kernel/drivers/firmware/efi/libstub/random.c, branch linux-6.9.y

efi: stub: use random seed from EFI variable

2022-12-01T08:51:21Z

EFI has a rather unique benefit that it has access to some limited non-volatile storage, where the kernel can store a random seed. Read that seed in EFISTUB and concatenate it with other seeds we wind up passing onward to the kernel in the configuration table. This is complementary to the current other two sources - previous bootloaders, and the EFI RNG protocol. Signed-off-by: Jason A. Donenfeld [ardb: check for non-NULL RNG protocol pointer, call GetVariable() without buffer first to obtain the size] Signed-off-by: Ard Biesheuvel

efi: random: combine bootloader provided RNG seed with RNG protocol output

2022-11-18T09:19:55Z

Instead of blindly creating the EFI random seed configuration table if the RNG protocol is implemented and works, check whether such a EFI configuration table was provided by an earlier boot stage and if so, concatenate the existing and the new seeds, leaving it up to the core code to mix it in and credit it the way it sees fit. This can be used for, e.g., systemd-boot, to pass an additional seed to Linux in a way that can be consumed by the kernel very early. In that case, the following definitions should be used to pass the seed to the EFI stub: struct linux_efi_random_seed { u32 size; // of the 'seed' array in bytes u8 seed[]; }; The memory for the struct must be allocated as EFI_ACPI_RECLAIM_MEMORY pool memory, and the address of the struct in memory should be installed as a EFI configuration table using the following GUID: LINUX_EFI_RANDOM_SEED_TABLE_GUID 1ce1e5bc-7ceb-42f2-81e5-8aadf180f57b Note that doing so is safe even on kernels that were built without this patch applied, but the seed will simply be overwritten with a seed derived from the EFI RNG protocol, if available. The recommended seed size is 32 bytes, and seeds larger than 512 bytes are considered corrupted and ignored entirely. In order to preserve forward secrecy, seeds from previous bootloaders are memzero'd out, and in order to preserve memory, those older seeds are also freed from memory. Freeing from memory without first memzeroing is not safe to do, as it's possible that nothing else will ever overwrite those pages used by EFI. Reviewed-by: Jason A. Donenfeld [ardb: incorporate Jason's followup changes to extend the maximum seed size on the consumer end, memzero() it and drop a needless printk] Signed-off-by: Ard Biesheuvel

efi: random: Use 'ACPI reclaim' memory for random seed

2022-10-24T08:23:28Z

EFI runtime services data is guaranteed to be preserved by the OS, making it a suitable candidate for the EFI random seed table, which may be passed to kexec kernels as well (after refreshing the seed), and so we need to ensure that the memory is preserved without support from the OS itself. However, runtime services data is intended for allocations that are relevant to the implementations of the runtime services themselves, and so they are unmapped from the kernel linear map, and mapped into the EFI page tables that are active while runtime service invocations are in progress. None of this is needed for the RNG seed. So let's switch to EFI 'ACPI reclaim' memory: in spite of the name, there is nothing exclusively ACPI about it, it is simply a type of allocation that carries firmware provided data which may or may not be relevant to the OS, and it is left up to the OS to decide whether to reclaim it after having consumed its contents. Given that in Linux, we never reclaim these allocations, it is a good choice for the EFI RNG seed, as the allocation is guaranteed to survive kexec reboots. One additional reason for changing this now is to align it with the upcoming recommendation for EFI bootloader provided RNG seeds, which must not use EFI runtime services code/data allocations. Cc: # v4.14+ Signed-off-by: Ard Biesheuvel Reviewed-by: Ilias Apalodimas

efi/libstub: Describe RNG functions

2020-02-23T20:57:19Z

Provide descriptions for the functions invoking the EFI_RNG_PROTOCOL. Signed-off-by: Heinrich Schuchardt Reviewed-by: Dominik Brodowski Link: https://lore.kernel.org/r/20200221114716.4372-1-xypron.glpk@gmx.de Signed-off-by: Ard Biesheuvel

