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Subject[PATCH v3 1/2] riscv: Add support to dump the kernel page tables
Date
In a similar manner to arm64, x86, powerpc, etc., it can traverse all
page tables, and dump the page table layout with the memory types and
permissions.

Add a debugfs file at /sys/kernel/debug/kernel_page_tables to export
the page table layout to userspace.

Signed-off-by: Zong Li <zong.li@sifive.com>
Tested-by: Alexandre Ghiti <alex@ghiti.fr>
---
arch/riscv/Kconfig | 1 +
arch/riscv/include/asm/pgtable.h | 10 +
arch/riscv/include/asm/ptdump.h | 11 ++
arch/riscv/mm/Makefile | 1 +
arch/riscv/mm/ptdump.c | 317 +++++++++++++++++++++++++++++++
5 files changed, 340 insertions(+)
create mode 100644 arch/riscv/include/asm/ptdump.h
create mode 100644 arch/riscv/mm/ptdump.c

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1a3b5a5276be..735b91014f79 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -29,6 +29,7 @@ config RISCV
select GENERIC_SMP_IDLE_THREAD
select GENERIC_ATOMIC64 if !64BIT
select GENERIC_IOREMAP
+ select GENERIC_PTDUMP if MMU
select HAVE_ARCH_AUDITSYSCALL
select HAVE_ARCH_SECCOMP_FILTER
select HAVE_ASM_MODVERSIONS
diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index e43041519edd..ac353e44f80c 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -444,6 +444,16 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
#endif
#define FIXADDR_START (FIXADDR_TOP - FIXADDR_SIZE)

+/*
+ * In the RV64 Linux scheme, we give the user half of the virtual-address space
+ * and give the kernel the other (upper) half.
+ */
+#ifdef CONFIG_64BIT
+#define KERN_VIRT_START (-(BIT(CONFIG_VA_BITS)) + TASK_SIZE)
+#else
+#define KERN_VIRT_START FIXADDR_START
+#endif
+
/*
* Task size is 0x4000000000 for RV64 or 0x9fc00000 for RV32.
* Note that PGDIR_SIZE must evenly divide TASK_SIZE.
diff --git a/arch/riscv/include/asm/ptdump.h b/arch/riscv/include/asm/ptdump.h
new file mode 100644
index 000000000000..e29af7191909
--- /dev/null
+++ b/arch/riscv/include/asm/ptdump.h
@@ -0,0 +1,11 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2019 SiFive
+ */
+
+#ifndef _ASM_RISCV_PTDUMP_H
+#define _ASM_RISCV_PTDUMP_H
+
+void ptdump_check_wx(void);
+
+#endif /* _ASM_RISCV_PTDUMP_H */
diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
index 50b7af58c566..814e16a8d68a 100644
--- a/arch/riscv/mm/Makefile
+++ b/arch/riscv/mm/Makefile
@@ -15,6 +15,7 @@ ifeq ($(CONFIG_MMU),y)
obj-$(CONFIG_SMP) += tlbflush.o
endif
obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
+obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
obj-$(CONFIG_KASAN) += kasan_init.o

