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Subject[PATCH v2] x86/mm: Adjust the padding size for KASLR
Date
From: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>

The system sometimes crashes while memory hot-adding on KASLR
enabled system. The crash happens because the regions pointed by
kaslr_regions[].base are overwritten by the hot-added memory.

It happens because of the padding size for kaslr_regions[].base isn't
enough for the system whose physical memory layout has huge space for
memory hotplug. kaslr_regions[].base points "actual installed
memory size + padding" or higher address. So, if the "actual + padding"
is lower address than the maximum memory address, which means the memory
address reachable by memory hot-add, kaslr_regions[].base is destroyed by
the overwritten.

address
^
|------- maximum memory address (Hotplug)
| ^
|------- kaslr_regions[0].base | Hotadd-able region
| ^ |
| | padding |
| V V
|------- actual memory address (Installed on boot)
|

Fix it by getting the maximum memory address from SRAT and store
the value in boot_param, then set the padding size while kaslr
initializing if the default padding size isn't enough.

Signed-off-by: Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>
---
Documentation/x86/zero-page.txt | 4 ++++
arch/x86/boot/compressed/acpi.c | 30 ++++++++++++++++++++-------
arch/x86/include/uapi/asm/bootparam.h | 2 +-
arch/x86/mm/kaslr.c | 29 +++++++++++++++++++++++++-
4 files changed, 56 insertions(+), 9 deletions(-)

diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
index 68aed077f..6c107816c 100644
--- a/Documentation/x86/zero-page.txt
+++ b/Documentation/x86/zero-page.txt
@@ -15,6 +15,7 @@ Offset Proto Name Meaning
058/008 ALL tboot_addr Physical address of tboot shared page
060/010 ALL ist_info Intel SpeedStep (IST) BIOS support information
(struct ist_info)
+078/010 ALL max_addr The possible maximum physical memory address[*].
080/010 ALL hd0_info hd0 disk parameter, OBSOLETE!!
090/010 ALL hd1_info hd1 disk parameter, OBSOLETE!!
0A0/010 ALL sys_desc_table System description table (struct sys_desc_table),
@@ -38,3 +39,6 @@ Offset Proto Name Meaning
2D0/A00 ALL e820_table E820 memory map table
(array of struct e820_entry)
D00/1EC ALL eddbuf EDD data (array of struct edd_info)
+
+[*]: max_addr shows the maximum memory address to be reachable by memory
+ hot-add. max_addr is set by parsing ACPI SRAT.
diff --git a/arch/x86/boot/compressed/acpi.c b/arch/x86/boot/compressed/acpi.c
index c5a949335..3247c7153 100644
--- a/arch/x86/boot/compressed/acpi.c
+++ b/arch/x86/boot/compressed/acpi.c
@@ -272,6 +272,26 @@ static unsigned long get_acpi_srat_table(void)
return 0;
}

+static void subtable_parse(struct acpi_subtable_header *sub_table, int *num,
+ unsigned long *max_addr)
+{
+ struct acpi_srat_mem_affinity *ma;
+ unsigned long addr;
+
+ ma = (struct acpi_srat_mem_affinity *)sub_table;
+ if (ma->length) {
+ if (ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) {
+ addr = ma->base_address + ma->length;
+ if (addr > *max_addr)
+ *max_addr = addr;
+ } else {
+ immovable_mem[*num].start = ma->base_address;
+ immovable_mem[*num].size = ma->length;
+ (*num)++;
+ }
+ }
+}
+
/**
* count_immovable_mem_regions - Parse SRAT and cache the immovable
* memory regions into the immovable_mem array.
@@ -288,6 +308,7 @@ int count_immovable_mem_regions(void)
struct acpi_subtable_header *sub_table;
struct acpi_table_header *table_header;
char arg[MAX_ACPI_ARG_LENGTH];
+ unsigned long max_addr = 0;
int num = 0;

if (cmdline_find_option("acpi", arg, sizeof(arg)) == 3 &&
@@ -305,14 +326,8 @@ int count_immovable_mem_regions(void)
while (table + sizeof(struct acpi_subtable_header) < table_end) {
sub_table = (struct acpi_subtable_header *)table;
if (sub_table->type == ACPI_SRAT_TYPE_MEMORY_AFFINITY) {
- struct acpi_srat_mem_affinity *ma;

