[PATCH v2 5/6] efi: xen: Implement memory descriptor lookup based on hypercall

[Ard Biesheuvel <ardb@kernel.org>]

Xen on x86 boots dom0 in EFI mode but without providing a memory map.
This means that some sanity checks we would like to perform on
configuration tables or other data structures in memory are not
currently possible. Xen does, however, expose EFI memory descriptor info
via a Xen hypercall, so let's wire that up instead.

Co-developed-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Demi Marie Obenour <demi@invisiblethingslab.com>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
---
 drivers/firmware/efi/efi.c |  5 ++-
 drivers/xen/efi.c          | 34 ++++++++++++++++++++
 include/linux/efi.h        |  1 +
 3 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
index 55bd3f4aab28..2c12b1a06481 100644
--- a/drivers/firmware/efi/efi.c
+++ b/drivers/firmware/efi/efi.c
@@ -456,7 +456,7 @@ void __init efi_find_mirror(void)
  * and if so, populate the supplied memory descriptor with the appropriate
  * data.
  */
-int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
+int __efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
 {
 	efi_memory_desc_t *md;
 
@@ -485,6 +485,9 @@ int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
 	return -ENOENT;
 }
 
+extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
+	 __weak __alias(__efi_mem_desc_lookup);
+
 /*
  * Calculate the highest address of an efi memory descriptor.
  */
diff --git a/drivers/xen/efi.c b/drivers/xen/efi.c
index d1ff2186ebb4..74f3f6d8cdc8 100644
--- a/drivers/xen/efi.c
+++ b/drivers/xen/efi.c
@@ -26,6 +26,7 @@
 
 #include <xen/interface/xen.h>
 #include <xen/interface/platform.h>
+#include <xen/page.h>
 #include <xen/xen.h>
 #include <xen/xen-ops.h>
 
@@ -292,3 +293,36 @@ void __init xen_efi_runtime_setup(void)
 	efi.get_next_high_mono_count	= xen_efi_get_next_high_mono_count;
 	efi.reset_system		= xen_efi_reset_system;
 }
+
+int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md)
+{
+	static_assert(XEN_PAGE_SHIFT == EFI_PAGE_SHIFT,
+		      "Mismatch between EFI_PAGE_SHIFT and XEN_PAGE_SHIFT");
+	struct xen_platform_op op = {
+		.cmd = XENPF_firmware_info,
+		.u.firmware_info = {
+			.type = XEN_FW_EFI_INFO,
+			.index = XEN_FW_EFI_MEM_INFO,
+			.u.efi_info.mem.addr = phys_addr,
+			.u.efi_info.mem.size = U64_MAX - phys_addr,
+		}
+	};
+	union xenpf_efi_info *info = &op.u.firmware_info.u.efi_info;
+	int rc;
+
+	if (!efi_enabled(EFI_PARAVIRT) || efi_enabled(EFI_MEMMAP))
+		return __efi_mem_desc_lookup(phys_addr, out_md);
+
+	rc = HYPERVISOR_platform_op(&op);
+	if (rc) {
+		pr_warn("Failed to lookup header 0x%llx in Xen memory map: error %d\n",
+			phys_addr, rc);
+	}
+
+	out_md->phys_addr	= info->mem.addr;
+	out_md->num_pages	= info->mem.size >> EFI_PAGE_SHIFT;
+	out_md->type		= info->mem.type;
+	out_md->attribute	= info->mem.attr;
+
+        return 0;
+}
diff --git a/include/linux/efi.h b/include/linux/efi.h
index 256e70e42114..e0ee6f6da4b4 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -731,6 +731,7 @@ extern u64 efi_mem_attribute (unsigned long phys_addr, unsigned long size);
 extern int __init efi_uart_console_only (void);
 extern u64 efi_mem_desc_end(efi_memory_desc_t *md);
 extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
+extern int __efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
 extern void efi_mem_reserve(phys_addr_t addr, u64 size);
 extern int efi_mem_reserve_persistent(phys_addr_t addr, u64 size);
 extern void efi_initialize_iomem_resources(struct resource *code_resource,
-- 
2.35.1