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Message-Id: <1449697404-21076-5-git-send-email-keescook@chromium.org>
Date: Wed, 9 Dec 2015 13:43:20 -0800
From: Kees Cook <keescook@...omium.org>
To: linux-kernel@...r.kernel.org
Cc: Kees Cook <keescook@...omium.org>, Ingo Molnar <mingo@...hat.com>,
Andy Lutomirski <luto@...capital.net>,
"H. Peter Anvin" <hpa@...or.com>,
Michael Ellerman <mpe@...erman.id.au>,
Mathias Krause <minipli@...glemail.com>,
Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
Arnd Bergmann <arnd@...db.de>, PaX Team <pageexec@...email.hu>,
Emese Revfy <re.emese@...il.com>, kernel-hardening@...ts.openwall.com,
linux-arch <linux-arch@...r.kernel.org>
Subject: [PATCH v3 4/8] init: create cmdline param to disable readonly
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.
Suggested-by: H. Peter Anvin <hpa@...or.com>
Signed-off-by: Kees Cook <keescook@...omium.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 742f69d18fc8..21cf76dbba90 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3409,6 +3409,10 @@ 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 9e64d7097f1a..fbafa271531c 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 e1dbf4a2c69e..90ff129c88a2 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;
--
1.9.1
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