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Message-Id: <20160929213257.30505-4-labbott@redhat.com>
Date: Thu, 29 Sep 2016 14:32:57 -0700
From: Laura Abbott <labbott@...hat.com>
To: AKASHI Takahiro <takahiro.akashi@...aro.org>,
Mark Rutland <mark.rutland@....com>,
Ard Biesheuvel <ard.biesheuvel@...aro.org>,
David Brown <david.brown@...aro.org>,
Will Deacon <will.deacon@....com>,
Catalin Marinas <catalin.marinas@....com>
Cc: Laura Abbott <labbott@...hat.com>,
linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org,
Kees Cook <keescook@...omium.org>,
kernel-hardening@...ts.openwall.com
Subject: [PATCH 3/3] arm64: dump: Add checking for writable and exectuable pages
Page mappings with full RWX permissions are a security risk. x86
has an option to walk the page tables and dump any bad pages.
(See e1a58320a38d ("x86/mm: Warn on W^X mappings")). Add a similar
implementation for arm64.
Signed-off-by: Laura Abbott <labbott@...hat.com>
---
arch/arm64/Kconfig.debug | 28 ++++++++++++++++++++++++++++
arch/arm64/include/asm/ptdump.h | 10 ++++++++++
arch/arm64/mm/dump.c | 36 ++++++++++++++++++++++++++++++++++++
arch/arm64/mm/mmu.c | 2 ++
4 files changed, 76 insertions(+)
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index 9015f02..037dba4 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -42,6 +42,34 @@ config ARM64_RANDOMIZE_TEXT_OFFSET
of TEXT_OFFSET and platforms must not require a specific
value.
+config DEBUG_WX
+ bool "Warn on W+X mappings at boot"
+ select ARM64_PTDUMP_CORE
+ ---help---
+ Generate a warning if any W+X mappings are found at boot.
+
+ This is useful for discovering cases where the kernel is leaving
+ W+X mappings after applying NX, as such mappings are a security risk.
+
+ Look for a message in dmesg output like this:
+
+ arm64/mm: Checked W+X mappings: passed, no W+X pages found.
+
+ or like this, if the check failed:
+
+ arm64/mm: Checked W+X mappings: FAILED, <N> W+X pages found.
+
+ Note that even if the check fails, your kernel is possibly
+ still fine, as W+X mappings are not a security hole in
+ themselves, what they do is that they make the exploitation
+ of other unfixed kernel bugs easier.
+
+ There is no runtime or memory usage effect of this option
+ once the kernel has booted up - it's a one time check.
+
+ If in doubt, say "Y".
+
+
config DEBUG_SET_MODULE_RONX
bool "Set loadable kernel module data as NX and text as RO"
depends on MODULES
diff --git a/arch/arm64/include/asm/ptdump.h b/arch/arm64/include/asm/ptdump.h
index b18a62c..e3c6bc0 100644
--- a/arch/arm64/include/asm/ptdump.h
+++ b/arch/arm64/include/asm/ptdump.h
@@ -20,6 +20,7 @@
#include <linux/seq_file.h>
#include <linux/mm_types.h>
+#include <linux/list.h>
struct addr_marker {
unsigned long start_address;
@@ -31,6 +32,8 @@ struct ptdump_info {
const struct addr_marker *markers;
unsigned long base_addr;
unsigned long max_addr;
+ /* Internal, do not touch */
+ struct list_head node;
};
int ptdump_register(struct ptdump_info *info, const char *name);
@@ -44,6 +47,13 @@ static inline int ptdump_debugfs_create(struct ptdump_info *info,
return 0;
}
#endif
+void ptdump_check_wx(void);
+
+#ifdef CONFIG_DEBUG_WX
+#define debug_checkwx() ptdump_check_wx()
+#else
+#define debug_checkwx() do { } while (0)
+#endif
#else
static inline int ptdump_register(struct ptdump_info *info, const char *name)
diff --git a/arch/arm64/mm/dump.c b/arch/arm64/mm/dump.c
index e318f3d..b0b1dd6 100644
--- a/arch/arm64/mm/dump.c
+++ b/arch/arm64/mm/dump.c
@@ -29,6 +29,8 @@
#include <asm/pgtable-hwdef.h>
#include <asm/ptdump.h>
+static LIST_HEAD(dump_info);
+
static const struct addr_marker address_markers[] = {
#ifdef CONFIG_KASAN
{ KASAN_SHADOW_START, "Kasan shadow start" },
@@ -74,6 +76,8 @@ struct pg_state {
unsigned long start_address;
unsigned level;
u64 current_prot;
+ bool check_wx;
+ unsigned long wx_pages;
};
struct prot_bits {
@@ -219,6 +223,15 @@ static void note_page(struct pg_state *st, unsigned long addr, unsigned level,
unsigned long delta;
if (st->current_prot) {
+ if (st->check_wx &&
+ ((st->current_prot & PTE_RDONLY) != PTE_RDONLY) &&
+ ((st->current_prot & PTE_PXN) != PTE_PXN)) {
+ WARN_ONCE(1, "arm64/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;
+ }
+
pt_dump_seq_printf(st->seq, "0x%016lx-0x%016lx ",
st->start_address, addr);
@@ -341,6 +354,7 @@ static void ptdump_initialize(struct ptdump_info *info)
int ptdump_register(struct ptdump_info *info, const char *name)
{
ptdump_initialize(info);
+ list_add(&info->node, &dump_info);
return ptdump_debugfs_create(info, name);
}
@@ -350,6 +364,28 @@ static struct ptdump_info kernel_ptdump_info = {
.base_addr = VA_START,
};
+void ptdump_check_wx(void)
+{
+ struct ptdump_info *info;
+
+ list_for_each_entry(info, &dump_info, node) {
+ struct pg_state st = {
+ .seq = NULL,
+ .marker = info->markers,
+ .check_wx = true,
+ };
+
+ __walk_pgd(&st, info->mm, info->base_addr);
+ note_page(&st, 0, 0, 0);
+ if (st.wx_pages)
+ pr_info("Checked W+X mappings (%p): FAILED, %lu W+X pages found\n",
+ info->mm,
+ st.wx_pages);
+ else
+ pr_info("Checked W+X mappings (%p): passed, no W+X pages found\n", info->mm);
+ }
+}
+
static int ptdump_init(void)
{
return ptdump_register(&kernel_ptdump_info, "kernel_page_tables");
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index 4989948..1f036d2 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -41,6 +41,7 @@
#include <asm/tlb.h>
#include <asm/memblock.h>
#include <asm/mmu_context.h>
+#include <asm/ptdump.h>
#include "mm.h"
@@ -397,6 +398,7 @@ void mark_rodata_ro(void)
section_size = (unsigned long)__init_begin - (unsigned long)__start_rodata;
create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata,
section_size, PAGE_KERNEL_RO);
+ debug_checkwx();
}
void fixup_init(void)
--
2.10.0
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