linux-kernel - [PATCH v3 3/4] efi: Fix efi_memmap

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Date:   Wed, 01 Jan 2020 20:13:33 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     mingo@...hat.com
Cc:     Taku Izumi <izumi.taku@...fujitsu.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
        kexec@...ts.infradead.org, x86@...nel.org
Subject: [PATCH v3 3/4] efi: Fix efi_memmap_alloc() leaks

With efi_fake_memmap() and efi_arch_mem_reserve() the efi table may be
updated and replaced multiple times. When that happens a previous
dynamically allocated efi memory map can be garbage collected. Use the
new EFI_MEMMAP_{SLAB,MEMBLOCK} flags to detect when a dynamically
allocated memory map is being replaced.

Debug statements in efi_memmap_free() reveal:

 efi: __efi_memmap_free:37: phys: 0x23ffdd580 size: 2688 flags: 0x2
 efi: __efi_memmap_free:37: phys: 0x9db00 size: 2640 flags: 0x2
 efi: __efi_memmap_free:37: phys: 0x9e580 size: 2640 flags: 0x2

...a savings of 7968 bytes on a qemu boot with 2 entries specified to
efi_fake_mem=.

Cc: Taku Izumi <izumi.taku@...fujitsu.com>
Cc: Ard Biesheuvel <ard.biesheuvel@...aro.org>
Signed-off-by: Dan Williams <dan.j.williams@...el.com>
---
 drivers/firmware/efi/memmap.c |   24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
index 2b81ee6858a9..46c8b4056cc1 100644
--- a/drivers/firmware/efi/memmap.c
+++ b/drivers/firmware/efi/memmap.c
@@ -29,6 +29,28 @@ static phys_addr_t __init __efi_memmap_alloc_late(unsigned long size)
 	return PFN_PHYS(page_to_pfn(p));
 }
 
+static void __init __efi_memmap_free(u64 phys, unsigned long size, unsigned long flags)
+{
+	if (flags & EFI_MEMMAP_MEMBLOCK) {
+		if (slab_is_available())
+			memblock_free_late(phys, size);
+		else
+			memblock_free(phys, size);
+	} else if (flags & EFI_MEMMAP_SLAB) {
+		struct page *p = pfn_to_page(PHYS_PFN(phys));
+		unsigned int order = get_order(size);
+
+		free_pages((unsigned long) page_address(p), order);
+	}
+}
+
+static void __init efi_memmap_free(void)
+{
+	__efi_memmap_free(efi.memmap.phys_map,
+			efi.memmap.desc_size * efi.memmap.nr_map,
+			efi.memmap.flags);
+}
+
 /**
  * efi_memmap_alloc - Allocate memory for the EFI memory map
  * @num_entries: Number of entries in the allocated map.
@@ -90,6 +112,8 @@ __efi_memmap_init(struct efi_memory_map_data *data, unsigned long flags)
 		return -ENOMEM;
 	}
 
+	efi_memmap_free();
+
 	map.phys_map = data->phys_map;
 	map.nr_map = data->size / data->desc_size;
 	map.map_end = map.map + data->size;