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@@ -130,6 +130,27 @@ efi_status_t efi_query_variable_store(u32 attributes, unsigned long size)
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}
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EXPORT_SYMBOL_GPL(efi_query_variable_store);
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+/*
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+ * Helper function for efi_reserve_boot_services() to figure out if we
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+ * can free regions in efi_free_boot_services().
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+ *
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+ * Use this function to ensure we do not free regions owned by somebody
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+ * else. We must only reserve (and then free) regions:
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+ *
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+ * - Not within any part of the kernel
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+ * - Not the BIOS reserved area (E820_RESERVED, E820_NVS, etc)
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+ */
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+static bool can_free_region(u64 start, u64 size)
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+{
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+ if (start + size > __pa_symbol(_text) && start <= __pa_symbol(_end))
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+ return false;
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+
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+ if (!e820_all_mapped(start, start+size, E820_RAM))
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+ return false;
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+
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+ return true;
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+}
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+
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/*
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* The UEFI specification makes it clear that the operating system is free to do
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* whatever it wants with boot services code after ExitBootServices() has been
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@@ -147,26 +168,50 @@ void __init efi_reserve_boot_services(void)
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efi_memory_desc_t *md = p;
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u64 start = md->phys_addr;
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u64 size = md->num_pages << EFI_PAGE_SHIFT;
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+ bool already_reserved;
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if (md->type != EFI_BOOT_SERVICES_CODE &&
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md->type != EFI_BOOT_SERVICES_DATA)
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continue;
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- /* Only reserve where possible:
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- * - Not within any already allocated areas
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- * - Not over any memory area (really needed, if above?)
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- * - Not within any part of the kernel
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- * - Not the bios reserved area
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- */
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- if ((start + size > __pa_symbol(_text)
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- && start <= __pa_symbol(_end)) ||
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- !e820_all_mapped(start, start+size, E820_RAM) ||
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- memblock_is_region_reserved(start, size)) {
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- /* Could not reserve, skip it */
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- md->num_pages = 0;
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- memblock_dbg("Could not reserve boot range [0x%010llx-0x%010llx]\n",
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- start, start+size-1);
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- } else
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+
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+ already_reserved = memblock_is_region_reserved(start, size);
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+
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+ /*
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+ * Because the following memblock_reserve() is paired
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+ * with free_bootmem_late() for this region in
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+ * efi_free_boot_services(), we must be extremely
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+ * careful not to reserve, and subsequently free,
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+ * critical regions of memory (like the kernel image) or
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+ * those regions that somebody else has already
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+ * reserved.
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+ *
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+ * A good example of a critical region that must not be
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+ * freed is page zero (first 4Kb of memory), which may
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+ * contain boot services code/data but is marked
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+ * E820_RESERVED by trim_bios_range().
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+ */
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+ if (!already_reserved) {
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memblock_reserve(start, size);
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+
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+ /*
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+ * If we are the first to reserve the region, no
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+ * one else cares about it. We own it and can
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+ * free it later.
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+ */
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+ if (can_free_region(start, size))
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+ continue;
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+ }
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+
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+ /*
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+ * We don't own the region. We must not free it.
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+ *
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+ * Setting this bit for a boot services region really
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+ * doesn't make sense as far as the firmware is
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+ * concerned, but it does provide us with a way to tag
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+ * those regions that must not be paired with
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+ * free_bootmem_late().
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+ */
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+ md->attribute |= EFI_MEMORY_RUNTIME;
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}
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}
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@@ -183,8 +228,8 @@ void __init efi_free_boot_services(void)
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md->type != EFI_BOOT_SERVICES_DATA)
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continue;
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- /* Could not reserve boot area */
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- if (!size)
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+ /* Do not free, someone else owns it: */
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+ if (md->attribute & EFI_MEMORY_RUNTIME)
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continue;
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free_bootmem_late(start, size);
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Linus Torvalds