From c0fecaa44dc341d86e4ce96efcda9ea8b4c106af Mon Sep 17 00:00:00 2001 From: Demi Marie Obenour Date: Thu, 19 Jan 2023 14:03:58 -0500 Subject: [PATCH] efi: Apply allowlist to EFI configuration tables when running under Xen MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Ard Biesheuvel Signed-off-by: Demi Marie Obenour Tested-by: Marek Marczykowski-Górecki Signed-off-by: Ard Biesheuvel --- drivers/firmware/efi/efi.c | 13 ++++++++++--- drivers/xen/efi.c | 25 +++++++++++++++++++++++++ include/linux/efi.h | 10 ++++++++++ 3 files changed, 45 insertions(+), 3 deletions(-) diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c index 90142f6..19c1191 100644 --- a/drivers/firmware/efi/efi.c +++ b/drivers/firmware/efi/efi.c @@ -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; diff --git a/drivers/xen/efi.c b/drivers/xen/efi.c index 3c79235..fb321cd 100644 --- a/drivers/xen/efi.c +++ b/drivers/xen/efi.c @@ -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; + } +} diff --git a/include/linux/efi.h b/include/linux/efi.h index 4d7a44f..1a1adc8 100644 --- a/include/linux/efi.h +++ b/include/linux/efi.h @@ -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 */ -- 2.7.4