lwn.git/arch/x86/kernel/stacktrace.c, branch v4.16-rc4

Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2018-01-04T00:41:07+00:00

Pull x86 page table isolation fixes from Thomas Gleixner: "A couple of urgent fixes for PTI: - Fix a PTE mismatch between user and kernel visible mapping of the cpu entry area (differs vs. the GLB bit) and causes a TLB mismatch MCE on older AMD K8 machines - Fix the misplaced CR3 switch in the SYSCALL compat entry code which causes access to unmapped kernel memory resulting in double faults. - Fix the section mismatch of the cpu_tss_rw percpu storage caused by using a different mechanism for declaration and definition. - Two fixes for dumpstack which help to decode entry stack issues better - Enable PTI by default in Kconfig. We should have done that earlier, but it slipped through the cracks. - Exclude AMD from the PTI enforcement. Not necessarily a fix, but if AMD is so confident that they are not affected, then we should not burden users with the overhead" * 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/process: Define cpu_tss_rw in same section as declaration x86/pti: Switch to kernel CR3 at early in entry_SYSCALL_compat() x86/dumpstack: Print registers for first stack frame x86/dumpstack: Fix partial register dumps x86/pti: Make sure the user/kernel PTEs match x86/cpu, x86/pti: Do not enable PTI on AMD processors x86/pti: Enable PTI by default

x86/dumpstack: Fix partial register dumps

2018-01-03T15:14:46+00:00

The show_regs_safe() logic is wrong. When there's an iret stack frame, it prints the entire pt_regs -- most of which is random stack data -- instead of just the five registers at the end. show_regs_safe() is also poorly named: the on_stack() checks aren't for safety. Rename the function to show_regs_if_on_stack() and add a comment to explain why the checks are needed. These issues were introduced with the "partial register dump" feature of the following commit: b02fcf9ba121 ("x86/unwinder: Handle stack overflows more gracefully") That patch had gone through a few iterations of development, and the above issues were artifacts from a previous iteration of the patch where 'regs' pointed directly to the iret frame rather than to the (partially empty) pt_regs. Tested-by: Alexander Tsoy Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Toralf Förster Cc: stable@vger.kernel.org Fixes: b02fcf9ba121 ("x86/unwinder: Handle stack overflows more gracefully") Link: http://lkml.kernel.org/r/5b05b8b344f59db2d3d50dbdeba92d60f2304c54.1514736742.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

x86/stacktrace: Make zombie stack traces reliable

2017-12-19T08:01:05+00:00

Commit: 1959a60182f4 ("x86/dumpstack: Pin the target stack when dumping it") changed the behavior of stack traces for zombies. Before that commit, /proc//stack reported the last execution path of the zombie before it died: [] do_exit+0x6f7/0xa80 [] do_group_exit+0x39/0xa0 [] __wake_up_parent+0x0/0x30 [] system_call_fastpath+0x16/0x1b [<00007fd128f9c4f9>] 0x7fd128f9c4f9 [] 0xffffffffffffffff After the commit, it just reports an empty stack trace. The new behavior is actually probably more correct. If the stack refcount has gone down to zero, then the task has already gone through do_exit() and isn't going to run anymore. The stack could be freed at any time and is basically gone, so reporting an empty stack makes sense. However, save_stack_trace_tsk_reliable() treats such a missing stack condition as an error. That can cause livepatch transition stalls if there are any unreaped zombies. Instead, just treat it as a reliable, empty stack. Reported-and-tested-by: Miroslav Benes Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: live-patching@vger.kernel.org Fixes: af085d9084b4 ("stacktrace/x86: add function for detecting reliable stack traces") Link: http://lkml.kernel.org/r/e4b09e630e99d0c1080528f0821fc9d9dbaeea82.1513631620.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

