linux-kernel - [PATCH v2 0/3] objtool: Support the stack swizzle

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Date:   Tue, 09 Feb 2021 10:16:00 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Miroslav Benes <mbenes@...e.cz>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Julien Thierry <jthierry@...hat.com>,
        Kees Cook <keescook@...omium.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org
Subject: [PATCH v2 0/3] objtool: Support the stack swizzle

Hi!

Implement objtool support for the x86_64 stack swizzle pattern.

This means we can use the minial stack swizzle:

  mov %rsp, (%[tos])
  mov %[tos], %rsp
  ...
  pop %rsp

from inline asm, with arbitrary stack setup. The ORC data for the Top-of-Stack
will use the SP_INDIRECT CFA base. In order for this to work, SP_INDIRECT needs
to first dereference and then add the offset to find the next frame.

Therefore we need to change SP_INDIRECT (which is currently unused) to mean:
(%rsp) + offset.

Changes since v1 include:

 - removed the !callee saved reg restriction by using the vals[] array
   over the regs[] array.

 - per the above, removed the patches creating the regs[] scratch space.

 - more comments.

 - rebased to tip/objtool/core