Commit-ID: d2aa1acad22f1bdd0cfa67b3861800e392254454 Gitweb: http://git.kernel.org/tip/d2aa1acad22f1bdd0cfa67b3861800e392254454 Author: Kees Cook <keesc...@chromium.org> AuthorDate: Wed, 17 Feb 2016 14:41:13 -0800 Committer: Ingo Molnar <mi...@kernel.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 <h...@zytor.com> Signed-off-by: Kees Cook <keesc...@chromium.org> Cc: Andy Lutomirski <l...@amacapital.net> Cc: Arnd Bergmann <a...@arndb.de> Cc: Borislav Petkov <b...@alien8.de> Cc: Brian Gerst <brge...@gmail.com> Cc: David Brown <david.br...@linaro.org> Cc: Denys Vlasenko <dvlas...@redhat.com> Cc: Emese Revfy <re.em...@gmail.com> Cc: Linus Torvalds <torva...@linux-foundation.org> Cc: Mathias Krause <mini...@googlemail.com> Cc: Michael Ellerman <m...@ellerman.id.au> Cc: PaX Team <pagee...@freemail.hu> Cc: Peter Zijlstra <pet...@infradead.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: kernel-harden...@lists.openwall.com Cc: linux-arch <linux-a...@vger.kernel.org> Link: http://lkml.kernel.org/r/1455748879-21872-3-git-send-email-keesc...@chromium.org Signed-off-by: Ingo Molnar <mi...@kernel.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;
