x86/efi: Don't allocate memmap through memblock after mm_init()

With the following commit:

  4bc9f92e64 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")

...  efi_bgrt_init() calls into the memblock allocator through
efi_mem_reserve() => efi_arch_mem_reserve() *after* mm_init() has been called.

Indeed, KASAN reports a bad read access later on in efi_free_boot_services():

  BUG: KASAN: use-after-free in efi_free_boot_services+0xae/0x24c
            at addr ffff88022de12740
  Read of size 4 by task swapper/0/0
  page:ffffea0008b78480 count:0 mapcount:-127
  mapping:          (null) index:0x1 flags: 0x5fff8000000000()
  [...]
  Call Trace:
   dump_stack+0x68/0x9f
   kasan_report_error+0x4c8/0x500
   kasan_report+0x58/0x60
   __asan_load4+0x61/0x80
   efi_free_boot_services+0xae/0x24c
   start_kernel+0x527/0x562
   x86_64_start_reservations+0x24/0x26
   x86_64_start_kernel+0x157/0x17a
   start_cpu+0x5/0x14

The instruction at the given address is the first read from the memmap's
memory, i.e. the read of md->type in efi_free_boot_services().

Note that the writes earlier in efi_arch_mem_reserve() don't splat because
they're done through early_memremap()ed addresses.

So, after memblock is gone, allocations should be done through the "normal"
page allocator. Introduce a helper, efi_memmap_alloc() for this. Use
it from efi_arch_mem_reserve(), efi_free_boot_services() and, for the sake
of consistency, from efi_fake_memmap() as well.

Note that for the latter, the memmap allocations cease to be page aligned.
This isn't needed though.

Tested-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: <stable@vger.kernel.org> # v4.9
Cc: Dave Young <dyoung@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matt Fleming <matt@codeblueprint.co.uk>
Cc: Mika Penttilä <mika.penttila@nextfour.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Fixes: 4bc9f92e64 ("x86/efi-bgrt: Use efi_mem_reserve() to avoid copying image data")
Link: http://lkml.kernel.org/r/20170105125130.2815-1-nicstange@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/platform/efi/quirks.c

@@ -214,7 +214,7 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
 
 	new_size = efi.memmap.desc_size * num_entries;
 
-	new_phys = memblock_alloc(new_size, 0);
+	new_phys = efi_memmap_alloc(num_entries);
 	if (!new_phys) {
 		pr_err("Could not allocate boot services memmap\n");
 		return;
@@ -355,7 +355,7 @@ void __init efi_free_boot_services(void)
 	}
 
 	new_size = efi.memmap.desc_size * num_entries;
-	new_phys = memblock_alloc(new_size, 0);
+	new_phys = efi_memmap_alloc(num_entries);
 	if (!new_phys) {
 		pr_err("Failed to allocate new EFI memmap\n");
 		return;

drivers/firmware/efi/fake_mem.c

@@ -71,8 +71,7 @@ void __init efi_fake_memmap(void)
 	}
 
 	/* allocate memory for new EFI memmap */
-	new_memmap_phy = memblock_alloc(efi.memmap.desc_size * new_nr_map,
-					PAGE_SIZE);
+	new_memmap_phy = efi_memmap_alloc(new_nr_map);
 	if (!new_memmap_phy)
 		return;
 

drivers/firmware/efi/memmap.c

@@ -9,6 +9,44 @@
 #include <linux/efi.h>
 #include <linux/io.h>
 #include <asm/early_ioremap.h>
+#include <linux/memblock.h>
+#include <linux/slab.h>
+
+static phys_addr_t __init __efi_memmap_alloc_early(unsigned long size)
+{
+	return memblock_alloc(size, 0);
+}
+
+static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
+{
+	unsigned int order = get_order(size);
+	struct page *p = alloc_pages(GFP_KERNEL, order);
+
+	if (!p)
+		return 0;
+
+	return PFN_PHYS(page_to_pfn(p));
+}
+
+/**
+ * efi_memmap_alloc - Allocate memory for the EFI memory map
+ * @num_entries: Number of entries in the allocated map.
+ *
+ * Depending on whether mm_init() has already been invoked or not,
+ * either memblock or "normal" page allocation is used.
+ *
+ * Returns the physical address of the allocated memory map on
+ * success, zero on failure.
+ */
+phys_addr_t __init efi_memmap_alloc(unsigned int num_entries)
+{
+	unsigned long size = num_entries * efi.memmap.desc_size;
+
+	if (slab_is_available())
+		return __efi_memmap_alloc_late(size);
+
+	return __efi_memmap_alloc_early(size);
+}
 
 /**
  * __efi_memmap_init - Common code for mapping the EFI memory map

include/linux/efi.h

@@ -950,6 +950,7 @@ static inline efi_status_t efi_query_variable_store(u32 attributes,
 #endif
 extern void __iomem *efi_lookup_mapped_addr(u64 phys_addr);
 
+extern phys_addr_t __init efi_memmap_alloc(unsigned int num_entries);
 extern int __init efi_memmap_init_early(struct efi_memory_map_data *data);
 extern int __init efi_memmap_init_late(phys_addr_t addr, unsigned long size);
 extern void __init efi_memmap_unmap(void);