From: Kees Cook keescook@chromium.org
commit d2aa1acad22f1bdd0cfa67b3861800e392254454 upstream.
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@zytor.com Signed-off-by: Kees Cook keescook@chromium.org Cc: Andy Lutomirski luto@amacapital.net Cc: Arnd Bergmann arnd@arndb.de Cc: Borislav Petkov bp@alien8.de Cc: Brian Gerst brgerst@gmail.com Cc: David Brown david.brown@linaro.org Cc: Denys Vlasenko dvlasenk@redhat.com Cc: Emese Revfy re.emese@gmail.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Mathias Krause minipli@googlemail.com Cc: Michael Ellerman mpe@ellerman.id.au Cc: PaX Team pageexec@freemail.hu Cc: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: kernel-hardening@lists.openwall.com Cc: linux-arch linux-arch@vger.kernel.org Link: http://lkml.kernel.org/r/1455748879-21872-3-git-send-email-keescook@chromium... Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: David Brown david.brown@linaro.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 cd03a0f..51bbc77 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -3289,6 +3289,10 @@ 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 2a89545..14f36d1 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' @@ -925,6 +922,28 @@ 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; @@ -933,7 +952,7 @@ 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;