Re: [PATCH] mini-os: Avoid segfaults in tc{g,s}etattr

[Jason Andryuk <jandryuk@xxxxxxxxx>]

On Mon, Apr 27, 2020 at 3:54 AM Samuel Thibault
<samuel.thibault@xxxxxxxxxxxx> wrote:
>
> Jason Andryuk, le dim. 26 avril 2020 23:40:19 -0400, a ecrit:
> > Commit c96c22f1d94 "mini-os: minimal implementations of some termios
> > functions" introduced implementations of tcgetattr and tcsetattr.
> > However, they do not check if files[fildes].cons.dev is non-NULL before
> > dereferencing.  This is not a problem for FDs allocated through
> > alloc_fd, but the files array pre-allocates FDs 0-2 for stdio.  Those
> > entries have a NULL .dev, so tc{g,s}etattr on them segfault.
> >
> > ioemu-stubdom segfaults when term_init() calls tcgetattr on FD 0.
> >
> > Restore tcgetattr and tcsetattr behavior when .dev is NULL equivalent to
> > unsupported_function as it was before c96c22f1d94.
> >
> > Signed-off-by: Jason Andryuk <jandryuk@xxxxxxxxx>
>
> Reviewed-by: Samuel Thibault <samuel.thibault@xxxxxxxxxxxx>
>
> Thanks!

Thank you!

> > ---
> > I can't get ioemu-stubdom to start without this.  With this, the guest
> > just reboots immediately, but it does that with a non-stubdom
> > device_model_version="qemu-xen-traditional" .  The same guest disk image
> > (cirros 0.5.1) boots with a linux stubdom or non-stubdom Ubuntu
> > qemu-system-x86_64.

Ubuntu gcc-9 adds -fcf-protection by default.  Somehow that flag
caused rombios (I think) to restart.  Setting -fcf-protection=none
like below (probably just the EMBEDDED_EXTRA_CFLAGS part) lets rombios
start properly.  The hypervisor needs it as well via
EXTRA_CFLAGS_XEN_CORE=-fcf-protection=none and maybe also added to
xen/arch/x86/boot/build32.mk .

diff --git a/Config.mk b/Config.mk
index 0f303c79b2..efb3d42bc4 100644
--- 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
+EMBEDDED_EXTRA_CFLAGS += -fcf-protection=none

 XEN_EXTFILES_URL ?= http://xenbits.xen.org/xen-extfiles
 # All the files at that location were downloaded from elsewhere on
diff --git a/tools/firmware/Rules.mk b/tools/firmware/Rules.mk
index 26bbddccd4..0d33514d53 100644
--- a/tools/firmware/Rules.mk
+++ b/tools/firmware/Rules.mk
@@ -17,3 +17,4 @@ $(call cc-options-add,CFLAGS,CC,$(EMBEDDED_EXTRA_CFLAGS))

 # Extra CFLAGS suitable for an embedded type of environment.
 CFLAGS += -fno-builtin -msoft-float
+CFLAGS += -fcf-protection=none