kernel/linux.git/drivers/firmware/efi/libstub/randomalloc.c, branch v6.12.80

efi/libstub: Avoid physical address 0x0 when doing random allocation

2025-03-28T21:03:30+00:00

commit cb16dfed0093217a68c0faa9394fa5823927e04c upstream. Ben reports spurious EFI zboot failures on a system where physical RAM starts at 0x0. When doing random memory allocation from the EFI stub on such a platform, a random seed of 0x0 (which means no entropy source is available) will result in the allocation to be placed at address 0x0 if sufficient space is available. When this allocation is subsequently passed on to the decompression code, the 0x0 address is mistaken for NULL and the code complains and gives up. So avoid address 0x0 when doing random allocation, and set the minimum address to the minimum alignment. Cc: Reported-by: Ben Schneider Tested-by: Ben Schneider Reviewed-by: Ilias Apalodimas Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman

efi: Avoid cold plugged memory for placing the kernel

2025-02-21T13:01:34+00:00

commit ba69e0750b0362870294adab09339a0c39c3beaf upstream. UEFI 2.11 introduced EFI_MEMORY_HOT_PLUGGABLE to annotate system memory regions that are 'cold plugged' at boot, i.e., hot pluggable memory that is available from early boot, and described as system RAM by the firmware. Existing loaders and EFI applications running in the boot context will happily use this memory for allocating data structures that cannot be freed or moved at runtime, and this prevents the memory from being unplugged. Going forward, the new EFI_MEMORY_HOT_PLUGGABLE attribute should be tested, and memory annotated as such should be avoided for such allocations. In the EFI stub, there are a couple of occurrences where, instead of the high-level AllocatePages() UEFI boot service, a low-level code sequence is used that traverses the EFI memory map and carves out the requested number of pages from a free region. This is needed, e.g., for allocating as low as possible, or for allocating pages at random. While AllocatePages() should presumably avoid special purpose memory and cold plugged regions, this manual approach needs to incorporate this logic itself, in order to prevent the kernel itself from ending up in a hot unpluggable region, preventing it from being unplugged. So add the EFI_MEMORY_HOTPLUGGABLE macro definition, and check for it where appropriate. Cc: stable@vger.kernel.org Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman

efi/libstub: Cast away type warning in use of max()

2024-03-28T15:18:57+00:00

Avoid a type mismatch warning in max() by switching to max_t() and providing the type explicitly. Fixes: 3cb4a4827596abc82e ("efi/libstub: fix efi_random_alloc() ...") Signed-off-by: Ard Biesheuvel

efi/libstub: fix efi_random_alloc() to allocate memory at alloc_min or higher address

2024-03-22T13:08:42+00:00

Following warning is sometimes observed while booting my servers: [ 3.594838] DMA: preallocated 4096 KiB GFP_KERNEL pool for atomic allocations [ 3.602918] swapper/0: page allocation failure: order:10, mode:0xcc1(GFP_KERNEL|GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0-1 ... [ 3.851862] DMA: preallocated 1024 KiB GFP_KERNEL|GFP_DMA pool for atomic allocation If 'nokaslr' boot option is set, the warning always happens. On x86, ZONE_DMA is small zone at the first 16MB of physical address space. When this problem happens, most of that space seems to be used by decompressed kernel. Thereby, there is not enough space at DMA_ZONE to meet the request of DMA pool allocation. The commit 2f77465b05b1 ("x86/efistub: Avoid placing the kernel below LOAD_PHYSICAL_ADDR") tried to fix this problem by introducing lower bound of allocation. But the fix is not complete. efi_random_alloc() allocates pages by following steps. 1. Count total available slots ('total_slots') 2. Select a slot ('target_slot') to allocate randomly 3. Calculate a starting address ('target') to be included target_slot 4. Allocate pages, which starting address is 'target' In step 1, 'alloc_min' is used to offset the starting address of memory chunk. But in step 3 'alloc_min' is not considered at all. As the result, 'target' can be miscalculated and become lower than 'alloc_min'. When KASLR is disabled, 'target_slot' is always 0 and the problem happens everytime if the EFI memory map of the system meets the condition. Fix this problem by calculating 'target' considering 'alloc_min'. Cc: linux-efi@vger.kernel.org Cc: Tom Englund Cc: linux-kernel@vger.kernel.org Fixes: 2f77465b05b1 ("x86/efistub: Avoid placing the kernel below LOAD_PHYSICAL_ADDR") Signed-off-by: Kazuma Kondo Signed-off-by: Ard Biesheuvel

