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Message-ID: <tip-d2aa1acad22f1bdd0cfa67b3861800e392254454@git.kernel.org>
Date: Mon, 22 Feb 2016 04:18:45 -0800
From: tip-bot for Kees Cook <tipbot@...or.com>@zytor.com
To: linux-tip-commits@...r.kernel.org@...or.com
Cc: minipli@...glemail.com, mpe@...erman.id.au,
linux-arch@...r.kernel.org, david.brown@...aro.org, arnd@...db.de,
keescook@...omium.org, bp@...en8.de, torvalds@...ux-foundation.org,
pageexec@...email.hu, linux-kernel@...r.kernel.org,
brgerst@...il.com, luto@...capital.net, mingo@...nel.org,
tglx@...utronix.de, hpa@...or.com, re.emese@...il.com,
peterz@...radead.org, dvlasenk@...hat.com
Subject: [tip:mm/readonly] mm/init: Add 'rodata=off' boot cmdline parameter to disable read-only kernel mappings
Commit-ID: d2aa1acad22f1bdd0cfa67b3861800e392254454
Gitweb: http://git.kernel.org/tip/d2aa1acad22f1bdd0cfa67b3861800e392254454
Author: Kees Cook <keescook@...omium.org>
AuthorDate: Wed, 17 Feb 2016 14:41:13 -0800
Committer: Ingo Molnar <mingo@...nel.org>
CommitDate: Mon, 22 Feb 2016 08:51:37 +0100
mm/init: Add 'rodata=off' boot cmdline parameter to disable read-only kernel mappings
It may be useful to debug writes to the readonly sections of memory,
so provide a cmdline "rodata=off" to allow for this. This can be
expanded in the future to support "log" and "write" modes, but that
will need to be architecture-specific.
This also makes KDB software breakpoints more usable, as read-only
mappings can now be disabled on any kernel.
Suggested-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Kees Cook <keescook@...omium.org>
Cc: Andy Lutomirski <luto@...capital.net>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Brian Gerst <brgerst@...il.com>
Cc: David Brown <david.brown@...aro.org>
Cc: Denys Vlasenko <dvlasenk@...hat.com>
Cc: Emese Revfy <re.emese@...il.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathias Krause <minipli@...glemail.com>
Cc: Michael Ellerman <mpe@...erman.id.au>
Cc: PaX Team <pageexec@...email.hu>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: kernel-hardening@...ts.openwall.com
Cc: linux-arch <linux-arch@...r.kernel.org>
Link: http://lkml.kernel.org/r/1455748879-21872-3-git-send-email-keescook@chromium.org
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
Documentation/kernel-parameters.txt | 4 ++++
init/main.c | 27 +++++++++++++++++++++++----
kernel/debug/kdb/kdb_bp.c | 4 +---
3 files changed, 28 insertions(+), 7 deletions(-)
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 9a53c92..0003367 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3491,6 +3491,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
ro [KNL] Mount root device read-only on boot
+ rodata= [KNL]
+ on Mark read-only kernel memory as read-only (default).
+ off Leave read-only kernel memory writable for debugging.
+
root= [KNL] Root filesystem
See name_to_dev_t comment in init/do_mounts.c.
diff --git a/init/main.c b/init/main.c
index 58c9e37..928a343 100644
--- a/init/main.c
+++ b/init/main.c
@@ -93,9 +93,6 @@ static int kernel_init(void *);
extern void init_IRQ(void);
extern void fork_init(void);
extern void radix_tree_init(void);
-#ifndef CONFIG_DEBUG_RODATA
-static inline void mark_rodata_ro(void) { }
-#endif
/*
* Debug helper: via this flag we know that we are in 'early bootup code'
@@ -929,6 +926,28 @@ static int try_to_run_init_process(const char *init_filename)
static noinline void __init kernel_init_freeable(void);
+#ifdef CONFIG_DEBUG_RODATA
+static bool rodata_enabled = true;
+static int __init set_debug_rodata(char *str)
+{
+ return strtobool(str, &rodata_enabled);
+}
+__setup("rodata=", set_debug_rodata);
+
+static void mark_readonly(void)
+{
+ if (rodata_enabled)
+ mark_rodata_ro();
+ else
+ pr_info("Kernel memory protection disabled.\n");
+}
+#else
+static inline void mark_readonly(void)
+{
+ pr_warn("This architecture does not have kernel memory protection.\n");
+}
+#endif
+
static int __ref kernel_init(void *unused)
{
int ret;
@@ -937,7 +956,7 @@ static int __ref kernel_init(void *unused)
/* need to finish all async __init code before freeing the memory */
async_synchronize_full();
free_initmem();
- mark_rodata_ro();
+ mark_readonly();
system_state = SYSTEM_RUNNING;
numa_default_policy();
diff --git a/kernel/debug/kdb/kdb_bp.c b/kernel/debug/kdb/kdb_bp.c
index e1dbf4a..90ff129 100644
--- a/kernel/debug/kdb/kdb_bp.c
+++ b/kernel/debug/kdb/kdb_bp.c
@@ -153,13 +153,11 @@ static int _kdb_bp_install(struct pt_regs *regs, kdb_bp_t *bp)
} else {
kdb_printf("%s: failed to set breakpoint at 0x%lx\n",
__func__, bp->bp_addr);
-#ifdef CONFIG_DEBUG_RODATA
if (!bp->bp_type) {
kdb_printf("Software breakpoints are unavailable.\n"
- " Change the kernel CONFIG_DEBUG_RODATA=n\n"
+ " Boot the kernel with rodata=off\n"
" OR use hw breaks: help bph\n");
}
-#endif
return 1;
}
return 0;
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