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From: Jan Beulich <jbeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xenproject.org>,
	"Jason Andryuk" <jandryuk@gmail.com>,
	"Stefan Bader" <stefan.bader@canonical.com>,
	"Wei Liu" <wl@xen.org>, "Roger Pau Monné" <roger.pau@citrix.com>
Subject: Re: [PATCH] x86/build: Unilaterally disable -fcf-protection
Date: Wed, 13 May 2020 16:13:28 +0200	[thread overview]
Message-ID: <a56bb718-47e8-ab45-d706-84f59d3131d8@suse.com> (raw)
In-Reply-To: <20200513135552.24329-3-andrew.cooper3@citrix.com>

On 13.05.2020 15:55, Andrew Cooper wrote:
> Xen doesn't support CET-IBT yet.  At a minimum, logic is required to enable it
> for supervisor use, but the livepatch functionality needs to learn not to
> overwrite ENDBR64 instructions.
> 
> Furthermore, Ubuntu enables -fcf-protection by default, along with a buggy
> version of GCC-9 which objects to it in combination with
> -mindirect-branch=thunk-extern (Fixed in GCC 10, 9.4).
> 
> Various objects (Xen boot path, Rombios 32 stubs) require .text to be at the
> beginning of the object.  These paths explode when .note.gnu.properties gets
> put ahead of .text and we end up executing the notes data.
> 
> Disable -fcf-protection for all embedded objects.
> 
> Reported-by: Jason Andryuk <jandryuk@gmail.com>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

For the immediate purpose
Reviewed-by: Jan Beulich <jbeulich@suse.com>

I wonder however ...

> --- a/Config.mk
> +++ b/Config.mk
> @@ -205,6 +205,7 @@ APPEND_CFLAGS += $(foreach i, $(APPEND_INCLUDES), -I$(i))
>  
>  EMBEDDED_EXTRA_CFLAGS := -nopie -fno-stack-protector -fno-stack-protector-all
>  EMBEDDED_EXTRA_CFLAGS += -fno-exceptions -fno-asynchronous-unwind-tables
> +EMBEDDED_EXTRA_CFLAGS += -fcf-protection=none

... whether this isn't going to bite us once some of the consumers
of this variable want to enable some different mode.

Jan


  reply	other threads:[~2020-05-13 14:13 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-13 13:55 [PATCH] build: Fix build with Ubuntu Andrew Cooper
2020-05-13 13:55 ` [PATCH] x86/build: move -fno-asynchronous-unwind-tables into EMBEDDED_EXTRA_CFLAGS Andrew Cooper
2020-05-13 14:11   ` Jan Beulich
2020-05-13 14:18     ` Samuel Thibault
2020-05-13 13:55 ` [PATCH] x86/build: Unilaterally disable -fcf-protection Andrew Cooper
2020-05-13 14:13   ` Jan Beulich [this message]
2020-05-13 14:40     ` Andrew Cooper
2020-05-13 14:54   ` Jason Andryuk
  -- strict thread matches above, loose matches on Subject: below --
2020-05-12 19:11 Andrew Cooper
2020-05-13  2:35 ` Jason Andryuk
2020-05-13 11:01   ` Andrew Cooper
2020-05-13 12:15     ` Jason Andryuk
2020-05-13  9:15 ` Jan Beulich

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