[RFC] efi/tpm: add efi.tpm_log as a reserved region in 820_table_firmware

[Usama Arif]

Looking at the TPM spec [1]

If the ACPI TPM2 table contains the address and size of the Platform
Firmware TCG log, firmware “pins” the memory associated with the
Platform FirmwareTCG log, and reports this memory as “Reserved” memory
via the INT 15h/E820 interface.

It looks like the firmware should pass this as reserved in e820 memory
map. However, it doesn't seem to. The firmware being tested on is:
dmidecode -s bios-version
edk2-20240214-2.el9

When this area is not reserved, it comes up as usable in
/sys/firmware/memmap. This means that kexec, which uses that memmap
to find usable memory regions, can select the region where efi.tpm_log
is and overwrite it and relocate_kernel.

Having a fix in firmware can be difficult to get through. As a secondary
fix, this patch marks that region as reserved in e820_table_firmware if it
is currently E820_TYPE_RAM so that kexec doesn't use it for kernel segments.

[1] https://trustedcomputinggroup.org/wp-content/uploads/PC-ClientPlatform_Profile_for_TPM_2p0_Systems_v49_161114_public-review.pdf

Signed-off-by: Usama Arif <usamaarif642 at gmail.com>
---
 arch/x86/include/asm/e820/api.h | 2 ++
 arch/x86/kernel/e820.c          | 6 ++++++
 arch/x86/platform/efi/efi.c     | 9 +++++++++
 drivers/firmware/efi/tpm.c      | 2 +-
 include/linux/efi.h             | 7 +++++++
 5 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/e820/api.h b/arch/x86/include/asm/e820/api.h
index 2e74a7f0e935..4e9aa24f03bd 100644
--- a/arch/x86/include/asm/e820/api.h
+++ b/arch/x86/include/asm/e820/api.h
@@ -16,6 +16,8 @@ extern bool e820__mapped_all(u64 start, u64 end, enum e820_type type);
 
 extern void e820__range_add   (u64 start, u64 size, enum e820_type type);
 extern u64  e820__range_update(u64 start, u64 size, enum e820_type old_type, enum e820_type new_type);
+extern u64  e820__range_update_firmware(u64 start, u64 size, enum e820_type old_type,
+					enum e820_type new_type);
 extern u64  e820__range_remove(u64 start, u64 size, enum e820_type old_type, bool check_type);
 extern u64  e820__range_update_table(struct e820_table *t, u64 start, u64 size, enum e820_type old_type, enum e820_type new_type);
 
diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
index 4893d30ce438..912400161623 100644
--- a/arch/x86/kernel/e820.c
+++ b/arch/x86/kernel/e820.c
@@ -538,6 +538,12 @@ u64 __init e820__range_update_table(struct e820_table *t, u64 start, u64 size,
 	return __e820__range_update(t, start, size, old_type, new_type);
 }
 
+u64 __init e820__range_update_firmware(u64 start, u64 size, enum e820_type old_type,
+				       enum e820_type new_type)
+{
+	return __e820__range_update(e820_table_firmware, start, size, old_type, new_type);
+}
+
 /* Remove a range of memory from the E820 table: */
 u64 __init e820__range_remove(u64 start, u64 size, enum e820_type old_type, bool check_type)
 {
diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 88a96816de9a..aa95f77d7a30 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/arch/x86/platform/efi/efi.c
@@ -171,6 +171,15 @@ static void __init do_add_efi_memmap(void)
 	e820__update_table(e820_table);
 }
 
+/* Reserve firmware area if it was marked as RAM */
+void arch_update_firmware_area(u64 addr, u64 size)
+{
+	if (e820__get_entry_type(addr, addr + size) == E820_TYPE_RAM) {
+		e820__range_update_firmware(addr, size, E820_TYPE_RAM, E820_TYPE_RESERVED);
+		e820__update_table(e820_table_firmware);
+	}
+}
+
 /*
  * Given add_efi_memmap defaults to 0 and there is no alternative
  * e820 mechanism for soft-reserved memory, import the full EFI memory
diff --git a/drivers/firmware/efi/tpm.c b/drivers/firmware/efi/tpm.c
index e8d69bd548f3..8e6e7131d718 100644
--- a/drivers/firmware/efi/tpm.c
+++ b/drivers/firmware/efi/tpm.c
@@ -60,6 +60,7 @@ int __init efi_tpm_eventlog_init(void)
 	}
 
 	tbl_size = sizeof(*log_tbl) + log_tbl->size;
+	arch_update_firmware_area(efi.tpm_log, tbl_size);
 	memblock_reserve(efi.tpm_log, tbl_size);
 
 	if (efi.tpm_final_log == EFI_INVALID_TABLE_ADDR) {
@@ -107,4 +108,3 @@ int __init efi_tpm_eventlog_init(void)
 	early_memunmap(log_tbl, sizeof(*log_tbl));
 	return ret;
 }
-
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 6bf3c4fe8511..9c239cdff771 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1371,4 +1371,11 @@ extern struct blocking_notifier_head efivar_ops_nh;
 void efivars_generic_ops_register(void);
 void efivars_generic_ops_unregister(void);
 
+#ifdef CONFIG_X86_64
+void __init arch_update_firmware_area(u64 addr, u64 size);
+#else
+static inline void __init arch_update_firmware_area(u64 addr, u64 size)
+{
+}
+#endif
 #endif /* _LINUX_EFI_H */
-- 
2.43.5