[PATCH 2/2] efi: runtime: accept 1:1 mappings in SetVirtualAddressMap

[Ahmad Fatoum <a.fatoum@barebox.org>]

We do not support SetVirtualAddressMap() and UEFI v2.8 permits
this as long as our EFI_RT_PROPERTIES_TABLE doesn't claim
EFI_RT_SUPPORTED_SET_VIRTUAL_ADDRESS_MAP, which we adhere to[1].

NetBSD's efiboot doesn't seem to care for lack of this bit and
calls SetVirtualAddressMap() unconditionally[2]. This will return with
an error, which has NetBSD call printf() _after_ ExitBootServices[3]
leading to a crash[4].

Fortunately, barebox is not the only firmware that doesn't implement
a full-fledged SetVirtualAddressMap().
Quoting NetBSD commit 41096fd ("efiboot: Use 1:1 PA to VA mappings for
RT services.")[5]:

| UEFI firmware on Snapdragon X Elite devices crashes when
| SetVirtualAddressMap is called with runtime mappings that are not 1:1.
| Always do this on arm64 as it won't interfere with KVA and will help us
| avoid avoid a very common class of firmware bugs.

This means we have an easy way for barebox to workaround this:
Instead of returning EFI_UNSUPPORTED unconditionally, we can handle the
trivial identity mapping case specially and report EFI_SUCCESS for it.

While NetBSD doesn't need it, also implement a 1:1 ConvertPointer for
good measure.

[1]: https://uefi.org/specs/UEFI/2.10/04_EFI_System_Table.html
[2]: https://github.com/NetBSD/src/blob/41096fd/sys/stand/efiboot/efiboot.c#L135
[3]: https://github.com/NetBSD/src/blob/41096fd/sys/stand/efiboot/efifdt.c#L813
[4]: https://gnats.netbsd.org/60890
[5]: https://github.com/NetBSD/src/commit/41096fd4f7bac2ade3f29e9e6e00951aef9e16ce

Reported-by: Johannes Schauer Marin Rodrigues <josch@debian.org>
Signed-off-by: Ahmad Fatoum <a.fatoum@barebox.org>
---
 efi/runtime/services.c | 67 ++++++++++++++++++++++++++++++++++++++++--
 include/efi/memory.h   |  6 ++++
 include/efi/services.h |  2 ++
 3 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/efi/runtime/services.c b/efi/runtime/services.c
index dc4960ac4763..ca60ae512a2d 100644
--- a/efi/runtime/services.c
+++ b/efi/runtime/services.c
@@ -171,17 +171,80 @@ static efi_status_t EFIAPI efirt_set_wakeup_time(char enabled,
 	return efirt_unimplemented();
 }
 
+/**
+ * efirt_set_virtual_address_map() - change from physical to virtual mapping
+ *
+ * This function implements the SetVirtualAddressMap() runtime service.
+ * The barebox runtime isn't relocated and only an identity mapping
+ * is accepted.
+ *
+ * We intentionally don't announce support via the EFI_RT_PROPERTIES_TABLE,
+ * so only operating systems that ignore the table would end up here.
+ * If they configure a 1:1 mapping like NetBSD, we tolerate it and return
+ * success.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @memory_map_size:	size of the virtual map
+ * @descriptor_size:	size of an entry in the map
+ * @descriptor_version:	version of the map entries
+ * @virtmap:		virtual address mapping information
+ * Return:		status code
+ */
 static efi_status_t EFIAPI efirt_set_virtual_address_map(size_t memory_map_size,
 							 size_t descriptor_size,
 							 uint32_t descriptor_version,
 							 struct efi_memory_desc *virtmap)
 {
-	return efirt_unimplemented();
+	static bool efirt_virtmap_set;
+
+	EFI_ENTRY(L"");
+
+	if (efirt_virtmap_set)
+		return EFI_EXIT(EFI_UNSUPPORTED);
+
+	if (descriptor_version != EFI_MEMORY_DESCRIPTOR_VERSION ||
+	    descriptor_size < sizeof(*virtmap))
+		return EFI_EXIT(EFI_INVALID_PARAMETER);
+
+	for (size_t off = 0; off < memory_map_size; off += descriptor_size) {
+		struct efi_memory_desc *md = (void *)virtmap + off;
+
+		if ((md->attrs & EFI_MEMORY_RUNTIME) &&
+		    efi_memory_desc_relocation_offset(md) != 0)
+			return EFI_EXIT(EFI_UNSUPPORTED);
+	}
+
+	efirt_virtmap_set = true;
+
+	return EFI_EXIT(EFI_SUCCESS);
 }
 
+/**
+ * efirt_convert_pointer() - convert pointer to virtual address
+ *
+ * This function implements the ConvertPointer() runtime service.
+ * Only identity mappings are accepted, so the pointer is left as-is.
+ *
+ * See the Unified Extensible Firmware Interface (UEFI) specification for
+ * details.
+ *
+ * @dbg:	EFI_OPTIONAL_PTR if the pointer may be NULL
+ * @address:	pointer to be converted
+ * Return:	status code
+ */
 static efi_status_t EFIAPI efirt_convert_pointer(unsigned long dbg, void **address)
 {
-	return efirt_unimplemented();
+	EFI_ENTRY(L"");
+
+	if (!address)
+		return EFI_EXIT(EFI_INVALID_PARAMETER);
+
+	if (!*address && !(dbg & EFI_OPTIONAL_PTR))
+		return EFI_EXIT(EFI_INVALID_PARAMETER);
+
+	return EFI_EXIT(EFI_SUCCESS);
 }
 
 static efi_status_t EFIAPI
diff --git a/include/efi/memory.h b/include/efi/memory.h
index 74e714099021..336d2a730c1c 100644
--- a/include/efi/memory.h
+++ b/include/efi/memory.h
@@ -91,4 +91,10 @@ struct efi_memory_desc {
 
 #define EFI_MEMORY_DESCRIPTOR_VERSION	1
 
+static inline ptrdiff_t
+efi_memory_desc_relocation_offset(const struct efi_memory_desc *md)
+{
+	return efi_virt_to_phys(md->virt_start) - md->phys_start;
+}
+
 #endif
diff --git a/include/efi/services.h b/include/efi/services.h
index 2d7167b25205..83dc56150a4e 100644
--- a/include/efi/services.h
+++ b/include/efi/services.h
@@ -162,6 +162,8 @@ enum efi_reset_type {
 #define EFI_RUNTIME_SERVICES_SIGNATURE ((u64)0x56524553544e5552ULL)
 #define EFI_RUNTIME_SERVICES_REVISION  0x00010000
 
+#define EFI_OPTIONAL_PTR	0x00000001
+
 struct efi_capsule_header;
 
 struct efi_runtime_services {
-- 
2.47.3