Re: [PATCH 1/1] riscv: Add support to dump the kernel page tables
From: Zong Li
Date: Thu Oct 24 2019 - 22:22:47 EST
On Thu, Oct 24, 2019 at 10:34 PM Steven Price <steven.price@xxxxxxx> wrote:
>
> On 24/10/2019 14:02, Zong Li wrote:
> > 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@xxxxxxxxxx>
>
> Great to see someone pick this up for another architecture. I'm not very
> familiar with riscv, so I can't review the arch aspects, but one minor
> comment below.
>
> > ---
> > arch/riscv/Kconfig | 1 +
> > arch/riscv/include/asm/pgtable.h | 10 ++
> > arch/riscv/include/asm/ptdump.h | 19 +++
> > arch/riscv/mm/Makefile | 1 +
> > arch/riscv/mm/ptdump.c | 309 +++++++++++++++++++++++++++++++++++++++
> > 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 bc7598f..053cb7a 100644
> > --- a/arch/riscv/Kconfig
> > +++ b/arch/riscv/Kconfig
> > @@ -25,6 +25,7 @@ config RISCV
> > select GENERIC_CPU_DEVICES
> > select GENERIC_IRQ_SHOW
> > select GENERIC_PCI_IOMAP
> > + select GENERIC_PTDUMP
> > select GENERIC_SCHED_CLOCK
> > select GENERIC_STRNCPY_FROM_USER
> > select GENERIC_STRNLEN_USER
> > diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> > index df6522d..be93e59 100644
> > --- a/arch/riscv/include/asm/pgtable.h
> > +++ b/arch/riscv/include/asm/pgtable.h
> > @@ -444,6 +444,16 @@ extern void setup_bootmem(void);
> > extern void paging_init(void);
> >
> > /*
> > + * 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 0000000..26d9221
> > --- /dev/null
> > +++ b/arch/riscv/include/asm/ptdump.h
> > @@ -0,0 +1,19 @@
> > +/* SPDX-License-Identifier: GPL-2.0 */
> > +/*
> > + * Copyright (C) 2019 SiFive
> > + */
> > +
> > +#ifndef _ASM_RISCV_PTDUMP_H
> > +#define _ASM_RISCV_PTDUMP_H
> > +
> > +#ifdef CONFIG_PTDUMP_CORE
> > +void ptdump_check_wx(void);
> > +#endif /* CONFIG_PTDUMP_CORE */
>
> I believe this file is only included from ptdump.c which is only build
> when CONFIG_PTDUMP_CORE is set. So the #ifdeffery isn't necessary.
Yes, make sense, I will remove the condition there. Actually, I'm
working on STRICT_KERNEL_RWX too, it will include the ptdump.h in
another file for using debug_checkwx, but the condition is still
unnecessary, because ptdump_check_wx() is only used when
CONFIG_DEBUG_WX is enabled, and CONFIG_DEBUG_WX always selects the
CONFIG_PTDUMP_CORE.
Thanks to you for the suggestion.
> Thanks,
>
> Steve
>
> > +
> > +#ifdef CONFIG_DEBUG_WX
> > +#define debug_checkwx() ptdump_check_wx()
> > +#else
> > +#define debug_checkwx() do { } while (0)
> > +#endif
> > +
> > +#endif /* _ASM_RISCV_PTDUMP_H */
> > diff --git a/arch/riscv/mm/Makefile b/arch/riscv/mm/Makefile
> > index 9d9a173..d6132f8 100644
> > --- a/arch/riscv/mm/Makefile
> > +++ b/arch/riscv/mm/Makefile
> > @@ -17,3 +17,4 @@ ifeq ($(CONFIG_MMU),y)
> > obj-$(CONFIG_SMP) += tlbflush.o
> > endif
> > obj-$(CONFIG_HUGETLB_PAGE) += hugetlbpage.o
> > +obj-$(CONFIG_PTDUMP_CORE) += ptdump.o
> > diff --git a/arch/riscv/mm/ptdump.c b/arch/riscv/mm/ptdump.c
> > new file mode 100644
> > index 0000000..60c8af1
> > --- /dev/null
> > +++ b/arch/riscv/mm/ptdump.c
> > @@ -0,0 +1,309 @@
> > +// 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>
> > +
> > +#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[] = {
> > + {FIXADDR_START, "Fixmap start"},
> > + {FIXADDR_TOP, "Fixmap 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) {
> > + 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,
> > + .ptdump = {
> > + .note_page = note_page,
> > + .range = (struct ptdump_range[]) {
> > + {KERN_VIRT_START, ULONG_MAX},
> > + {0, 0}
> > + }
> > + }
> > + };
> > +
> > + ptdump_walk_pgd(&st.ptdump, &init_mm);
> > +}
> > +
> > +void ptdump_check_wx(void)
> > +{
> > + struct pg_state st = {
> > + .seq = NULL,
> > + .marker = (struct addr_marker[]) {
> > + {0, NULL},
> > + {-1, NULL},
> > + },
> > + .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);
> > +
> > + 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);
> >
>