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authorJosh Poimboeuf <jpoimboe@redhat.com>2017-05-23 10:37:30 -0500
committerIngo Molnar <mingo@kernel.org>2017-05-24 09:05:16 +0200
commit519fb5c3350d1b5225b27b1cac55144f79351718 (patch)
tree77801591c6ebd1d89b4ca941f3560b796e0dcd86 /arch
parentebd574994c63164d538a197172157318f58ac647 (diff)
x86/unwind: Add end-of-stack check for ftrace handlers
Dave Jones and Steven Rostedt reported unwinder warnings like the following: WARNING: kernel stack frame pointer at ffff8800bda0ff30 in sshd:1090 has bad value 000055b32abf1fa8 In both cases, the unwinder was attempting to unwind from an ftrace handler into entry code. The callchain was something like: syscall entry code C function ftrace handler save_stack_trace() The problem is that the unwinder's end-of-stack logic gets confused by the way ftrace lays out the stack frame (with fentry enabled). I was able to recreate this warning with: echo call_usermodehelper_exec_async:stacktrace > /sys/kernel/debug/tracing/set_ftrace_filter (exit login session) I considered fixing this by changing the ftrace code to rewrite the stack to make the unwinder happy. But that seemed too intrusive after I implemented it. Instead, just add another check to the unwinder's end-of-stack logic to detect this special case. Side note: We could probably get rid of these end-of-stack checks by encoding the frame pointer for syscall entry just like we do for interrupt entry. That would be simpler, but it would also be a lot more intrusive since it would slightly affect the performance of every syscall. Reported-by: Dave Jones <davej@codemonkey.org.uk> Reported-by: Steven Rostedt <rostedt@goodmis.org> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com> Acked-by: Thomas Gleixner <tglx@linutronix.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Petr Mladek <pmladek@suse.com> Cc: live-patching@vger.kernel.org Fixes: c32c47c68a0a ("x86/unwind: Warn on bad frame pointer") Link: http://lkml.kernel.org/r/671ba22fbc0156b8f7e0cfa5ab2a795e08bc37e1.1495553739.git.jpoimboe@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/kernel/unwind_frame.c49
1 files changed, 40 insertions, 9 deletions
diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index 82c6d7f1fd73..b9389d72b2f7 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -104,6 +104,11 @@ static inline unsigned long *last_frame(struct unwind_state *state)
return (unsigned long *)task_pt_regs(state->task) - 2;
}
+static bool is_last_frame(struct unwind_state *state)
+{
+ return state->bp == last_frame(state);
+}
+
#ifdef CONFIG_X86_32
#define GCC_REALIGN_WORDS 3
#else
@@ -115,16 +120,15 @@ static inline unsigned long *last_aligned_frame(struct unwind_state *state)
return last_frame(state) - GCC_REALIGN_WORDS;
}
-static bool is_last_task_frame(struct unwind_state *state)
+static bool is_last_aligned_frame(struct unwind_state *state)
{
unsigned long *last_bp = last_frame(state);
unsigned long *aligned_bp = last_aligned_frame(state);
/*
- * We have to check for the last task frame at two different locations
- * because gcc can occasionally decide to realign the stack pointer and
- * change the offset of the stack frame in the prologue of a function
- * called by head/entry code. Examples:
+ * GCC can occasionally decide to realign the stack pointer and change
+ * the offset of the stack frame in the prologue of a function called
+ * by head/entry code. Examples:
*
* <start_secondary>:
* push %edi
@@ -141,11 +145,38 @@ static bool is_last_task_frame(struct unwind_state *state)
* push %rbp
* mov %rsp,%rbp
*
- * Note that after aligning the stack, it pushes a duplicate copy of
- * the return address before pushing the frame pointer.
+ * After aligning the stack, it pushes a duplicate copy of the return
+ * address before pushing the frame pointer.
+ */
+ return (state->bp == aligned_bp && *(aligned_bp + 1) == *(last_bp + 1));
+}
+
+static bool is_last_ftrace_frame(struct unwind_state *state)
+{
+ unsigned long *last_bp = last_frame(state);
+ unsigned long *last_ftrace_bp = last_bp - 3;
+
+ /*
+ * When unwinding from an ftrace handler of a function called by entry
+ * code, the stack layout of the last frame is:
+ *
+ * bp
+ * parent ret addr
+ * bp
+ * function ret addr
+ * parent ret addr
+ * pt_regs
+ * -----------------
*/
- return (state->bp == last_bp ||
- (state->bp == aligned_bp && *(aligned_bp+1) == *(last_bp+1)));
+ return (state->bp == last_ftrace_bp &&
+ *state->bp == *(state->bp + 2) &&
+ *(state->bp + 1) == *(state->bp + 4));
+}
+
+static bool is_last_task_frame(struct unwind_state *state)
+{
+ return is_last_frame(state) || is_last_aligned_frame(state) ||
+ is_last_ftrace_frame(state);
}
/*