- ma = (struct acpi_srat_mem_affinity *)sub_table;
- if (!(ma->flags & ACPI_SRAT_MEM_HOT_PLUGGABLE) && ma->length) {
- immovable_mem[num].start = ma->base_address;
- immovable_mem[num].size = ma->length;
- num++;
- }
+ subtable_parse(sub_table, &num, &max_addr);

if (num >= MAX_NUMNODES*2) {
debug_putstr("Too many immovable memory regions, aborting.\n");
@@ -321,6 +336,7 @@ int count_immovable_mem_regions(void)
}
table += sub_table->length;
}
+ boot_params->max_addr = max_addr;
return num;
}
#endif /* CONFIG_RANDOMIZE_BASE && CONFIG_MEMORY_HOTREMOVE */
diff --git a/arch/x86/include/uapi/asm/bootparam.h b/arch/x86/include/uapi/asm/bootparam.h
index 60733f137..d4882e171 100644
--- a/arch/x86/include/uapi/asm/bootparam.h
+++ b/arch/x86/include/uapi/asm/bootparam.h
@@ -156,7 +156,7 @@ struct boot_params {
__u64 tboot_addr; /* 0x058 */
struct ist_info ist_info; /* 0x060 */
__u64 acpi_rsdp_addr; /* 0x070 */
- __u8 _pad3[8]; /* 0x078 */
+ __u64 max_addr; /* 0x078 */
__u8 hd0_info[16]; /* obsolete! */ /* 0x080 */
__u8 hd1_info[16]; /* obsolete! */ /* 0x090 */
struct sys_desc_table sys_desc_table; /* obsolete! */ /* 0x0a0 */
diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
index 3f452ffed..f44ebfcb7 100644
--- a/arch/x86/mm/kaslr.c
+++ b/arch/x86/mm/kaslr.c
@@ -70,6 +70,33 @@ static inline bool kaslr_memory_enabled(void)
return kaslr_enabled() && !IS_ENABLED(CONFIG_KASAN);
}

+/*
+ * The padding size should set to get for kaslr_regions[].base bigger address
+ * than the maximum memory address the system can have.
+ * kaslr_regions[].base points "actual size + padding" or higher address.
+ * If "actual size + padding" points the lower address than the maximum
+ * memory size, fix the padding size.
+ */
+static unsigned long __init kaslr_padding(void)
+{
+ unsigned long padding = CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+#ifdef CONFIG_MEMORY_HOTPLUG
+ unsigned long actual, maximum, base;
+
+ if (!boot_params.max_addr)
+ goto out;
+
+ actual = roundup(PFN_PHYS(max_pfn), 1UL << TB_SHIFT);
+ maximum = roundup(boot_params.max_addr, 1UL << TB_SHIFT);
+ base = actual + (padding << TB_SHIFT);
+
+ if (maximum > base)
+ padding = (maximum - actual) >> TB_SHIFT;
+out:
+#endif
+ return padding;
+}
+
/* Initialize base and padding for each memory region randomized with KASLR */
void __init kernel_randomize_memory(void)
{
@@ -103,7 +130,7 @@ void __init kernel_randomize_memory(void)
*/
BUG_ON(kaslr_regions[0].base != &page_offset_base);
memory_tb = DIV_ROUND_UP(max_pfn << PAGE_SHIFT, 1UL << TB_SHIFT) +
- CONFIG_RANDOMIZE_MEMORY_PHYSICAL_PADDING;
+ kaslr_padding();

/* Adapt phyiscal memory region size based on available memory */
if (memory_tb < kaslr_regions[0].size_tb)
--
2.20.1
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