[RFC PATCH 1/3] mm: Add generic ptdump

Steven Price
2019-04-17T14:34:37Z

Add a generic version of page table dumping that architectures can
opt-in to

Signed-off-by: Steven Price <steven.price@arm.com>
---
include/linux/ptdump.h | 19 +++++
mm/Kconfig.debug | 21 ++++++
mm/Makefile | 1 +
mm/ptdump.c | 159 +++++++++++++++++++++++++++++++++++++++++
4 files changed, 200 insertions(+)
create mode 100644 include/linux/ptdump.h
create mode 100644 mm/ptdump.c

diff --git a/include/linux/ptdump.h b/include/linux/ptdump.h
new file mode 100644
index 000000000000..eb8e78154be3
--- /dev/null
+++ b/include/linux/ptdump.h
@@ -0,0 +1,19 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef _LINUX_PTDUMP_H
+#define _LINUX_PTDUMP_H
+
+struct ptdump_range {
+ unsigned long start;
+ unsigned long end;
+};
+
+struct ptdump_state {
+ void (*note_page)(struct ptdump_state *st, unsigned long addr,
+ int level, unsigned long val);
+ const struct ptdump_range *range;
+};
+
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm);
+
+#endif /* _LINUX_PTDUMP_H */
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index e3df921208c0..21bbf559408b 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -111,3 +111,24 @@ config DEBUG_RODATA_TEST
depends on STRICT_KERNEL_RWX
---help---
This option enables a testcase for the setting rodata read-only.
+
+config GENERIC_PTDUMP
+ bool
+
+config PTDUMP_CORE
+ bool
+
+config PTDUMP_DEBUGFS
+ bool "Export kerenl pagetable layout to userspace via debugfs"
+ depends on DEBUG_KERNEL
+ depends on DEBUG_FS
+ depends on GENERIC_PTDUMP
+ select PTDUMP_CORE
+ help
+ Say Y here if you want to show the kernel pagetable layout in a
+ debugfs file. This information is only useful for kernel developers
+ who are working in architecture specific areas of the kernel.
+ It is probably not a good idea to enable this feature in a production
+ kernel.
+
+ If in doubt, say N.
diff --git a/mm/Makefile b/mm/Makefile
index d210cc9d6f80..59d653c3250d 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -99,3 +99,4 @@ obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
obj-$(CONFIG_HMM) += hmm.o
obj-$(CONFIG_MEMFD_CREATE) += memfd.o
+obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
diff --git a/mm/ptdump.c b/mm/ptdump.c
new file mode 100644
index 000000000000..c8e4c08ce206
--- /dev/null
+++ b/mm/ptdump.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/mm.h>
+#include <linux/ptdump.h>
+#include <linux/kasan.h>
+
+static int ptdump_pgd_entry(pgd_t *pgd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pgd_t val = READ_ONCE(*pgd);
+
+ if (pgd_large(val))
+ st->note_page(st, addr, 1, pgd_val(val));
+
+ return 0;
+}
+
+static int ptdump_p4d_entry(p4d_t *p4d, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ p4d_t val = READ_ONCE(*p4d);
+
+ if (p4d_large(val))
+ st->note_page(st, addr, 2, p4d_val(val));
+
+ return 0;
+}
+
+static int ptdump_pud_entry(pud_t *pud, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pud_t val = READ_ONCE(*pud);
+
+ if (pud_large(val))
+ st->note_page(st, addr, 3, pud_val(val));
+
+ return 0;
+}
+
+static int ptdump_pmd_entry(pmd_t *pmd, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+ pmd_t val = READ_ONCE(*pmd);
+
+ if (pmd_large(val))
+ st->note_page(st, addr, 4, pmd_val(val));
+
+ return 0;
+}
+
+static int ptdump_pte_entry(pte_t *pte, unsigned long addr,
+ unsigned long next, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ st->note_page(st, addr, 5, pte_val(READ_ONCE(*pte)));
+
+ return 0;
+}
+
+#ifdef CONFIG_KASAN
+/*
+ * This is an optimization for KASAN=y case. Since all kasan page tables
+ * eventually point to the kasan_early_shadow_page we could call note_page()
+ * right away without walking through lower level page tables. This saves
+ * us dozens of seconds (minutes for 5-level config) while checking for
+ * W+X mapping or reading kernel_page_tables debugfs file.
+ */
+static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
+ unsigned long addr)
+{
+ if (__pa(pt) == __pa(kasan_early_shadow_pmd) ||
+ (pgtable_l5_enabled() &&
+ __pa(pt) == __pa(kasan_early_shadow_p4d)) ||
+ __pa(pt) == __pa(kasan_early_shadow_pud)) {
+ st->note_page(st, addr, 5, pte_val(kasan_early_shadow_pte[0]));
+ return true;
+ }
+ return false;
+}
+#else
+static inline bool kasan_page_table(struct ptdump_state *st, void *pt,
+ unsigned long addr)
+{
+ return false;
+}
+#endif
+
+static int ptdump_test_p4d(unsigned long addr, unsigned long next,
+ p4d_t *p4d, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ if (kasan_page_table(st, p4d, addr))
+ return 1;
+ return 0;
+}
+
+static int ptdump_test_pud(unsigned long addr, unsigned long next,
+ pud_t *pud, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ if (kasan_page_table(st, pud, addr))
+ return 1;
+ return 0;
+}
+
+static int ptdump_test_pmd(unsigned long addr, unsigned long next,
+ pmd_t *pmd, struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ if (kasan_page_table(st, pmd, addr))
+ return 1;
+ return 0;
+}
+
+static int ptdump_hole(unsigned long addr, unsigned long next,
+ struct mm_walk *walk)
+{
+ struct ptdump_state *st = walk->private;
+
+ st->note_page(st, addr, -1, 0);
+
+ return 0;
+}
+
+void ptdump_walk_pgd(struct ptdump_state *st, struct mm_struct *mm)
+{
+ struct mm_walk walk = {
+ .mm = mm,
+ .pgd_entry = ptdump_pgd_entry,
+ .p4d_entry = ptdump_p4d_entry,
+ .pud_entry = ptdump_pud_entry,
+ .pmd_entry = ptdump_pmd_entry,
+ .pte_entry = ptdump_pte_entry,
+ .test_p4d = ptdump_test_p4d,
+ .test_pud = ptdump_test_pud,
+ .test_pmd = ptdump_test_pmd,
+ .pte_hole = ptdump_hole,
+ .private = st
+ };
+ const struct ptdump_range *range = st->range;
+
+ down_read(&mm->mmap_sem);
+ while (range->start != range->end) {
+ walk_page_range(range->start, range->end, &walk);
+ range++;
+ }
+ up_read(&mm->mmap_sem);
+
+ /* Flush out the last page */
+ st->note_page(st, 0, 0, 0);
+}
--
2.20.1