x86/stacktrace: Avoid recording save_stack_trace() wrappers

2017-09-29T17:44:03+00:00

The save_stack_trace() and save_stack_trace_tsk() wrappers of __save_stack_trace() add themselves to the call stack, and thus appear in the recorded stacktraces. This is redundant and wasteful when we have limited space to record the useful part of the backtrace with e.g. page_owner functionality. Fix this by making sure __save_stack_trace() is noinline (which matches the current gcc decision) and bumping the skip in the wrappers (save_stack_trace_tsk() only when called for the current task). This is similar to what was done for arm in 3683f44c42e9 ("ARM: stacktrace: avoid listing stacktrace functions in stacktrace") and is pending for arm64. Also make sure that __save_stack_trace_reliable() doesn't get this problem in the future by marking it __always_inline (which matches current gcc decision), per Josh Poimboeuf. Signed-off-by: Vlastimil Babka Acked-by: Josh Poimboeuf Cc: Linus Torvalds Cc: Miroslav Benes Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/20170929092335.2744-1-vbabka@suse.cz Signed-off-by: Ingo Molnar

stacktrace/x86: add function for detecting reliable stack traces

2017-03-08T08:18:02+00:00

For live patching and possibly other use cases, a stack trace is only useful if it can be assured that it's completely reliable. Add a new save_stack_trace_tsk_reliable() function to achieve that. Note that if the target task isn't the current task, and the target task is allowed to run, then it could be writing the stack while the unwinder is reading it, resulting in possible corruption. So the caller of save_stack_trace_tsk_reliable() must ensure that the task is either 'current' or inactive. save_stack_trace_tsk_reliable() relies on the x86 unwinder's detection of pt_regs on the stack. If the pt_regs are not user-mode registers from a syscall, then they indicate an in-kernel interrupt or exception (e.g. preemption or a page fault), in which case the stack is considered unreliable due to the nature of frame pointers. It also relies on the x86 unwinder's detection of other issues, such as: - corrupted stack data - stack grows the wrong way - stack walk doesn't reach the bottom - user didn't provide a large enough entries array Such issues are reported by checking unwind_error() and !unwind_done(). Also add CONFIG_HAVE_RELIABLE_STACKTRACE so arch-independent code can determine at build time whether the function is implemented. Signed-off-by: Josh Poimboeuf Reviewed-by: Miroslav Benes Acked-by: Ingo Molnar # for the x86 changes Signed-off-by: Jiri Kosina

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

2017-03-02T07:42:36+00:00

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

2017-03-02T07:42:34+00:00

x86/stacktrace: Convert save_stack_trace_*() to use the new unwinder

2016-09-20T06:29:33+00:00

Convert save_stack_trace_*() to use the new unwinder. dump_trace() has been deprecated. Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Byungchul Park Cc: Denys Vlasenko Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Nilay Vaish Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/815494c627d89887db0ce56ceffd58ad16ee6c21.1474045023.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar

x86/dumpstack: Pin the target stack when dumping it

2016-09-16T07:18:53+00:00

Specifically, pin the stack in save_stack_trace_tsk() and show_trace_log_lvl(). This will prevent a crash if the target task dies before or while dumping its stack once we start freeing task stacks early. Signed-off-by: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Jann Horn Cc: Josh Poimboeuf Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/cf0082cde65d1941a996d026f2b2cdbfaca17bfa.1474003868.git.luto@kernel.org Signed-off-by: Ingo Molnar

x86/dumpstack: Add get_stack_info() interface

2016-09-15T06:13:15+00:00

valid_stack_ptr() is buggy: it assumes that all stacks are of size THREAD_SIZE, which is not true for exception stacks. So the walk_stack() callbacks will need to know the location of the beginning of the stack as well as the end. Another issue is that in general the various features of a stack (type, size, next stack pointer, description string) are scattered around in various places throughout the stack dump code. Encapsulate all that information in a single place with a new stack_info struct and a get_stack_info() interface. Signed-off-by: Josh Poimboeuf Cc: Andy Lutomirski Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Byungchul Park Cc: Denys Vlasenko Cc: Frederic Weisbecker Cc: H. Peter Anvin Cc: Kees Cook Cc: Linus Torvalds Cc: Nilay Vaish Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/8164dd0db96b7e6a279fa17ae5e6dc375eecb4a9.1473905218.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar