x86/unwind: Ensure stack pointer is aligned

With frame pointers disabled, on some older versions of GCC (like
4.8.3), it's possible for the stack pointer to get aligned at a
half-word boundary:

  00000000000004d0 <fib_table_lookup>:
       4d0:       41 57                   push   %r15
       4d2:       41 56                   push   %r14
       4d4:       41 55                   push   %r13
       4d6:       41 54                   push   %r12
       4d8:       55                      push   %rbp
       4d9:       53                      push   %rbx
       4da:       48 83 ec 24             sub    $0x24,%rsp

In such a case, the unwinder ends up reading the entire stack at the
wrong alignment.  Then the last read goes past the end of the stack,
hitting the stack guard page:

  BUG: stack guard page was hit at ffffc900217c4000 (stack is ffffc900217c0000..ffffc900217c3fff)
  kernel stack overflow (page fault): 0000 [#1] SMP
  ...

Fix it by ensuring the stack pointer is properly aligned before
unwinding.

Reported-by: Jirka Hladky <[email protected]>
Signed-off-by: Josh Poimboeuf <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Brian Gerst <[email protected]>
Cc: Denys Vlasenko <[email protected]>
Cc: H. Peter Anvin <[email protected]>
Cc: Linus Torvalds <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Fixes: 7c7900f89770 ("x86/unwind: Add new unwind interface and implementations")
Link: http://lkml.kernel.org/r/cff33847cc9b02fa548625aa23268ac574460d8d.1492436590.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <[email protected]>

0 files changed, 0 insertions, 0 deletions