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Re: [GIT PULL] EFI fix

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On Mon, 16 May, at 01:05:45PM, Linus Torvalds wrote:
> 
> So that whole 8-vs-16 offset confusion depends on the frame pointer!
> If frame pointers were enabled, it will be 16. If they weren't, it
> will be 8. That patch that changes it from 8 to 16 will just move the
> bug around. Before, it was correct when frame pointers were disabled
> and buggy otherwise. Now, it's correct if frame pointers are enabled,
> and buggy otherwise.
 
Urgh, right.

We didn't always use frame pointers in efi_call(), they were
introduced in commit 779c433b8ea5c ("x86/asm/efi: Create a stack frame
in efi_call()") earlier this year to stop objtool complaining.

I admit I totally missed the part about pulling arguments off the
stack when I reviewed that patch.

> I may be missing something, but I think that commit is pure garbage.

You're correct.

> I think the right fix is to just get rid of that silly conditional
> frame pointer thing, and always use frame pointers in this stub
> function. And then we don't need that (odd) load to get the old stack
> pointer into %rax - we can just use the frame pointer.
> 
> Something like the attached completely untested patch.

Looks good to me, but I haven't tested it.

Now I'm wondering whether other users of FRAME_BEGIN/FRAME_END make
this same mistake. Coccinelle might be able to detect it perhaps.

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Thread

[GIT PULL] EFI fix Ingo Molnar <mingo@kernel.org> - 2016-05-16 16:50 +0200
  Re: [GIT PULL] EFI fix Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-16 22:10 +0200
    Re: [GIT PULL] EFI fix Alex Thorlton <athorlton@sgi.com> - 2016-05-16 22:30 +0200
      Re: [GIT PULL] EFI fix Alex Thorlton <athorlton@sgi.com> - 2016-05-17 00:50 +0200
    [tip:x86/urgent] x86/efi: Fix 7-parameter efi_call()s tip-bot for Linus Torvalds <tipbot@zytor.com> - 2016-05-17 08:40 +0200
    Re: [GIT PULL] EFI fix Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-17 11:10 +0200
      Re: [GIT PULL] EFI fix Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-17 11:50 +0200
        Re: [GIT PULL] EFI fix Ingo Molnar <mingo@kernel.org> - 2016-05-17 12:30 +0200
          [PATCH] x86/asm/entry: fix stack return address retrieval in thunk Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-17 16:50 +0200
            Re: [PATCH] x86/asm/entry: fix stack return address retrieval in thunk Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-17 18:40 +0200
              Re: [PATCH] x86/asm/entry: fix stack return address retrieval in  thunk Steven Rostedt <rostedt@goodmis.org> - 2016-05-17 19:00 +0200
                Re: [PATCH] x86/asm/entry: fix stack return address retrieval in thunk Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-17 19:30 +0200
                Re: [PATCH] x86/asm/entry: fix stack return address retrieval in  thunk Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-17 19:30 +0200
              [PATCH v2] x86/asm/entry: fix stack return address retrieval in thunk Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-17 20:10 +0200
                Re: [PATCH v2] x86/asm/entry: fix stack return address retrieval in thunk Linus Torvalds <torvalds@linux-foundation.org> - 2016-05-17 20:40 +0200
                [tip:x86/urgent] x86/entry/64: Fix stack return address retrieval  in thunk tip-bot for Josh Poimboeuf <tipbot@zytor.com> - 2016-05-19 11:20 +0200
    Re: [GIT PULL] EFI fix Matt Fleming <matt@codeblueprint.co.uk> - 2016-05-23 14:10 +0200
      Re: [GIT PULL] EFI fix Josh Poimboeuf <jpoimboe@redhat.com> - 2016-05-23 14:40 +0200
        Re: [GIT PULL] EFI fix Ingo Molnar <mingo@kernel.org> - 2016-05-24 11:10 +0200

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