[PATCH v4 0/4] efi: Fix handling of multiple efi_fake_mem= entries

From: Dan Williams
Date: Mon Jan 06 2020 - 19:56:48 EST

Changes since v3 [1]:
- Rather than pass a reference to a new flags argument, pass a common
data structure ('struct efi_memory_map_data'), between
efi_memmap_alloc() and efi_memmap_install(). (Ard)

- Arrange for EFI_MEMMAP_SLAB to be clear if EFI_MEMMAP_MEMBLOCK was set
and vice versa (Ard).

[1]: http://lore.kernel.org/r/157793839827.977550.7845382457971215205.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

While testing an upcoming patchset to enhance the "soft reservation"
implementation it started crashing when rebased on v5.5-rc3. This
uncovered a few bugs in the efi_fake_mem= handling and
efi_memmap_alloc() leaks.


Copied from patch4:

Dave noticed that when specifying multiple efi_fake_mem= entries only
the last entry was successfully being reflected in the efi memory map.
This is due to the fact that the efi_memmap_insert() is being called
multiple times, but on successive invocations the insertion should be
applied to the last new memmap rather than the original map at
efi_fake_memmap() entry.

Rework efi_fake_memmap() to install the new memory map after each
efi_fake_mem= entry is parsed.

This also fixes an issue in efi_fake_memmap() that caused it to litter
emtpy entries into the end of the efi memory map. An empty entry causes
efi_memmap_insert() to attempt more memmap splits / copies than
efi_memmap_split_count() accounted for when sizing the new map. When
that happens efi_memmap_insert() may overrun its allocation, and if you
are lucky will spill over to an unmapped page leading to crash
signature like the following rather than silent corruption:

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

Commit af1648984828 "x86/efi: Update e820 with reserved EFI boot
services data to fix kexec breakage" is listed in Fixes: since it
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
efi_memmap_insert() overruns.


Dan Williams (4):
efi: Add a flags parameter to efi_memory_map
efi: Add tracking for dynamically allocated memmaps
efi: Fix efi_memmap_alloc() leaks
efi: Fix handling of multiple efi_fake_mem= entries

arch/x86/platform/efi/efi.c | 10 +++-
arch/x86/platform/efi/quirks.c | 23 ++++------
drivers/firmware/efi/fake_mem.c | 43 +++++++++---------
drivers/firmware/efi/memmap.c | 94 ++++++++++++++++++++++++++-------------
include/linux/efi.h | 17 +++++--
5 files changed, 113 insertions(+), 74 deletions(-)