc_lookup(table, &md);
if (rc)
return false;
switch (md.type) {
case EFI_RUNTIME_SERVICES_CODE:
case EFI_RUNTIME_SERVICES_DATA:
case EFI_ACPI_RECLAIM_MEMORY:
case EFI_ACPI_MEMORY_NVS:
case EFI_RESERVED_TYPE:
return true;
default:
return false;
}
}

10
include/linux/efi.h
View File

@ -1322,4 +1322,14 @@ struct linux_efi_initrd {
/* Header of a populated EFI secret area */
#define EFI_SECRET_TABLE_HEADER_GUID EFI_GUID(0x1e74f542, 0x71dd, 0x4d66, 0x96, 0x3e, 0xef, 0x42, 0x87, 0xff, 0x17, 0x3b)
bool xen_efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table);
static inline
bool efi_config_table_is_usable(const efi_guid_t *guid, unsigned long table)
{
if (!IS_ENABLED(CONFIG_XEN_EFI))
return true;
return xen_efi_config_table_is_usable(guid, table);
}
#endif /* _LINUX_EFI_H */