s390/boot: rework decompressor reserved tracking

Currently several approaches for finding unused memory in decompressor
are utilized. While "safe_addr" grows towards higher addresses, vmem
code allocates paging structures top down. The former requires careful
ordering. In addition to that ipl report handling code verifies potential
intersections with secure boot certificates on its own. Neither of two
approaches are memory holes aware and consistent with each other in low
memory conditions.

To solve that, existing approaches are generalized and combined
together, as well as online memory ranges are now taken into
consideration.

physmem_info has been extended to contain reserved memory ranges. New
set of functions allow to handle reserves and find unused memory.
All reserves and memory allocations are "typed". In case of out of
memory condition decompressor fails with detailed info on current
reserved ranges and usable online memory.

Linux version 6.2.0 ...
Kernel command line: ... mem=100M
Our of memory allocating 100000 bytes 100000 aligned in range 0:5800000
Reserved memory ranges:
0000000000000000 0000000003e33000 DECOMPRESSOR
0000000003f00000 00000000057648a3 INITRD
00000000063e0000 00000000063e8000 VMEM
00000000063eb000 00000000063f4000 VMEM
00000000063f7800 0000000006400000 VMEM
0000000005800000 0000000006300000 KASAN
Usable online memory ranges (info source: sclp read info [3]):
0000000000000000 0000000006400000
Usable online memory total: 6400000 Reserved: 61b10a3 Free: 24ef5d
Call Trace:
(sp:000000000002bd58 [<0000000000012a70>] physmem_alloc_top_down+0x60/0x14c)
 sp:000000000002bdc8 [<0000000000013756>] _pa+0x56/0x6a
 sp:000000000002bdf0 [<0000000000013bcc>] pgtable_populate+0x45c/0x65e
 sp:000000000002be90 [<00000000000140aa>] setup_vmem+0x2da/0x424
 sp:000000000002bec8 [<0000000000011c20>] startup_kernel+0x428/0x8b4
 sp:000000000002bf60 [<00000000000100f4>] startup_normal+0xd4/0xd4

physmem_alloc_range allows to find free memory in specified range. It
should be used for one time allocations only like finding position for
amode31 and vmlinux.
physmem_alloc_top_down can be used just like physmem_alloc_range, but
it also allows multiple allocations per type and tries to merge sequential
allocations together. Which is useful for paging structures allocations.
If sequential allocations cannot be merged together they are "chained",
allowing easy per type reserved ranges enumeration and migration to
memblock later. Extra "struct reserved_range" allocated for chaining are
not tracked or reserved but rely on the fact that both
physmem_alloc_range and physmem_alloc_top_down search for free memory
only below current top down allocator position. All reserved ranges
should be transferred to memblock before memblock allocations are
enabled.

The startup code has been reordered to delay any memory allocations until
online memory ranges are detected and occupied memory ranges are marked as
reserved to be excluded from follow-up allocations.
Ipl report certificates are a special case, ipl report certificates list
is checked together with other memory reserves until certificates are
saved elsewhere.
KASAN required memory for shadow memory allocation and mapping is reserved
as 1 large chunk which is later passed to KASAN early initialization code.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

1 files changed, 8 insertions, 105 deletions

diff --git a/arch/s390/boot/kaslr.c b/arch/s390/boot/kaslr.c
index 22b7c5d8e94a..71f75f03f800 100644
--- a/arch/s390/boot/kaslr.c
+++ b/arch/s390/boot/kaslr.c
@@ -91,113 +91,16 @@ static int get_random(unsigned long limit, unsigned long *value)
 	return 0;
 }
 
-/*
- * To randomize kernel base address we have to consider several facts:
- * 1. physical online memory might not be continuous and have holes. physmem
- *    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. physmem online 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_physmem_usable_range(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_physmem_usable_range(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 get_random_base(void)
 {
-	unsigned long usable_total = get_physmem_usable_total();
-	unsigned long memory_limit = get_physmem_usable_end();
-	unsigned long base_pos, max_pos, kernel_size;
-	int i;
+	unsigned long vmlinux_size = vmlinux.image_size + vmlinux.bss_size;
+	unsigned long minimal_pos = vmlinux.default_lma + vmlinux_size;
+	unsigned long random;
 
-	/*
-	 * Avoid putting kernel in the end of physical memory
-	 * which vmem and kasan code will use for shadow memory and
-	 * pgtable mapping allocations.
-	 */
-	memory_limit -= kasan_estimate_memory_needs(usable_total);
-	memory_limit -= vmem_estimate_memory_needs(usable_total);
-
-	safe_addr = ALIGN(safe_addr, THREAD_SIZE);
-	kernel_size = vmlinux.image_size + vmlinux.bss_size;
-	if (safe_addr + kernel_size > memory_limit)
+	/* [vmlinux.default_lma + vmlinux.image_size + vmlinux.bss_size : physmem_info.usable] */
+	if (get_random(physmem_info.usable - minimal_pos, &random))
 		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);
+	return physmem_alloc_range(RR_VMLINUX, vmlinux_size, THREAD_SIZE,
+				   vmlinux.default_lma, minimal_pos + random, false);
 }