efi/x86: Don't panic or BUG() on non-critical error conditions

The logic in __efi_enter_virtual_mode() does a number of steps in
sequence, all of which may fail in one way or the other. In most
cases, we simply print an error and disable EFI runtime services
support, but in some cases, we BUG() or panic() and bring down the
system when encountering conditions that we could easily handle in
the same way.

While at it, replace a pointless page-to-virt-phys conversion with
one that goes straight from struct page to physical.

Signed-off-by: Ard Biesheuvel <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Arvind Sankar <[email protected]>
Cc: Matthew Garrett <[email protected]>
Cc: [email protected]
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>

Author: ardbiesheuvel

arch/x86/platform/efi/efi.c

@@ -889,16 +889,14 @@ static void __init __efi_enter_virtual_mode(void)
 
 	if (efi_alloc_page_tables()) {
 		pr_err("Failed to allocate EFI page tables\n");
-		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
-		return;
+		goto err;
 	}
 
 	efi_merge_regions();
 	new_memmap = efi_map_regions(&count, &pg_shift);
 	if (!new_memmap) {
 		pr_err("Error reallocating memory, EFI runtime non-functional!\n");
-		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
-		return;
+		goto err;
 	}
 
 	pa = __pa(new_memmap);
@@ -912,21 +910,19 @@ static void __init __efi_enter_virtual_mode(void)
 
 	if (efi_memmap_init_late(pa, efi.memmap.desc_size * count)) {
 		pr_err("Failed to remap late EFI memory map\n");
-		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
-		return;
+		goto err;
 	}
 
 	if (efi_enabled(EFI_DBG)) {
 		pr_info("EFI runtime memory map:\n");
 		efi_print_memmap();
 	}
 
-	BUG_ON(!efi.systab);
+	if (WARN_ON(!efi.systab))
+		goto err;
 
-	if (efi_setup_page_tables(pa, 1 << pg_shift)) {
-		clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
-		return;
-	}
+	if (efi_setup_page_tables(pa, 1 << pg_shift))
+		goto err;
 
 	efi_sync_low_kernel_mappings();
 
@@ -935,9 +931,9 @@ static void __init __efi_enter_virtual_mode(void)
 					     efi.memmap.desc_version,
 					     (efi_memory_desc_t *)pa);
 	if (status != EFI_SUCCESS) {
-		pr_alert("Unable to switch EFI into virtual mode (status=%lx)!\n",
-			 status);
-		panic("EFI call to SetVirtualAddressMap() failed!");
+		pr_err("Unable to switch EFI into virtual mode (status=%lx)!\n",
+		       status);
+		goto err;
 	}
 
 	efi_free_boot_services();
@@ -964,6 +960,10 @@ static void __init __efi_enter_virtual_mode(void)
 
 	/* clean DUMMY object */
 	efi_delete_dummy_variable();
+	return;
+
+err:
+	clear_bit(EFI_RUNTIME_SERVICES, &efi.flags);
 }
 
 void __init efi_enter_virtual_mode(void)

arch/x86/platform/efi/efi_64.c

@@ -384,11 +384,12 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
 		return 0;
 
 	page = alloc_page(GFP_KERNEL|__GFP_DMA32);
-	if (!page)
-		panic("Unable to allocate EFI runtime stack < 4GB\n");
+	if (!page) {
+		pr_err("Unable to allocate EFI runtime stack < 4GB\n");
+		return 1;
+	}
 
-	efi_scratch.phys_stack = virt_to_phys(page_address(page));
-	efi_scratch.phys_stack += PAGE_SIZE; /* stack grows down */
+	efi_scratch.phys_stack = page_to_phys(page + 1); /* stack grows down */
 
 	npages = (_etext - _text) >> PAGE_SHIFT;
 	text = __pa(_text);