1 files changed, 203 insertions, 0 deletions
diff --git a/arch/s390/boot/kaslr.c b/arch/s390/boot/kaslr.c
new file mode 100644
index 000000000..58a8d8c8a
--- /dev/null
+++ b/arch/s390/boot/kaslr.c
@@ -0,0 +1,203 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright IBM Corp. 2019
+ */
+#include <linux/pgtable.h>
+#include <asm/mem_detect.h>
+#include <asm/cpacf.h>
+#include <asm/timex.h>
+#include <asm/sclp.h>
+#include <asm/kasan.h>
+#include "decompressor.h"
+#include "boot.h"
+
+#define PRNG_MODE_TDES	 1
+#define PRNG_MODE_SHA512 2
+#define PRNG_MODE_TRNG	 3
+
+struct prno_parm {
+	u32 res;
+	u32 reseed_counter;
+	u64 stream_bytes;
+	u8  V[112];
+	u8  C[112];
+};
+
+struct prng_parm {
+	u8  parm_block[32];
+	u32 reseed_counter;
+	u64 byte_counter;
+};
+
+static int check_prng(void)
+{
+	if (!cpacf_query_func(CPACF_KMC, CPACF_KMC_PRNG)) {
+		sclp_early_printk("KASLR disabled: CPU has no PRNG\n");
+		return 0;
+	}
+	if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_TRNG))
+		return PRNG_MODE_TRNG;
+	if (cpacf_query_func(CPACF_PRNO, CPACF_PRNO_SHA512_DRNG_GEN))
+		return PRNG_MODE_SHA512;
+	else
+		return PRNG_MODE_TDES;
+}
+
+static int get_random(unsigned long limit, unsigned long *value)
+{
+	struct prng_parm prng = {
+		/* initial parameter block for tdes mode, copied from libica */
+		.parm_block = {
+			0x0F, 0x2B, 0x8E, 0x63, 0x8C, 0x8E, 0xD2, 0x52,
+			0x64, 0xB7, 0xA0, 0x7B, 0x75, 0x28, 0xB8, 0xF4,
+			0x75, 0x5F, 0xD2, 0xA6, 0x8D, 0x97, 0x11, 0xFF,
+			0x49, 0xD8, 0x23, 0xF3, 0x7E, 0x21, 0xEC, 0xA0
+		},
+	};
+	unsigned long seed, random;
+	struct prno_parm prno;
+	__u64 entropy[4];
+	int mode, i;
+
+	mode = check_prng();
+	seed = get_tod_clock_fast();
+	switch (mode) {
+	case PRNG_MODE_TRNG:
+		cpacf_trng(NULL, 0, (u8 *) &random, sizeof(random));
+		break;
+	case PRNG_MODE_SHA512:
+		cpacf_prno(CPACF_PRNO_SHA512_DRNG_SEED, &prno, NULL, 0,
+			   (u8 *) &seed, sizeof(seed));
+		cpacf_prno(CPACF_PRNO_SHA512_DRNG_GEN, &prno, (u8 *) &random,
+			   sizeof(random), NULL, 0);
+		break;
+	case PRNG_MODE_TDES:
+		/* add entropy */
+		*(unsigned long *) prng.parm_block ^= seed;
+		for (i = 0; i < 16; i++) {
+			cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block,
+				  (u8 *) entropy, (u8 *) entropy,
+				  sizeof(entropy));
+			memcpy(prng.parm_block, entropy, sizeof(entropy));
+		}
+		random = seed;
+		cpacf_kmc(CPACF_KMC_PRNG, prng.parm_block, (u8 *) &random,
+			  (u8 *) &random, sizeof(random));
+		break;
+	default:
+		return -1;
+	}
+	*value = random % limit;
+	return 0;
+}
+
+/*
+ * To randomize kernel base address we have to consider several facts:
+ * 1. physical online memory might not be continuous and have holes. mem_detect
+ *    info contains list of online memory ranges we should consider.
+ * 2. we have several memory regions which are occupied and we should not
+ *    overlap and destroy them. Currently safe_addr tells us the border below
+ *    which all those occupied regions are. We are safe to use anything above
+ *    safe_addr.
