linux-kernel - [PATCH 12/13] efi: Fix efi_memmap

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Date:   Mon, 13 Jan 2020 18:22:44 +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>, linux-kernel@...r.kernel.org,
        Anshuman Khandual <anshuman.khandual@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Young <dyoung@...hat.com>,
        Saravana Kannan <saravanak@...gle.com>
Subject: [PATCH 12/13] efi: Fix efi_memmap_alloc() leaks

From: Dan Williams <dan.j.williams@...el.com>

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=.

[ ardb: added a comment to clarify that efi_memmap_free() does nothing when
        called from efi_clean_memmap(), i.e., with data->flags == 0x0 ]

Signed-off-by: Dan Williams <dan.j.williams@...el.com>
Signed-off-by: Ard Biesheuvel <ardb@...nel.org>
---
 drivers/firmware/efi/memmap.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/firmware/efi/memmap.c b/drivers/firmware/efi/memmap.c
index 04dfa56b994b..501672166502 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.
@@ -100,6 +122,9 @@ static int __init __efi_memmap_init(struct efi_memory_map_data *data)
 		return -ENOMEM;
 	}
 
+	/* NOP if data->flags & (EFI_MEMMAP_MEMBLOCK | EFI_MEMMAP_SLAB) == 0 */
+	efi_memmap_free();
+
 	map.phys_map = data->phys_map;
 	map.nr_map = data->size / data->desc_size;
 	map.map_end = map.map + data->size;
-- 
2.20.1