x86/efistub: Avoid placing the kernel below LOAD_PHYSICAL_ADDR

2024-01-30T20:44:21+00:00

The EFI stub's kernel placement logic randomizes the physical placement of the kernel by taking all available memory into account, and picking a region at random, based on a random seed. When KASLR is disabled, this seed is set to 0x0, and this results in the lowest available region of memory to be selected for loading the kernel, even if this is below LOAD_PHYSICAL_ADDR. Some of this memory is typically reserved for the GFP_DMA region, to accommodate masters that can only access the first 16 MiB of system memory. Even if such devices are rare these days, we may still end up with a warning in the kernel log, as reported by Tom: swapper/0: page allocation failure: order:10, mode:0xcc1(GFP_KERNEL|GFP_DMA), nodemask=(null),cpuset=/,mems_allowed=0 Fix this by tweaking the random allocation logic to accept a low bound on the placement, and set it to LOAD_PHYSICAL_ADDR. Fixes: a1b87d54f4e4 ("x86/efistub: Avoid legacy decompressor when doing EFI boot") Reported-by: Tom Englund Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218404 Signed-off-by: Ard Biesheuvel

efi/libstub: Add limit argument to efi_random_alloc()

2023-08-07T19:01:46+00:00

x86 will need to limit the kernel memory allocation to the lowest 512 MiB of memory, to match the behavior of the existing bare metal KASLR physical randomization logic. So in preparation for that, add a limit parameter to efi_random_alloc() and wire it up. Signed-off-by: Ard Biesheuvel Signed-off-by: Borislav Petkov (AMD) Link: https://lore.kernel.org/r/20230807162720.545787-22-ardb@kernel.org

efi/libstub: randomalloc: Return EFI_OUT_OF_RESOURCES on failure

2023-03-23T14:15:45+00:00

The logic in efi_random_alloc() will iterate over the memory map twice, once to count the number of candidate slots, and another time to locate the chosen slot after randomization. If there is insufficient memory to do the allocation, the second loop will run to completion without actually having located a slot, but we currently return EFI_SUCCESS in this case, as we fail to initialize status to the appropriate error value of EFI_OUT_OF_RESOURCES. Signed-off-by: Ard Biesheuvel

arm64: efi: Limit allocations to 48-bit addressable physical region

2022-12-07T18:50:44+00:00

The UEFI spec does not mention or reason about the configured size of the virtual address space at all, but it does mention that all memory should be identity mapped using a page size of 4 KiB. This means that a LPA2 capable system that has any system memory outside of the 48-bit addressable physical range and follows the spec to the letter may serve page allocation requests from regions of memory that the kernel cannot access unless it was built with LPA2 support and enables it at runtime. So let's ensure that all page allocations are limited to the 48-bit range. Signed-off-by: Ard Biesheuvel

efi: libstub: use EFI_LOADER_CODE region when moving the kernel in memory

2022-11-18T08:14:08+00:00

The EFI spec is not very clear about which permissions are being given when allocating pages of a certain type. However, it is quite obvious that EFI_LOADER_CODE is more likely to permit execution than EFI_LOADER_DATA, which becomes relevant once we permit booting the kernel proper with the firmware's 1:1 mapping still active. Ostensibly, recent systems such as the Surface Pro X grant executable permissions to EFI_LOADER_CODE regions but not EFI_LOADER_DATA regions. Signed-off-by: Ard Biesheuvel

efi: libstub: install boot-time memory map as config table

2022-09-27T11:22:49+00:00

Expose the EFI boot time memory map to the kernel via a configuration table. This is arch agnostic and enables future changes that remove the dependency on DT on architectures that don't otherwise rely on it. Signed-off-by: Ard Biesheuvel