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    Subject[PATCH v9 19/21] mm: Add generic ptdump
    Date
    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 | 161 +++++++++++++++++++++++++++++++++++++++++
    4 files changed, 202 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 82b6a20898bd..7ad939b7140f 100644
    --- a/mm/Kconfig.debug
    +++ b/mm/Kconfig.debug
    @@ -115,3 +115,24 @@ 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 kernel 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 338e528ad436..750a4c12d5da 100644
    --- a/mm/Makefile
    +++ b/mm/Makefile
    @@ -104,3 +104,4 @@ obj-$(CONFIG_HARDENED_USERCOPY) += usercopy.o
    obj-$(CONFIG_PERCPU_STATS) += percpu-stats.o
    obj-$(CONFIG_HMM_MIRROR) += hmm.o
    obj-$(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..39befc9088b8
    --- /dev/null
    +++ b/mm/ptdump.c
    @@ -0,0 +1,161 @@
    +// 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_leaf(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_leaf(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_leaf(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_leaf(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) ||
    +#ifdef CONFIG_X86
    + (pgtable_l5_enabled() &&
    + __pa(pt) == __pa(kasan_early_shadow_p4d)) ||
    +#endif
    + __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
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