efi/libstub: Move efi_random_alloc() into separate source file

2020-02-23T20:57:15Z

efi_random_alloc() is only used on arm64, but as it shares a source file with efi_random_get_seed(), the latter will pull in the former on other architectures as well. Let's take advantage of the fact that libstub is a static library, and so the linker will only incorporate objects that are needed to satisfy dependencies in other objects. This means we can move the random alloc code to a separate source file that gets built unconditionally, but only used when needed. Signed-off-by: Ard Biesheuvel

efi/libstub: Rename efi_call_early/_runtime macros to be more intuitive

2019-12-25T09:49:25Z

The macros efi_call_early and efi_call_runtime are used to call EFI boot services and runtime services, respectively. However, the naming is confusing, given that the early vs runtime distinction may suggest that these are used for calling the same set of services either early or late (== at runtime), while in reality, the sets of services they can be used with are completely disjoint, and efi_call_runtime is also only usable in 'early' code. So do a global sweep to replace all occurrences with efi_bs_call or efi_rt_call, respectively, where BS and RT match the idiom used by the UEFI spec to refer to boot time or runtime services. While at it, use 'func' as the macro parameter name for the function pointers, which is less likely to collide and cause weird build errors. Signed-off-by: Ard Biesheuvel Cc: Arvind Sankar Cc: Borislav Petkov Cc: James Morse Cc: Matt Fleming Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191224151025.32482-24-ardb@kernel.org Signed-off-by: Ingo Molnar

efi/libstub: Drop protocol argument from efi_call_proto() macro

2019-12-25T09:49:24Z

After refactoring the mixed mode support code, efi_call_proto() no longer uses its protocol argument in any of its implementation, so let's remove it altogether. Signed-off-by: Ard Biesheuvel Cc: Arvind Sankar Cc: Borislav Petkov Cc: James Morse Cc: Matt Fleming Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191224151025.32482-22-ardb@kernel.org Signed-off-by: Ingo Molnar

efi/libstub: Remove 'sys_table_arg' from all function prototypes

2019-12-25T09:49:23Z

We have a helper efi_system_table() that gives us the address of the EFI system table in memory, so there is no longer point in passing it around from each function to the next. Signed-off-by: Ard Biesheuvel Cc: Arvind Sankar Cc: Borislav Petkov Cc: James Morse Cc: Matt Fleming Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191224151025.32482-20-ardb@kernel.org Signed-off-by: Ingo Molnar

efi/libstub: Annotate firmware routines as __efiapi

2019-12-25T09:49:19Z

Annotate all the firmware routines (boot services, runtime services and protocol methods) called in the boot context as __efiapi, and make it expand to __attribute__((ms_abi)) on 64-bit x86. This allows us to use the compiler to generate the calls into firmware that use the MS calling convention instead of the SysV one. Signed-off-by: Ard Biesheuvel Cc: Arvind Sankar Cc: Borislav Petkov Cc: James Morse Cc: Matt Fleming Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191224151025.32482-13-ardb@kernel.org Signed-off-by: Ingo Molnar

efi/libstub: Drop explicit 32/64-bit protocol definitions

2019-12-25T09:49:18Z

Now that we have incorporated the mixed mode protocol definitions into the native ones using unions, we no longer need the separate 32/64 bit struct definitions, with the exception of the EFI system table definition and the boot services, runtime services and configuration table definitions. So drop the unused ones. Signed-off-by: Ard Biesheuvel Cc: Arvind Sankar Cc: Borislav Petkov Cc: James Morse Cc: Matt Fleming Cc: Thomas Gleixner Cc: linux-efi@vger.kernel.org Link: https://lkml.kernel.org/r/20191224151025.32482-11-ardb@kernel.org Signed-off-by: Ingo Molnar