ifdef CONFIG_KASAN
diff --git a/arch/riscv/mm/ptdump.c b/arch/riscv/mm/ptdump.c
new file mode 100644
index 000000000000..7eab76a93106
--- /dev/null
+++ b/arch/riscv/mm/ptdump.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2019 SiFive
+ */
+
+#include <linux/init.h>
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+#include <linux/ptdump.h>
+
+#include <asm/ptdump.h>
+#include <asm/pgtable.h>
+#include <asm/kasan.h>
+
+#define pt_dump_seq_printf(m, fmt, args...) \
+({ \
+ if (m) \
+ seq_printf(m, fmt, ##args); \
+})
+
+#define pt_dump_seq_puts(m, fmt) \
+({ \
+ if (m) \
+ seq_printf(m, fmt); \
+})
+
+/*
+ * The page dumper groups page table entries of the same type into a single
+ * description. It uses pg_state to track the range information while
+ * iterating over the pte entries. When the continuity is broken it then
+ * dumps out a description of the range.
+ */
+struct pg_state {
+ struct ptdump_state ptdump;
+ struct seq_file *seq;
+ const struct addr_marker *marker;
+ unsigned long start_address;
+ unsigned long start_pa;
+ unsigned long last_pa;
+ int level;
+ u64 current_prot;
+ bool check_wx;
+ unsigned long wx_pages;
+};
+
+/* Address marker */
+struct addr_marker {
+ unsigned long start_address;
+ const char *name;
+};
+
+static struct addr_marker address_markers[] = {
+#ifdef CONFIG_KASAN
+ {KASAN_SHADOW_START, "Kasan shadow start"},
+ {KASAN_SHADOW_END, "Kasan shadow end"},
+#endif
+ {FIXADDR_START, "Fixmap start"},
+ {FIXADDR_TOP, "Fixmap end"},
+ {PCI_IO_START, "PCI I/O start"},
+ {PCI_IO_END, "PCI I/O end"},
+#ifdef CONFIG_SPARSEMEM_VMEMMAP
+ {VMEMMAP_START, "vmemmap start"},
+ {VMEMMAP_END, "vmemmap end"},
+#endif
+ {VMALLOC_START, "vmalloc() area"},
+ {VMALLOC_END, "vmalloc() end"},
+ {PAGE_OFFSET, "Linear mapping"},
+ {-1, NULL},
+};
+
+/* Page Table Entry */
+struct prot_bits {
+ u64 mask;
+ u64 val;
+ const char *set;
+ const char *clear;
+};
+
+static const struct prot_bits pte_bits[] = {
+ {
+ .mask = _PAGE_SOFT,
+ .val = _PAGE_SOFT,
+ .set = "RSW",
+ .clear = " ",
+ }, {
+ .mask = _PAGE_DIRTY,
+ .val = _PAGE_DIRTY,
+ .set = "D",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_ACCESSED,
+ .val = _PAGE_ACCESSED,
+ .set = "A",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_GLOBAL,
+ .val = _PAGE_GLOBAL,
+ .set = "G",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_USER,
+ .val = _PAGE_USER,
+ .set = "U",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_EXEC,
+ .val = _PAGE_EXEC,
+ .set = "X",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_WRITE,
+ .val = _PAGE_WRITE,
+ .set = "W",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_READ,
+ .val = _PAGE_READ,
+ .set = "R",
+ .clear = ".",
+ }, {
+ .mask = _PAGE_PRESENT,
+ .val = _PAGE_PRESENT,
+ .set = "V",
+ .clear = ".",
+ }
+};
+
+/* Page Level */
+struct pg_level {
+ const char *name;
+ u64 mask;
+};
+
+static struct pg_level pg_level[] = {
+ { /* pgd */
+ .name = "PGD",
+ }, { /* p4d */
+ .name = (CONFIG_PGTABLE_LEVELS > 4) ? "P4D" : "PGD",
+ }, { /* pud */
+ .name = (CONFIG_PGTABLE_LEVELS > 3) ? "PUD" : "PGD",
+ }, { /* pmd */
+ .name = (CONFIG_PGTABLE_LEVELS > 2) ? "PMD" : "PGD",
+ }, { /* pte */
+ .name = "PTE",
+ },
+};
+
+static void dump_prot(struct pg_state *st)
+{
+ unsigned int i;
+
+ for (i = 0; i < ARRAY_SIZE(pte_bits); i++) {
+ const char *s;
+
+ if ((st->current_prot & pte_bits[i].mask) == pte_bits[i].val)
+ s = pte_bits[i].set;
+ else
+ s = pte_bits[i].clear;
+
+ if (s)
+ pt_dump_seq_printf(st->seq, " %s", s);
