user/sven/linux.git/kernel/debug/kdb, branch v4.14.7

kdb: Fix handling of kallsyms_symbol_next() return value

2017-12-14T08:52:58Z

commit c07d35338081d107e57cf37572d8cc931a8e32e2 upstream. kallsyms_symbol_next() returns a boolean (true on success). Currently kdb_read() tests the return value with an inequality that unconditionally evaluates to true. This is fixed in the obvious way and, since the conditional branch is supposed to be unreachable, we also add a WARN_ON(). Reported-by: Dan Carpenter Signed-off-by: Daniel Thompson Signed-off-by: Jason Wessel Signed-off-by: Greg Kroah-Hartman

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:34Z

We are going to split out of , which will have to be picked up from other headers and a couple of .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:34Z

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:29Z

sched/headers: Prepare for new header dependencies before moving code to

2017-03-02T07:42:27Z

We are going to split out of , which will have to be picked up from a couple of .c files. Create a trivial placeholder file that just maps to to make this patch obviously correct and bisectable. Include the new header in the files that are going to need it. Acked-by: Linus Torvalds Cc: Mike Galbraith Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

kdb: call vkdb_printf() from vprintk_default() only when wanted

2016-12-15T00:04:08Z

kdb_trap_printk allows to pass normal printk() messages to kdb via vkdb_printk(). For example, it is used to get backtrace using the classic show_stack(), see kdb_show_stack(). vkdb_printf() tries to avoid a potential infinite loop by disabling the trap. But this approach is racy, for example: CPU1 CPU2 vkdb_printf() // assume that kdb_trap_printk == 0 saved_trap_printk = kdb_trap_printk; kdb_trap_printk = 0; kdb_show_stack() kdb_trap_printk++; Problem1: Now, a nested printk() on CPU0 calls vkdb_printf() even when it should have been disabled. It will not cause a deadlock but... // using the outdated saved value: 0 kdb_trap_printk = saved_trap_printk; kdb_trap_printk--; Problem2: Now, kdb_trap_printk == -1 and will stay like this. It means that all messages will get passed to kdb from now on. This patch removes the racy saved_trap_printk handling. Instead, the recursion is prevented by a check for the locked CPU. The solution is still kind of racy. A non-related printk(), from another process, might get trapped by vkdb_printf(). And the wanted printk() might not get trapped because kdb_printf_cpu is assigned. But this problem existed even with the original code. A proper solution would be to get_cpu() before setting kdb_trap_printk and trap messages only from this CPU. I am not sure if it is worth the effort, though. In fact, the race is very theoretical. When kdb is running any of the commands that use kdb_trap_printk there is a single active CPU and the other CPUs should be in a holding pen inside kgdb_cpu_enter(). The only time this is violated is when there is a timeout waiting for the other CPUs to report to the holding pen. Finally, note that the situation is a bit schizophrenic. vkdb_printf() explicitly allows recursion but only from KDB code that calls kdb_printf() directly. On the other hand, the generic printk() recursion is not allowed because it might cause an infinite loop. This is why we could not hide the decision inside vkdb_printf() easily. Link: http://lkml.kernel.org/r/1480412276-16690-4-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek Cc: Daniel Thompson Cc: Jason Wessel Cc: Peter Zijlstra Cc: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kdb: properly synchronize vkdb_printf() calls with other CPUs

2016-12-15T00:04:08Z

kdb_printf_lock does not prevent other CPUs from entering the critical section because it is ignored when KDB_STATE_PRINTF_LOCK is set. The problematic situation might look like: CPU0 CPU1 vkdb_printf() if (!KDB_STATE(PRINTF_LOCK)) KDB_STATE_SET(PRINTF_LOCK); spin_lock_irqsave(&kdb_printf_lock, flags); vkdb_printf() if (!KDB_STATE(PRINTF_LOCK)) BANG: The PRINTF_LOCK state is set and CPU1 is entering the critical section without spinning on the lock. The problem is that the code tries to implement locking using two state variables that are not handled atomically. Well, we need a custom locking because we want to allow reentering the critical section on the very same CPU. Let's use solution from Petr Zijlstra that was proposed for a similar scenario, see https://lkml.kernel.org/r/20161018171513.734367391@infradead.org This patch uses the same trick with cmpxchg(). The only difference is that we want to handle only recursion from the same context and therefore we disable interrupts. In addition, KDB_STATE_PRINTF_LOCK is removed. In fact, we are not able to set it a non-racy way. Link: http://lkml.kernel.org/r/1480412276-16690-3-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek Reviewed-by: Daniel Thompson Cc: Jason Wessel Cc: Peter Zijlstra Cc: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

kdb: remove unused kdb_event handling

2016-12-15T00:04:08Z

kdb_event state variable is only set but never checked in the kernel code. http://www.spinics.net/lists/kdb/msg01733.html suggests that this variable affected WARN_CONSOLE_UNLOCKED() in the original implementation. But this check never went upstream. The semantic is unclear and racy. The value is updated after the kdb_printf_lock is acquired and after it is released. It should be symmetric at minimum. The value should be manipulated either inside or outside the locked area. Fortunately, it seems that the original function is gone and we could simply remove the state variable. Link: http://lkml.kernel.org/r/1480412276-16690-2-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek Suggested-by: Daniel Thompson Cc: Jason Wessel Cc: Peter Zijlstra Cc: Sergey Senozhatsky Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

printk/kdb: handle more message headers

2016-12-13T02:55:09Z

Commit 4bcc595ccd80 ("printk: reinstate KERN_CONT for printing continuation lines") allows to define more message headers for a single message. The motivation is that continuous lines might get mixed. Therefore it make sense to define the right log level for every piece of a cont line. This patch introduces printk_skip_headers() that will skip all headers and uses it in the kdb code instead of printk_skip_level(). This approach helps to fix other printk_skip_level() users independently. Link: http://lkml.kernel.org/r/1478695291-12169-3-git-send-email-pmladek@suse.com Signed-off-by: Petr Mladek Cc: Joe Perches Cc: Sergey Senozhatsky Cc: Steven Rostedt Cc: Jason Wessel Cc: Jaroslav Kysela Cc: Takashi Iwai Cc: Chris Mason Cc: Josef Bacik Cc: David Sterba Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

mm/init: Add 'rodata=off' boot cmdline parameter to disable read-only kernel mappings

2016-02-22T07:51:37Z

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 Signed-off-by: Kees Cook Cc: Andy Lutomirski Cc: Arnd Bergmann Cc: Borislav Petkov Cc: Brian Gerst Cc: David Brown Cc: Denys Vlasenko Cc: Emese Revfy Cc: Linus Torvalds Cc: Mathias Krause Cc: Michael Ellerman Cc: PaX Team Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kernel-hardening@lists.openwall.com Cc: linux-arch Link: http://lkml.kernel.org/r/1455748879-21872-3-git-send-email-keescook@chromium.org Signed-off-by: Ingo Molnar