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The archrandom interface was originally designed for x86, which supplies RDRAND/RDSEED for receiving random words into registers, resulting in one function to generate an int and another to generate a long. However, other architectures don't follow this. On arm64, the SMCCC TRNG interface can return between one and three longs. On s390, the CPACF TRNG interface can return arbitrary amounts, with four longs having the same cost as one. On UML, the os_getrandom() interface can return arbitrary amounts. So change the api signature to take a "max_longs" parameter designating the maximum number of longs requested, and then return the number of longs generated. Since callers need to check this return value and loop anyway, each arch implementation does not bother implementing its own loop to try again to fill the maximum number of longs. Additionally, all existing callers pass in a constant max_longs parameter. Taken together, these two things mean that the codegen doesn't really change much for one-word-at-a-time platforms, while performance is greatly improved on platforms such as s390. Acked-by: Heiko Carstens <hca@linux.ibm.com> Acked-by: Catalin Marinas <catalin.marinas@arm.com> Acked-by: Mark Rutland <mark.rutland@arm.com> Acked-by: Michael Ellerman <mpe@ellerman.id.au> Acked-by: Borislav Petkov <bp@suse.de> Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
94 lines
2.7 KiB
C
94 lines
2.7 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright (C) 2016 Linaro Ltd <ard.biesheuvel@linaro.org>
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*/
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#include <linux/cache.h>
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#include <linux/crc32.h>
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#include <linux/init.h>
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#include <linux/libfdt.h>
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#include <linux/mm_types.h>
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#include <linux/sched.h>
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#include <linux/types.h>
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#include <linux/pgtable.h>
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#include <linux/random.h>
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#include <asm/fixmap.h>
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#include <asm/kernel-pgtable.h>
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#include <asm/memory.h>
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#include <asm/mmu.h>
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#include <asm/sections.h>
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#include <asm/setup.h>
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u64 __ro_after_init module_alloc_base;
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u16 __initdata memstart_offset_seed;
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struct arm64_ftr_override kaslr_feature_override __initdata;
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static int __init kaslr_init(void)
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{
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u64 module_range;
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u32 seed;
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/*
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* Set a reasonable default for module_alloc_base in case
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* we end up running with module randomization disabled.
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*/
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module_alloc_base = (u64)_etext - MODULES_VSIZE;
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if (kaslr_feature_override.val & kaslr_feature_override.mask & 0xf) {
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pr_info("KASLR disabled on command line\n");
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return 0;
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}
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if (!kaslr_offset()) {
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pr_warn("KASLR disabled due to lack of seed\n");
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return 0;
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}
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pr_info("KASLR enabled\n");
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/*
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* KASAN without KASAN_VMALLOC does not expect the module region to
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* intersect the vmalloc region, since shadow memory is allocated for
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* each module at load time, whereas the vmalloc region will already be
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* shadowed by KASAN zero pages.
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*/
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BUILD_BUG_ON((IS_ENABLED(CONFIG_KASAN_GENERIC) ||
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IS_ENABLED(CONFIG_KASAN_SW_TAGS)) &&
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!IS_ENABLED(CONFIG_KASAN_VMALLOC));
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seed = get_random_u32();
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if (IS_ENABLED(CONFIG_RANDOMIZE_MODULE_REGION_FULL)) {
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/*
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* Randomize the module region over a 2 GB window covering the
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* kernel. This reduces the risk of modules leaking information
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* about the address of the kernel itself, but results in
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* branches between modules and the core kernel that are
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* resolved via PLTs. (Branches between modules will be
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* resolved normally.)
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*/
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module_range = SZ_2G - (u64)(_end - _stext);
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module_alloc_base = max((u64)_end - SZ_2G, (u64)MODULES_VADDR);
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} else {
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/*
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* Randomize the module region by setting module_alloc_base to
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* a PAGE_SIZE multiple in the range [_etext - MODULES_VSIZE,
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* _stext) . This guarantees that the resulting region still
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* covers [_stext, _etext], and that all relative branches can
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* be resolved without veneers unless this region is exhausted
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* and we fall back to a larger 2GB window in module_alloc()
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* when ARM64_MODULE_PLTS is enabled.
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*/
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module_range = MODULES_VSIZE - (u64)(_etext - _stext);
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}
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/* use the lower 21 bits to randomize the base of the module region */
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module_alloc_base += (module_range * (seed & ((1 << 21) - 1))) >> 21;
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module_alloc_base &= PAGE_MASK;
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return 0;
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}
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subsys_initcall(kaslr_init)
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