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Ard Biesheuvel authored
Our virtual KASLR displacement is a randomly chosen multiple of 2 MiB plus an offset that is equal to the physical placement modulo 2 MiB. This arrangement ensures that we can always use 2 MiB block mappings (or contiguous PTE mappings for 16k or 64k pages) to map the kernel. This means that a KASLR offset of less than 2 MiB is simply the product of this physical displacement, and no randomization has actually taken place. Currently, we use 'kaslr_offset() > 0' to decide whether or not randomization has occurred, and so we misidentify this case. If the kernel image placement is not randomized, modules are allocated from a dedicated region below the kernel mapping, which is only used for modules and not for other vmalloc() or vmap() calls. When randomization is enabled, the kernel image is vmap()'ed randomly inside the vmalloc region, and modules are allocated in the vicinity of this mapping to ensure that relative references are always in range. However, unlike the dedicated module region below the vmalloc region, this region is not reserved exclusively for modules, and so ordinary vmalloc() calls may end up overlapping with it. This should rarely happen, given that vmalloc allocates bottom up, although it cannot be ruled out entirely. The misidentified case results in a placement of the kernel image within 2 MiB of its default address. However, the logic that randomizes the module region is still invoked, and this could result in the module region overlapping with the start of the vmalloc region, instead of using the dedicated region below it. If this happens, a single large vmalloc() or vmap() call will use up the entire region, and leave no space for loading modules after that. Since commit 82046702 ("efi/libstub/arm64: Replace 'preferred' offset with alignment check"), this is much more likely to occur on systems that boot via EFI but lack an implementation of the EFI RNG protocol, as in that case, the EFI stub will decide to leave the image where it found it, and the EFI firmware uses 64k alignment only. Fix this, by correctly identifying the case where the virtual displacement is a result of the physical displacement only. Signed-off-by:
Ard Biesheuvel <ardb@kernel.org> Reviewed-by:
Mark Brown <broonie@kernel.org> Acked-by:
Mark Rutland <mark.rutland@arm.com> Link: https://lore.kernel.org/r/20230223204101.1500373-1-ardb@kernel.orgSigned-off-by:
Catalin Marinas <catalin.marinas@arm.com>
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