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Commit a8b7a923 authored by Josh Poimboeuf's avatar Josh Poimboeuf Committed by Ingo Molnar
Browse files

x86/unwind: Silence entry-related warnings 



A few people have reported unwinder warnings like the following:

  WARNING: kernel stack frame pointer at ffffc90000fe7ff0 in rsync:1157 has bad value           (null)
  unwind stack type:0 next_sp:          (null) mask:2 graph_idx:0
  ffffc90000fe7f98: ffffc90000fe7ff0 (0xffffc90000fe7ff0)
  ffffc90000fe7fa0: ffffffffb7000f56 (trace_hardirqs_off_thunk+0x1a/0x1c)
  ffffc90000fe7fa8: 0000000000000246 (0x246)
  ffffc90000fe7fb0: 0000000000000000 ...
  ffffc90000fe7fc0: 00007ffe3af639bc (0x7ffe3af639bc)
  ffffc90000fe7fc8: 0000000000000006 (0x6)
  ffffc90000fe7fd0: 00007f80af433fc5 (0x7f80af433fc5)
  ffffc90000fe7fd8: 00007ffe3af638e0 (0x7ffe3af638e0)
  ffffc90000fe7fe0: 00007ffe3af638e0 (0x7ffe3af638e0)
  ffffc90000fe7fe8: 00007ffe3af63970 (0x7ffe3af63970)
  ffffc90000fe7ff0: 0000000000000000 ...
  ffffc90000fe7ff8: ffffffffb7b74b9a (entry_SYSCALL_64_after_swapgs+0x17/0x4f)

This warning can happen when unwinding a code path where an interrupt
occurred in x86 entry code before it set up the first stack frame.
Silently ignore any warnings for this case.

Reported-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Reported-by: default avatarDave Jones <davej@codemonkey.org.uk>
Signed-off-by: default avatarJosh Poimboeuf <jpoimboe@redhat.com>
Acked-by: default avatarThomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Fixes: c32c47c6 ("x86/unwind: Warn on bad frame pointer")
Link: http://lkml.kernel.org/r/dbd6838826466a60dc23a52098185bc973ce2f1e.1492020577.git.jpoimboe@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 6bcdf9d5

arch/x86/include/asm/unwind.h

+1 −0
Original line number Diff line number Diff line
@@ -12,6 +12,7 @@ struct unwind_state { 
	struct task_struct *task;

	int graph_idx;

#ifdef CONFIG_FRAME_POINTER

	bool got_irq;

	unsigned long *bp, *orig_sp;

	struct pt_regs *regs;

	unsigned long ip;

arch/x86/kernel/unwind_frame.c

+27 −9
Original line number Diff line number Diff line 
#include <linux/sched.h>

#include <linux/sched/task.h>

#include <linux/sched/task_stack.h>

#include <linux/interrupt.h>

#include <asm/sections.h>

#include <asm/ptrace.h>

#include <asm/bitops.h>

#include <asm/stacktrace.h>
@@ -72,6 +74,21 @@ static size_t regs_size(struct pt_regs *regs) 
	return sizeof(*regs);

}



static bool in_entry_code(unsigned long ip)

{

	char *addr = (char *)ip;



	if (addr >= __entry_text_start && addr < __entry_text_end)

		return true;



#if defined(CONFIG_FUNCTION_GRAPH_TRACER) || defined(CONFIG_KASAN)

	if (addr >= __irqentry_text_start && addr < __irqentry_text_end)

		return true;

#endif



	return false;

}



#ifdef CONFIG_X86_32

#define GCC_REALIGN_WORDS 3

#else
@@ -144,6 +161,7 @@ static bool update_stack_state(struct unwind_state *state, 
	if (regs) {

		frame = (unsigned long *)regs;

		len = regs_size(regs);

		state->got_irq = true;

	} else {

		frame = next_bp;

		len = FRAME_HEADER_SIZE;
@@ -239,16 +257,8 @@ bool unwind_next_frame(struct unwind_state *state) 
		next_bp = (unsigned long *)READ_ONCE_TASK_STACK(state->task, *state->bp);



	/* Move to the next frame if it's safe: */

	if (!update_stack_state(state, next_bp)) {

		/*

		 * Don't warn on bad regs->bp.  An interrupt in entry code

		 * might cause a false positive warning.

		 */

		if (state->regs)

			goto the_end;



	if (!update_stack_state(state, next_bp))

		goto bad_address;

	}



	return true;
@@ -263,6 +273,13 @@ bool unwind_next_frame(struct unwind_state *state) 
	if (state->task != current)

		goto the_end;



	/*

	 * Don't warn if the unwinder got lost due to an interrupt in entry

	 * code before the stack was set up:

	 */

	if (state->got_irq && in_entry_code(state->ip))

		goto the_end;



	if (state->regs) {

		printk_deferred_once(KERN_WARNING

			"WARNING: kernel stack regs at %p in %s:%d has bad 'bp' value %p\n",
@@ -289,6 +306,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, 


	memset(state, 0, sizeof(*state));

	state->task = task;

	state->got_irq = (regs);



	/* Don't even attempt to start from user mode regs: */

	if (regs && user_mode(regs)) {