210 lines
6.2 KiB
C
210 lines
6.2 KiB
C
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// SPDX-License-Identifier: GPL-2.0
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/*
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* Copyright IBM Corp. 2019
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*/
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#include <linux/pgtable.h>
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#include <asm/mem_detect.h>
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#include <asm/cpacf.h>
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#include <asm/timex.h>
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#include <asm/sclp.h>
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#include <asm/kasan.h>
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#include "compressed/decompressor.h"
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#include "boot.h"
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#define PRNG_MODE_TDES 1
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#define PRNG_MODE_SHA512 2
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#define PRNG_MODE_TRNG 3
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struct prno_parm {
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u32 res;
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u32 reseed_counter;
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u64 stream_bytes;
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u8 V[112];
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u8 C[112];
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};
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struct prng_parm {
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u8 parm_block[32];
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u32 reseed_counter;
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u64 byte_counter;
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};
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static int check_prng(void)
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{
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if (!cpacf_query_func(CPACF_KMC, CPACF_KMC_PRNG)) {
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sclp_early_printk("KASLR disabled: CPU has no PRNG\n");
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return 0;
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}
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if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG))
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return PRNG_MODE_TRNG;
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if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN))
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return PRNG_MODE_SHA512;
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else
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return PRNG_MODE_TDES;
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}
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static int get_random(unsigned long limit, unsigned long *value)
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{
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struct prng_parm prng = {
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/* initial parameter block for tdes mode, copied from libica */
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.parm_block = {
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0x0F, 0x2B, 0x8E, 0x63, 0x8C, 0x8E, 0xD2, 0x52,
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0x64, 0xB7, 0xA0, 0x7B, 0x75, 0x28, 0xB8, 0xF4,
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0x75, 0x5F, 0xD2, 0xA6, 0x8D, 0x97, 0x11, 0xFF,
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0x49, 0xD8, 0x23, 0xF3, 0x7E, 0x21, 0xEC, 0xA0
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},
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};
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unsigned long seed, random;
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struct prno_parm prno;
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__u64 entropy[4];
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int mode, i;
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mode = check_prng();
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seed = get_tod_clock_fast();
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switch (mode) {
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case PRNG_MODE_TRNG:
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cpacf_trng(NULL, 0, (u8 *) &random, sizeof(random));
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break;
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case PRNG_MODE_SHA512:
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cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED, &prno, NULL, 0,
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(u8 *) &seed, sizeof(seed));
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cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN, &prno, (u8 *) &random,
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sizeof(random), NULL, 0);
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break;
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case PRNG_MODE_TDES:
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/* add entropy */
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*(unsigned long *) prng.parm_block ^= seed;
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for (i = 0; i < 16; i++) {
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cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block,
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(u8 *) entropy, (u8 *) entropy,
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sizeof(entropy));
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memcpy(prng.parm_block, entropy, sizeof(entropy));
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}
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random = seed;
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cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block, (u8 *) &random,
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(u8 *) &random, sizeof(random));
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break;
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default:
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return -1;
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}
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*value = random % limit;
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return 0;
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}
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/*
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* To randomize kernel base address we have to consider several facts:
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* 1. physical online memory might not be continuous and have holes. mem_detect
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* info contains list of online memory ranges we should consider.
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* 2. we have several memory regions which are occupied and we should not
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* overlap and destroy them. Currently safe_addr tells us the border below
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* which all those occupied regions are. We are safe to use anything above
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* safe_addr.
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* 3. the upper limit might apply as well, even if memory above that limit is
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* online. Currently those limitations are:
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* 3.1. Limit set by "mem=" kernel command line option
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* 3.2. memory reserved at the end for kasan initialization.
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* 4. kernel base address must be aligned to THREAD_SIZE (kernel stack size).
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* Which is required for CONFIG_CHECK_STACK. Currently THREAD_SIZE is 4 pages
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* (16 pages when the kernel is built with kasan enabled)
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* Assumptions:
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* 1. kernel size (including .bss size) and upper memory limit are page aligned.
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* 2. mem_detect memory region start is THREAD_SIZE aligned / end is PAGE_SIZE
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* aligned (in practice memory configurations granularity on z/VM and LPAR
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* is 1mb).
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*
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* To guarantee uniform distribution of kernel base address among all suitable
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* addresses we generate random value just once. For that we need to build a
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* continuous range in which every value would be suitable. We can build this
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* range by simply counting all suitable addresses (let's call them positions)
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* which would be valid as kernel base address. To count positions we iterate
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* over online memory ranges. For each range which is big enough for the
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* kernel image we count all suitable addresses we can put the kernel image at
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* that is
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* (end - start - kernel_size) / THREAD_SIZE + 1
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* Two functions count_valid_kernel_positions and position_to_address help
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* to count positions in memory range given and then convert position back
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* to address.
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*/
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static unsigned long count_valid_kernel_positions(unsigned long kernel_size,
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unsigned long _min,
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unsigned long _max)
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{
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unsigned long start, end, pos = 0;
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int i;
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for_each_mem_detect_block(i, &start, &end) {
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if (_min >= end)
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continue;
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if (start >= _max)
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break;
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start = max(_min, start);
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end = min(_max, end);
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if (end - start < kernel_size)
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continue;
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pos += (end - start - kernel_size) / THREAD_SIZE + 1;
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}
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return pos;
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}
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static unsigned long position_to_address(unsigned long pos, unsigned long kernel_size,
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unsigned long _min, unsigned long _max)
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{
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unsigned long start, end;
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int i;
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for_each_mem_detect_block(i, &start, &end) {
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if (_min >= end)
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continue;
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if (start >= _max)
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break;
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start = max(_min, start);
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end = min(_max, end);
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if (end - start < kernel_size)
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continue;
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if ((end - start - kernel_size) / THREAD_SIZE + 1 >= pos)
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return start + (pos - 1) * THREAD_SIZE;
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pos -= (end - start - kernel_size) / THREAD_SIZE + 1;
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}
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return 0;
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}
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unsigned long get_random_base(unsigned long safe_addr)
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{
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unsigned long memory_limit = get_mem_detect_end();
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unsigned long base_pos, max_pos, kernel_size;
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unsigned long kasan_needs;
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int i;
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memory_limit = min(memory_limit, ident_map_size);
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/*
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* Avoid putting kernel in the end of physical memory
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* which kasan will use for shadow memory and early pgtable
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* mapping allocations.
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*/
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memory_limit -= kasan_estimate_memory_needs(memory_limit);
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if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_data.start && initrd_data.size) {
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if (safe_addr < initrd_data.start + initrd_data.size)
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safe_addr = initrd_data.start + initrd_data.size;
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}
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safe_addr = ALIGN(safe_addr, THREAD_SIZE);
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kernel_size = vmlinux.image_size + vmlinux.bss_size;
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if (safe_addr + kernel_size > memory_limit)
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return 0;
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max_pos = count_valid_kernel_positions(kernel_size, safe_addr, memory_limit);
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if (!max_pos) {
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sclp_early_printk("KASLR disabled: not enough memory\n");
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return 0;
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}
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/* we need a value in the range [1, base_pos] inclusive */
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if (get_random(max_pos, &base_pos))
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return 0;
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return position_to_address(base_pos + 1, kernel_size, safe_addr, memory_limit);
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}
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