linux-kernel - [PATCH 13/20] efi/x86: don't panic or BUG() on non-critical error conditions

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Date:   Fri,  3 Jan 2020 12:39:46 +0100
From:   Ard Biesheuvel <ardb@...nel.org>
To:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Ard Biesheuvel <ardb@...nel.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, Andy Lutomirski <luto@...nel.org>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Matthew Garrett <mjg59@...gle.com>
Subject: [PATCH 13/20] 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 <ardb@...nel.org>
---
 arch/x86/platform/efi/efi.c    | 28 ++++++++++++++--------------
 arch/x86/platform/efi/efi_64.c |  9 +++++----
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
index 53ed0b123641..4f539bfdc051 100644
--- a/arch/x86/platform/efi/efi.c
+++ b/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);
@@ -912,8 +910,7 @@ 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)) {
@@ -921,12 +918,11 @@ static void __init __efi_enter_virtual_mode(void)
 		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)
diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index 910e9ec03b09..c13fa2150976 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/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);
-- 
2.20.1