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Subject[PATCH] efi: Fix handling of multiple contiguous efi_fake_mem= entries
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A recent test of efi_fake_mem=4G@9G:0x40000,4G@13G:0x40000 crashed with
a signature of:

BUG: unable to handle page fault for address: ffffffffff281000
[..]
RIP: 0010:efi_memmap_insert+0x11d/0x191
[..]
Call Trace:
? bgrt_init+0xbe/0xbe
? efi_arch_mem_reserve+0x1cb/0x228
? acpi_parse_bgrt+0xa/0xd
? acpi_table_parse+0x86/0xb8
? acpi_boot_init+0x494/0x4e3
? acpi_parse_x2apic+0x87/0x87
? setup_acpi_sci+0xa2/0xa2
? setup_arch+0x8db/0x9e1
? start_kernel+0x6a/0x547
? secondary_startup_64+0xb6/0xc0

efi_memmap_insert() is attempting to insert entries past the end of the
new map. This condition is setup by efi_fake_mem() leaking empty entries
to the end of memory map, and then efi_arch_mem_reserve() trips over the
bad entry when attempting an additional efi_memmap_insert(). The empty
entry causes efi_memmap_insert() to attempt more memmap splits / copies
than efi_memmap_split_count() accounted for when sizing the new map.

Update efi_fake_memmap() to cleanup lagging empty entries.

This change is related to commit af1648984828 "x86/efi: Update e820 with
reserved EFI boot services data to fix kexec breakage" since that
introduces more occurrences where efi_memmap_insert() is invoked after
an efi_fake_mem= configuration has been parsed. Previously the side
effects of vestigial empty entries were benign, but with commit
af1648984828 that follow-on efi_memmap_insert() invocation triggers the
above crash signature.

Fixes: 0f96a99dab36 ("efi: Add 'efi_fake_mem' boot option")
Fixes: af1648984828 ("x86/efi: Update e820 with reserved EFI boot services...")
Cc: Taku Izumi <izumi.taku@jp.fujitsu.com>
Cc: Michael Weiser <michael@weiser.dinsnail.net>
Cc: Dave Young <dyoung@redhat.com>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
drivers/firmware/efi/fake_mem.c | 22 +++++++++++++++++++++-
1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/drivers/firmware/efi/fake_mem.c b/drivers/firmware/efi/fake_mem.c
index bb9fc70d0cfa..6df51ba93ae8 100644
--- a/drivers/firmware/efi/fake_mem.c
+++ b/drivers/firmware/efi/fake_mem.c
@@ -67,13 +67,33 @@ void __init efi_fake_memmap(void)
return;
}

+ memset(new_memmap, 0, efi.memmap.desc_size * new_nr_map);
for (i = 0; i < nr_fake_mem; i++)
efi_memmap_insert(&efi.memmap, new_memmap, &efi_fake_mems[i]);

+ /*
+ * efi_memmap_split_count() may over count the number of
+ * required splits in the case when contiguous fake entries are
+ * specified. Check that all new_nr_map entries were consumed.
+ */
+ for (i = new_nr_map; i > 0; i--) {
+ efi_memory_desc_t *md;
+ u64 start, end;
+
+ md = new_memmap + efi.memmap.desc_size * (new_nr_map - i - 1);
+ end = md->phys_addr + (md->num_pages << EFI_PAGE_SHIFT) - 1;
+ start = md->phys_addr;
+
+ if (start == 0 && end + 1 == 0)
+ continue;
+ break;
+ }
+
/* swap into new EFI memmap */
early_memunmap(new_memmap, efi.memmap.desc_size * new_nr_map);

- efi_memmap_install(new_memmap_phy, new_nr_map);
+ /* install only the valid entries */
+ efi_memmap_install(new_memmap_phy, i);

/* print new EFI memmap */
efi_print_memmap();
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