objtool: Track DRAP separately from callee-saved registers
authorJosh Poimboeuf <jpoimboe@redhat.com>
Thu, 10 Aug 2017 21:37:26 +0000 (16:37 -0500)
committerIngo Molnar <mingo@kernel.org>
Fri, 11 Aug 2017 12:06:15 +0000 (14:06 +0200)
commitbf4d1a83758368c842c94cab9661a75ca98bc848
tree8e6787d0a5c44d6c997f849efde293dea00aeee6
parent12b25729a194198e3c4289adaddc4115b10b094e
objtool: Track DRAP separately from callee-saved registers

When GCC realigns a function's stack, it sometimes uses %r13 as the DRAP
register, like:

  push %r13
  lea 0x10(%rsp), %r13
  and $0xfffffffffffffff0, %rsp
  pushq -0x8(%r13)
  push %rbp
  mov %rsp, %rbp
  push %r13
  ...
  mov -0x8(%rbp),%r13
  leaveq
  lea -0x10(%r13), %rsp
  pop %r13
  retq

Since %r13 was pushed onto the stack twice, its two stack locations need
to be stored separately.  The first push of %r13 is its original value,
and the second push of %r13 is the caller's stack frame address.

Since %r13 is a callee-saved register, we need to track the stack
location of its original value separately from the DRAP register.

This fixes the following false positive warning:

  lib/ubsan.o: warning: objtool: val_to_string.constprop.7()+0x97: leave instruction with modified stack frame

Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
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>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: baa41469a7b9 ("objtool: Implement stack validation 2.0")
Link: http://lkml.kernel.org/r/3da23a6d4c5b3c1e21fc2ccc21a73941b97ff20a.1502401017.git.jpoimboe@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
tools/objtool/check.c
tools/objtool/check.h