Re: [PATCH 3/3] Add support for OpenBSD

["Christoph Egger" <Christoph.Egger@amd.com>]

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On Wednesday 18 October 2006 17:51, Keir Fraser wrote:
> On 17/10/06 15:44, "Christoph Egger" <Christoph.Egger@amd.com> wrote:
> > This is the third and last patch.
> >
> > This patch makes the xen kernel buildable on OpenBSD by adding support
> > for ProPolice. ProPolice has been added to standard GCC in version 4.1.x
> > under the name Stack Smashing Protection (SSP).
>
> Gcc 4.1.x works fine for me already (under Linux at least). We specifically
> disable stack protection in xen/arch/x86/Rules.mk.

The stack protection is not just to improve security. With a stack protection,
it is more likely that you find off-by-one bugs like this:

void foo(void)
{
        char array[8];
        int i;

        for (i = 0; i <= 8; i++) {
             array[i] = 0;
        }
        .....
}


The propolice patch also contained a snippet, which necessary to make
the Xen kernel build independ if SSP is disabled or not.

I extracted this snippet into a separate patch to fix this build error:

gcc -Wall -Werror -Wstrict-prototypes -O2 -fomit-frame-pointer  -o 
boot/mkelf32 boot/mkelf32.c
boot/mkelf32.c:93:1: "swap16" redefined
In file included from /usr/include/machine/endian.h:68,
                 from /usr/include/sys/types.h:45,
                 from /usr/include/stdio.h:45,
                 from boot/mkelf32.c:11:
/usr/include/sys/endian.h:156:1: this is the location of the previous 
definition
boot/mkelf32.c:94:1: "swap32" redefined
/usr/include/sys/endian.h:157:1: this is the location of the previous 
definition
boot/mkelf32.c:95:1: "swap64" redefined
/usr/include/sys/endian.h:158:1: this is the location of the previous 
definition
gmake[2]: *** [boot/mkelf32] Error 1

This mail has two patches attached:
openbsd_buildfix.diff  - the absolute necessary patch to make the kernel build 
on OpenBSD
openbsd_propolice.diff - it adds support for SSP



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diff -r 20522afb2615 xen/arch/x86/boot/mkelf32.c
--- a/xen/arch/x86/boot/mkelf32.c	Wed Oct 18 19:23:32 2006 +0100
+++ b/xen/arch/x86/boot/mkelf32.c	Wed Oct 18 09:03:19 2006 +0200
@@ -90,9 +90,15 @@ static Elf32_Shdr out_shdr[] = {
     }
 };
 
+#ifndef swap16
 #define swap16(_v) ((((u16)(_v)>>8)&0xff)|(((u16)(_v)&0xff)<<8))
+#endif
+#ifndef swap32
 #define swap32(_v) (((u32)swap16((u16)(_v))<<16)|(u32)swap16((u32)((_v)>>16)))
+#endif
+#ifndef swap64
 #define swap64(_v) (((u64)swap32((u32)(_v))<<32)|(u64)swap32((u32)((_v)>>32)))
+#endif
 
 static int big_endian;
 

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diff -r 20522afb2615 xen/arch/x86/setup.c
--- a/xen/arch/x86/setup.c	Wed Oct 18 19:23:32 2006 +0100
+++ b/xen/arch/x86/setup.c	Wed Oct 18 09:03:33 2006 +0200
@@ -16,6 +16,7 @@
 #include <xen/percpu.h>
 #include <xen/hypercall.h>
 #include <xen/keyhandler.h>
+#include <xen/guard.h>
 #include <public/version.h>
 #include <asm/bitops.h>
 #include <asm/smp.h>
@@ -668,6 +669,8 @@ void __init __start_xen(multiboot_info_t
                         cmdline) != 0)
         panic("Could not set up DOM0 guest OS\n");
 
+    init_guard();
+
     /* Scrub RAM that is still free and so may go to an unprivileged domain. */
     scrub_heap_pages();
 
diff -r 20522afb2615 xen/common/Makefile
--- a/xen/common/Makefile	Wed Oct 18 19:23:32 2006 +0100
+++ b/xen/common/Makefile	Wed Oct 18 09:03:33 2006 +0200
@@ -5,6 +5,7 @@ obj-y += elf.o
 obj-y += elf.o
 obj-y += event_channel.o
 obj-y += grant_table.o
+obj-y += guard.o
 obj-y += kernel.o
 obj-y += keyhandler.o
 obj-y += lib.o
diff -r 20522afb2615 xen/common/guard.c
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/common/guard.c	Wed Oct 18 09:03:33 2006 +0200
@@ -0,0 +1,34 @@
+
+#include <xen/lib.h>
+
+long __guard[8];
+
+void __stack_smash_handler(char [], int __attribute__((unused)));
+
+void
+__stack_smash_handler(char func[], int damaged)
+{
+        panic("smashed stack in %s", func);
+}
+
+
+void init_guard(void)
+{
+	volatile long newguard[8];
+	int i;
+
+	/* XXX newguard is intended to get filled with random values.
+	 * But there's nothing to use, so this is just something
+	 * out of my head :) */
+	newguard[0] = 103958;
+	newguard[1] = 3505;
+	newguard[2] = 75601;
+	newguard[3] = 35703;
+	newguard[4] = 94;
+	newguard[5] = 721;
+	newguard[6] = 3094;
+	newguard[7] = 217;
+
+	for (i = sizeof(__guard) / sizeof(__guard[0]) - 1; i; i--)
+		__guard[i] = newguard[i];
+}
diff -r 20522afb2615 xen/include/xen/guard.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/xen/include/xen/guard.h	Wed Oct 18 09:03:33 2006 +0200
@@ -0,0 +1,3 @@
+
+
+void init_guard(void);

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