Re: [PATCH v5] efi: Fix stack protector issues

From: Daniel Kiper <dkiper@net-space.pl>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: Glenn Washburn <development@efficientek.com>,
	grub-devel@gnu.org,
	Vladimir 'phcoder' Serbinenko <phcoder@gmail.com>
Subject: Re: [PATCH v5] efi: Fix stack protector issues
Date: Wed, 8 May 2024 18:07:30 +0200	[thread overview]
Message-ID: <20240508160730.3b7ycmx2my53g3j7@tomti.i.net-space.pl> (raw)
In-Reply-To: <CAMj1kXHpr4FPFEU1rAHgkut4FUBYpPqpGab2-XAiqHEHdaqocQ@mail.gmail.com>

On Mon, Apr 29, 2024 at 03:03:50PM +0200, Ard Biesheuvel wrote:
> On Sat, 27 Apr 2024 at 15:08, Glenn Washburn
> <development@efficientek.com> wrote:
> >
> > From: Ard Biesheuvel <ardb@kernel.org>
> >
> > The 'ground truth' stack protector cookie value is kept in a global
> > variable, and loaded in every function prologue and epilogue to store
> > it into resp. compare it with the stack slot holding the cookie.
> >
> > If the comparison fails, the program aborts, and this might occur
> > spuriously when the global variable changes values between the entry and
> > exit of a function. This implies that assigning the global variable at
> > boot should not involve any instrumented function calls, unless special
> > care is taken to ensure that the live call stack is synchronized, which
> > is non-trivial.
> >
> > So avoid any function calls, including grub_memcpy(), which is
> > unnecessary given that the stack cookie is always a suitably aligned
> > variable of the native word size.
> >
> > While at it, leave the last byte 0x0 to avoid inadvertent unbounded
> > strings on the stack.
> >
> > Note that the use of __attribute__((optimize)) is described as
> > unsuitable for production use in the GCC documentation, so let's drop
> > this as well now that it is no longer needed.
> >
> > Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
> > Reviewed-by: Glenn Washburn <development@efficientek.com>

I think this RB does not make a lot of sens if we have your SOB below.
I will drop the RB.

> > Signed-off-by: Glenn Washburn <development@efficientek.com>
>
> Thanks for taking care of this.

Yeah, thanks a lot Glenn!

> I'd ack it but that would make the signoff chain look even weirder :-)

:-)

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel

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