+ * 3. the upper limit might apply as well, even if memory above that limit is
+ *    online. Currently those limitations are:
+ *    3.1. Limit set by "mem=" kernel command line option
+ *    3.2. memory reserved at the end for kasan initialization.
+ * 4. kernel base address must be aligned to THREAD_SIZE (kernel stack size).
+ *    Which is required for CONFIG_CHECK_STACK. Currently THREAD_SIZE is 4 pages
+ *    (16 pages when the kernel is built with kasan enabled)
+ * Assumptions:
+ * 1. kernel size (including .bss size) and upper memory limit are page aligned.
+ * 2. mem_detect memory region start is THREAD_SIZE aligned / end is PAGE_SIZE
+ *    aligned (in practice memory configurations granularity on z/VM and LPAR
+ *    is 1mb).
+ *
+ * To guarantee uniform distribution of kernel base address among all suitable
+ * addresses we generate random value just once. For that we need to build a
+ * continuous range in which every value would be suitable. We can build this
+ * range by simply counting all suitable addresses (let's call them positions)
+ * which would be valid as kernel base address. To count positions we iterate
+ * over online memory ranges. For each range which is big enough for the
+ * kernel image we count all suitable addresses we can put the kernel image at
+ * that is
+ * (end - start - kernel_size) / THREAD_SIZE + 1
+ * Two functions count_valid_kernel_positions and position_to_address help
+ * to count positions in memory range given and then convert position back
+ * to address.
+ */
+static unsigned long count_valid_kernel_positions(unsigned long kernel_size,
+						  unsigned long _min,
+						  unsigned long _max)
+{
+	unsigned long start, end, pos = 0;
+	int i;
+
+	for_each_mem_detect_block(i, &start, &end) {
+		if (_min >= end)
+			continue;
+		if (start >= _max)
+			break;
+		start = max(_min, start);
+		end = min(_max, end);
+		if (end - start < kernel_size)
+			continue;
+		pos += (end - start - kernel_size) / THREAD_SIZE + 1;
+	}
+
+	return pos;
+}
+
+static unsigned long position_to_address(unsigned long pos, unsigned long kernel_size,
+				 unsigned long _min, unsigned long _max)
+{
+	unsigned long start, end;
+	int i;
+
+	for_each_mem_detect_block(i, &start, &end) {
+		if (_min >= end)
+			continue;
+		if (start >= _max)
+			break;
+		start = max(_min, start);
+		end = min(_max, end);
+		if (end - start < kernel_size)
+			continue;
+		if ((end - start - kernel_size) / THREAD_SIZE + 1 >= pos)
+			return start + (pos - 1) * THREAD_SIZE;
+		pos -= (end - start - kernel_size) / THREAD_SIZE + 1;
+	}
+
+	return 0;
+}
+
+unsigned long get_random_base(unsigned long safe_addr)
+{
+	unsigned long memory_limit = get_mem_detect_end();
+	unsigned long base_pos, max_pos, kernel_size;
+	int i;
+
+	memory_limit = min(memory_limit, ident_map_size);
+
+	/*
+	 * Avoid putting kernel in the end of physical memory
+	 * which kasan will use for shadow memory and early pgtable
+	 * mapping allocations.
+	 */
+	memory_limit -= kasan_estimate_memory_needs(memory_limit);
+
+	safe_addr = ALIGN(safe_addr, THREAD_SIZE);
+	kernel_size = vmlinux.image_size + vmlinux.bss_size;
+	if (safe_addr + kernel_size > memory_limit)
+		return 0;
+
+	max_pos = count_valid_kernel_positions(kernel_size, safe_addr, memory_limit);
+	if (!max_pos) {
+		sclp_early_printk("KASLR disabled: not enough memory\n");
+		return 0;
+	}
+
+	/* we need a value in the range [1, base_pos] inclusive */
+	if (get_random(max_pos, &base_pos))
+		return 0;
+	return position_to_address(base_pos + 1, kernel_size, safe_addr, memory_limit);
+}