+ }
+}
+
+#ifdef CONFIG_64BIT
+#define ADDR_FORMAT "0x%016lx"
+#else
+#define ADDR_FORMAT "0x%08lx"
+#endif
+static void dump_addr(struct pg_state *st, unsigned long addr)
+{
+ static const char units[] = "KMGTPE";
+ const char *unit = units;
+ unsigned long delta;
+
+ pt_dump_seq_printf(st->seq, ADDR_FORMAT "-" ADDR_FORMAT " ",
+ st->start_address, addr);
+
+ pt_dump_seq_printf(st->seq, " " ADDR_FORMAT " ", st->start_pa);
+ delta = (addr - st->start_address) >> 10;
+
+ while (!(delta & 1023) && unit[1]) {
+ delta >>= 10;
+ unit++;
+ }
+
+ pt_dump_seq_printf(st->seq, "%9lu%c %s", delta, *unit,
+ pg_level[st->level].name);
+}
+
+static void note_prot_wx(struct pg_state *st, unsigned long addr)
+{
+ if (!st->check_wx)
+ return;
+
+ if ((st->current_prot & (_PAGE_WRITE | _PAGE_EXEC)) !=
+ (_PAGE_WRITE | _PAGE_EXEC))
+ return;
+
+ WARN_ONCE(1, "riscv/mm: Found insecure W+X mapping at address %p/%pS\n",
+ (void *)st->start_address, (void *)st->start_address);
+
+ st->wx_pages += (addr - st->start_address) / PAGE_SIZE;
+}
+
+static void note_page(struct ptdump_state *pt_st, unsigned long addr,
+ int level, unsigned long val)
+{
+ struct pg_state *st = container_of(pt_st, struct pg_state, ptdump);
+ u64 pa = PFN_PHYS(pte_pfn(__pte(val)));
+ u64 prot = 0;
+
+ if (level >= 0)
+ prot = val & pg_level[level].mask;
+
+ if (st->level == -1) {
+ st->level = level;
+ st->current_prot = prot;
+ st->start_address = addr;
+ st->start_pa = pa;
+ st->last_pa = pa;
+ pt_dump_seq_printf(st->seq, "---[ %s ]---\n", st->marker->name);
+ } else if (prot != st->current_prot ||
+ level != st->level || addr >= st->marker[1].start_address) {
+ if (st->current_prot) {
+ note_prot_wx(st, addr);
+ dump_addr(st, addr);
+ dump_prot(st);
+ pt_dump_seq_puts(st->seq, "\n");
+ }
+
+ while (addr >= st->marker[1].start_address) {
+ st->marker++;
+ pt_dump_seq_printf(st->seq, "---[ %s ]---\n",
+ st->marker->name);
+ }
+
+ st->start_address = addr;
+ st->start_pa = pa;
+ st->last_pa = pa;
+ st->current_prot = prot;
+ st->level = level;
+ } else {
+ st->last_pa = pa;
+ }
+}
+
+static void ptdump_walk(struct seq_file *s)
+{
+ struct pg_state st = {
+ .seq = s,
+ .marker = address_markers,
+ .level = -1,
+ .ptdump = {
+ .note_page = note_page,
+ .range = (struct ptdump_range[]) {
+ {KERN_VIRT_START, ULONG_MAX},
+ {0, 0}
+ }
+ }
+ };
+
+ ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
+}
+
+void ptdump_check_wx(void)
+{
+ struct pg_state st = {
+ .seq = NULL,
+ .marker = (struct addr_marker[]) {
+ {0, NULL},
+ {-1, NULL},
+ },
+ .level = -1,
+ .check_wx = true,
+ .ptdump = {
+ .note_page = note_page,
+ .range = (struct ptdump_range[]) {
+ {KERN_VIRT_START, ULONG_MAX},
+ {0, 0}
+ }
+ }
+ };
+
+ ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
+
+ if (st.wx_pages)
+ pr_warn("Checked W+X mappings: failed, %lu W+X pages found\n",
+ st.wx_pages);
+ else
+ pr_info("Checked W+X mappings: passed, no W+X pages found\n");
+}
+
+static int ptdump_show(struct seq_file *m, void *v)
+{
+ ptdump_walk(m);
+
+ return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(ptdump);
+
+static int ptdump_init(void)
+{
+ unsigned int i, j;
+
+ for (i = 0; i < ARRAY_SIZE(pg_level); i++)
+ for (j = 0; j < ARRAY_SIZE(pte_bits); j++)
+ pg_level[i].mask |= pte_bits[j].mask;
+
+ debugfs_create_file("kernel_page_tables", 0400, NULL, NULL,
+ &ptdump_fops);
+
+ return 0;
+}
+
+device_initcall(ptdump_init);
--
2.25.1
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